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Comparison of properties of 5a-reductase isozymes.* Table 1

Table 1 Comparison of properties of 5a-reductase isozymes.* Table 1

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Benign prostatic hyperplasia (BPH) is the noncancerous proliferation of the prostate gland associated with benign prostatic obstruction and lower urinary tract symptoms (LUTS) such as frequency, hesitancy, urgency, etc. Its prevalence increases with age affecting around 70% by the age of 70 years. High activity of 5a-reductase enzyme in humans results in excessive dihydrotestosterone levels in peripheral tissues and hence suppression of androgen action by 5a-reductase inhibitors is a logical treatment for BPH as they inhibit the conversion of testosterone to dihydrotestosterone. Finasteride (13) was the first steroidal 5a- reductase inhibitor approved by U.S. Food and Drug Administration (USFDA). In human it decreases the prostatic DHT level by 70-90% and reduces the prostatic size. Dutasteride (27) another related analogue has been approved in 2002. Unlike Finasteride, Dutasteride is a competitive inhibitor of both 5a-reductase type I and type II isozymes, reduced DHT levels >90% following 1 year of oral administration. A number of classes of non-steroidal inhibitors of 5a-reductase have also been synthesized generally by removing one or more rings from the azasteroidal structure or by an early non-steroidal lead (ONO-3805) (261). In this review all categories of inhibitors of 5a-reductase have been covered. Keywords: 5a-Reductase inhibitors Androgens Azasteroids Testosterone BPH 5a-Dihydrotestosterone
Benign prostatic hyperplasia (BPH) is the noncancerous proliferation of the prostate gland associated with benign prostatic obstruction and lower urinary tract symptoms (LUTS) such as frequency, hesitancy, urgency, etc. Its prevalence increases with age affecting around 70% by the age of 70 years. High activity of 5a-reductase enzyme in humans results in excessive dihydrotestosterone levels in peripheral tissues and hence suppression of androgen action by 5a-reductase inhibitors is a logical treatment for BPH as they inhibit the conversion of testosterone to dihydrotestosterone. Finasteride (13) was the first steroidal 5a- reductase inhibitor approved by U.S. Food and Drug Administration (USFDA). In human it decreases the prostatic DHT level by 70-90% and reduces the prostatic size. Dutasteride (27) another related analogue has been approved in 2002. Unlike Finasteride, Dutasteride is a competitive inhibitor of both 5a-reductase type I and type II isozymes, reduced DHT levels >90% following 1 year of oral administration. A number of classes of non-steroidal inhibitors of 5a-reductase have also been synthesized generally by removing one or more rings from the azasteroidal structure or by an early non-steroidal lead (ONO-3805) (261). In this review all categories of inhibitors of 5a-reductase have been covered. Keywords: 5a-Reductase inhibitors Androgens Azasteroids Testosterone BPH 5a-Dihydrotestosterone
Fig. 1. Site of action of 5a-reductase inhibitors. ee aS ee Oe, ae The proposed chemical mechanism of T (1) reduction to DHT (2) by 5a-reductase catalysis involves the formation of a binary com- plex between the enzyme and NADPH, followed by the formation of a ternary complex with the substrate T. A delocalized carbocation is
Fig. 1. Site of action of 5a-reductase inhibitors. ee aS ee Oe, ae The proposed chemical mechanism of T (1) reduction to DHT (2) by 5a-reductase catalysis involves the formation of a binary com- plex between the enzyme and NADPH, followed by the formation of a ternary complex with the substrate T. A delocalized carbocation is
Fig. 2. 5a-Reduction of 3-keto-A‘ steroids.
Fig. 2. 5a-Reduction of 3-keto-A‘ steroids.
Although some of the 3-azasteroids were synthesized by Doorenbos and Wu [32] and Mazur [33] in the early 1960s but Anderson and Liao in 1968 reported for the first time that steroidal N-oxido-3-aza-1,3,5(10)-triene is a good inhibitor of enzyme 5a- reductase [34]. Haffner in 1994, reported the synthesis of some novel 3-pyridyl-N-oxide steroids (3 and 4) [35] which mimic the enolate or enol like transition state of the enzyme-substrate com- plex.
Although some of the 3-azasteroids were synthesized by Doorenbos and Wu [32] and Mazur [33] in the early 1960s but Anderson and Liao in 1968 reported for the first time that steroidal N-oxido-3-aza-1,3,5(10)-triene is a good inhibitor of enzyme 5a- reductase [34]. Haffner in 1994, reported the synthesis of some novel 3-pyridyl-N-oxide steroids (3 and 4) [35] which mimic the enolate or enol like transition state of the enzyme-substrate com- plex.
possessing these features act as competitive inhibitors of testos- terone 5a-reductase, therefore, all of them could be regarded as a substrate of the enzyme 4-en-3-one steroids [38]. 4-Androsten-3- one-17-carboxylic acid (11) was identified as a potent inhibitor of 5a-reductase. 4-Azasteroids is one of the extensively studied and clinically used classes of azasteroidal 5a-reductase inhibitors. Voigt et al. in 1970, screened a large number of steroids including 23 steroidal hormones for their ability to inhibit the conversion of T (1) into DHT (2) by a crude cell free enzyme system isolated from rat ventral prostate [37]. In 1973, series of effective 5a-reductase inhibitors were synthesized and evaluated. From the studies it was estab- lished that the key structural requirements for the 5a-reductase inhibitory activity were presence of 4-en-3-one function and 17B- side chain having one or more oxygen functionalities. Molecules
possessing these features act as competitive inhibitors of testos- terone 5a-reductase, therefore, all of them could be regarded as a substrate of the enzyme 4-en-3-one steroids [38]. 4-Androsten-3- one-17-carboxylic acid (11) was identified as a potent inhibitor of 5a-reductase. 4-Azasteroids is one of the extensively studied and clinically used classes of azasteroidal 5a-reductase inhibitors. Voigt et al. in 1970, screened a large number of steroids including 23 steroidal hormones for their ability to inhibit the conversion of T (1) into DHT (2) by a crude cell free enzyme system isolated from rat ventral prostate [37]. In 1973, series of effective 5a-reductase inhibitors were synthesized and evaluated. From the studies it was estab- lished that the key structural requirements for the 5a-reductase inhibitory activity were presence of 4-en-3-one function and 17B- side chain having one or more oxygen functionalities. Molecules
In search for a nonreducible inhibitor of 5a-reductase, Merck and Co. in 1980 reported series of 4-azasteroids where C-4 of 3- oxo-5a-steroids was replaced by nitrogen. The studies showed that there was not only an increase in the 5a-reductase inhibitory activity but also retention of the in vivo activity [39,40]. Therefore, azasteroids were designed to mimic the putative enzyme-bound enolate intermediate by incorporating sp?-hybridized center at C- 3 and C-4. Thus a lactam was introduced in the ring A of the steroids to mimic the enol transition state of the enzyme-NADPH-substrate (E.NADPH.S) complex. Substitution at C-17 has been found to enhance potency by binding to a lipophilic pocket on the enzyme. These competitive inhibitors strongly interact with the enzyme at the active site and on other hand unlike the substrate cannot be fur- ther reduced to 5a-metabolites thus have in vivo inhibitory activity [41]. The steroidal pharmacophore provides an anchor between the key A-ring lactam and the C-17 substituent while the former acts as a transition state mimic of intermediate enolate, the latter signifi- cantly enhances potency via binding at a pocket largely lipophilic in nature. The key 4-aza-3-oxo-5a-androstane pharmacophore and the basic structure activity relationship (SAR) is outlined below (Fig. 3) [42,43].
In search for a nonreducible inhibitor of 5a-reductase, Merck and Co. in 1980 reported series of 4-azasteroids where C-4 of 3- oxo-5a-steroids was replaced by nitrogen. The studies showed that there was not only an increase in the 5a-reductase inhibitory activity but also retention of the in vivo activity [39,40]. Therefore, azasteroids were designed to mimic the putative enzyme-bound enolate intermediate by incorporating sp?-hybridized center at C- 3 and C-4. Thus a lactam was introduced in the ring A of the steroids to mimic the enol transition state of the enzyme-NADPH-substrate (E.NADPH.S) complex. Substitution at C-17 has been found to enhance potency by binding to a lipophilic pocket on the enzyme. These competitive inhibitors strongly interact with the enzyme at the active site and on other hand unlike the substrate cannot be fur- ther reduced to 5a-metabolites thus have in vivo inhibitory activity [41]. The steroidal pharmacophore provides an anchor between the key A-ring lactam and the C-17 substituent while the former acts as a transition state mimic of intermediate enolate, the latter signifi- cantly enhances potency via binding at a pocket largely lipophilic in nature. The key 4-aza-3-oxo-5a-androstane pharmacophore and the basic structure activity relationship (SAR) is outlined below (Fig. 3) [42,43].
In vitro screening of compounds 20-27 against type I and type II human steroid 5a-reductase. Table 3 Table 2
In vitro screening of compounds 20-27 against type I and type II human steroid 5a-reductase. Table 3 Table 2
In vitro screening of compounds 28-33 against human and rat prostatic 5a- reductase.
In vitro screening of compounds 28-33 against human and rat prostatic 5a- reductase.
Weintraub et al. in 1985 reported 20-(hydroxymethyl)-4- methyl-4-aza-2-oxa-5a-pregnan-3-ones and their corresponding 3-thiones (16-19). These compounds were tested in vitro for inhibition of testosterone 5a-reductase and were found to be weak inhibitors with Kjs in the 10-’ range. It was argued that replacement of C-2 in the steroid nucleus by oxygen in the case of 4-aza-3-oxo-steroids would convert it to a urethane (17) from a lactam (16), respectively, thereby enhancing the polarity at C-3 carbonyl, and its affinity for the enzyme active site [55].
Weintraub et al. in 1985 reported 20-(hydroxymethyl)-4- methyl-4-aza-2-oxa-5a-pregnan-3-ones and their corresponding 3-thiones (16-19). These compounds were tested in vitro for inhibition of testosterone 5a-reductase and were found to be weak inhibitors with Kjs in the 10-’ range. It was argued that replacement of C-2 in the steroid nucleus by oxygen in the case of 4-aza-3-oxo-steroids would convert it to a urethane (17) from a lactam (16), respectively, thereby enhancing the polarity at C-3 carbonyl, and its affinity for the enzyme active site [55].
P= Phosphoadenosine diphosphoribose
P= Phosphoadenosine diphosphoribose
Dutasteride (GG745), 17B-N-{2,5-bis(trifluoromethyl)- phenyl)}-3-oxo-4-aza-5a-androst-1-ene-17-carboxamide (27) had emerged as the most potent dual inhibitor from this group (Table 2) [57]. It has been approved by U.S. FDA in 2002, for the symptomatic treatment of BPH [58,59]. Unlike Finasteride (13), Dutasteride (27) is a competitive inhibitor of both 5a-reductase type I and 5a-reductase type II isozymes, reduced dihydrotestos- terone levels >90% following one year oral administration [60]. It is also a time dependent inhibitor as Finasteride (13) and it forms a stable complex with a slow rate of dissociation constant and does not bind to the androgen receptor [61]. By reducing DHT level, it reduces the size of enlarged prostate, so improving the urinary flow rate. It is about 60 times more potent than Finasteride (13) and has been shown to decrease the risk of acute urinary retention and BPH related surgery [62-64]. This greater degree of suppression of serum DHT has been found to correlate with the intraprostatic DHT suppression. Dual inhibition of 5a-reductase is more beneficial than selective type II inhibition as dual inhibition does not allow the escape of DHT which can formed through type I mediated synthesis thus providing greater efficacy as DHT levels are suppressed to a great extent. Long-term studies have shown that Dutasteride (27) a dual inhibitor is well tolerated during daily use for up to 2 years. It had a tolerability profile comparable to that
Dutasteride (GG745), 17B-N-{2,5-bis(trifluoromethyl)- phenyl)}-3-oxo-4-aza-5a-androst-1-ene-17-carboxamide (27) had emerged as the most potent dual inhibitor from this group (Table 2) [57]. It has been approved by U.S. FDA in 2002, for the symptomatic treatment of BPH [58,59]. Unlike Finasteride (13), Dutasteride (27) is a competitive inhibitor of both 5a-reductase type I and 5a-reductase type II isozymes, reduced dihydrotestos- terone levels >90% following one year oral administration [60]. It is also a time dependent inhibitor as Finasteride (13) and it forms a stable complex with a slow rate of dissociation constant and does not bind to the androgen receptor [61]. By reducing DHT level, it reduces the size of enlarged prostate, so improving the urinary flow rate. It is about 60 times more potent than Finasteride (13) and has been shown to decrease the risk of acute urinary retention and BPH related surgery [62-64]. This greater degree of suppression of serum DHT has been found to correlate with the intraprostatic DHT suppression. Dual inhibition of 5a-reductase is more beneficial than selective type II inhibition as dual inhibition does not allow the escape of DHT which can formed through type I mediated synthesis thus providing greater efficacy as DHT levels are suppressed to a great extent. Long-term studies have shown that Dutasteride (27) a dual inhibitor is well tolerated during daily use for up to 2 years. It had a tolerability profile comparable to that
of placebo with the exception of a modestly elevated incidence of impotence and decreased libido compared with placebo. Also Dutasteride did not clinically significantly impact bone metabolism markers, bone mineral density or lipid levels [65]. In a programme aimed at searching for novel 5a-reductase inhibitors a series of C-17-acylurea-substituted 4-azasteroids (28-33) (Table 3) were synthesized by Di Salle et al. in early 1990s exploiting the tolerance of functionality at this position. Signifi- cantly greater potency was found with the derivative containing C-4 methyl group and a saturated A-ring [66].
of placebo with the exception of a modestly elevated incidence of impotence and decreased libido compared with placebo. Also Dutasteride did not clinically significantly impact bone metabolism markers, bone mineral density or lipid levels [65]. In a programme aimed at searching for novel 5a-reductase inhibitors a series of C-17-acylurea-substituted 4-azasteroids (28-33) (Table 3) were synthesized by Di Salle et al. in early 1990s exploiting the tolerance of functionality at this position. Signifi- cantly greater potency was found with the derivative containing C-4 methyl group and a saturated A-ring [66].
In vitro screening of compounds 44-49 against type I and type II human 5a- reductase.
In vitro screening of compounds 44-49 against type I and type II human 5a- reductase.
In vitro screening of compounds 50-54 against type I and type II human 5a. reductase.
In vitro screening of compounds 50-54 against type I and type II human 5a. reductase.
In vitro screening of compounds 38-43 against type I and type II human steroid 5a-reductase.
In vitro screening of compounds 38-43 against type I and type II human steroid 5a-reductase.
Various 78-substituted derivatives have also been prepared. Preliminary screening of the compounds as inhibitors of 5a- reductase from human scalp and prostate revealed that the presence of 78-methyl substitution in ring B, presence of choles- terol type side chain at C-17 and ketone functionalities at C-3 in 4-azasteroids resulted in potent selective inhibitor against 5a- reductase type I [70].
Various 78-substituted derivatives have also been prepared. Preliminary screening of the compounds as inhibitors of 5a- reductase from human scalp and prostate revealed that the presence of 78-methyl substitution in ring B, presence of choles- terol type side chain at C-17 and ketone functionalities at C-3 in 4-azasteroids resulted in potent selective inhibitor against 5a- reductase type I [70].
Similarly in series of 17 -[(N-alkyl/aryl) alkyl) arylamido] derivatives (Table 6) exhibited highly potent inhibitory activity for human 5a-reductase type I [69].
Similarly in series of 17 -[(N-alkyl/aryl) alkyl) arylamido] derivatives (Table 6) exhibited highly potent inhibitory activity for human 5a-reductase type I [69].
In vitro screening of compounds 63-66 against human steroid 5a-reductase. In order to have specific and dual inhibitors of 5a-reductase Labrie and associates synthesized several steroids having lactam in ring A and substitution at 178 position. Several of the compound: were found active (Tables 9 and 10) [75]. Table 10 Table 9
In vitro screening of compounds 63-66 against human steroid 5a-reductase. In order to have specific and dual inhibitors of 5a-reductase Labrie and associates synthesized several steroids having lactam in ring A and substitution at 178 position. Several of the compound: were found active (Tables 9 and 10) [75]. Table 10 Table 9
In vitro screening of compounds 70-72 against human steroid 5a-reductase. Table 11 In vitro screening of compounds 67-69 against human steroid 5a-reductase.
In vitro screening of compounds 70-72 against human steroid 5a-reductase. Table 11 In vitro screening of compounds 67-69 against human steroid 5a-reductase.
In vitro screening of compound 73 against human steroid 5a-reductase.
In vitro screening of compound 73 against human steroid 5a-reductase.
In vitro screening of compound 74 against rat and human steroid 5a-reductase.
In vitro screening of compound 74 against rat and human steroid 5a-reductase.
In vitro screening of compounds 80-85 against human steroid 5a-reductase.
In vitro screening of compounds 80-85 against human steroid 5a-reductase.
In vitro screening of compounds 86-89 against human steroid 5a-reductase.
In vitro screening of compounds 86-89 against human steroid 5a-reductase.
In vitro screening of compounds 75-79 against human steroid 5a-reductase.
In vitro screening of compounds 75-79 against human steroid 5a-reductase.
In 1996, Giudici et al. reported the synthesis of FCE 28260 (73) [(22R,S)-N-(1,1,1-trifluoro-2-phenylprop-2-yl)-3-oxo-4-aza- 5a-androst-1-ene-178-carboxamide] (Table 12) as a potent dual inhibitor of both 5a-reductase isozymes and it was found to cause 74% reduction in the DHT levels [77].
In 1996, Giudici et al. reported the synthesis of FCE 28260 (73) [(22R,S)-N-(1,1,1-trifluoro-2-phenylprop-2-yl)-3-oxo-4-aza- 5a-androst-1-ene-178-carboxamide] (Table 12) as a potent dual inhibitor of both 5a-reductase isozymes and it was found to cause 74% reduction in the DHT levels [77].
CIBA-GEIGY Ltd. reported the synthesis of CGP53153 (N-(2-cyano-2-propyl)-3-oxo-4-aza-5a-androst-1-ene-17B- carboxamide) (74) (Table 13), a novel inhibitor of 5a-reductase and structurally related to Finasteride (13) was found to be 10 times more potent than Finasteride in reducing prostate weight of rat [78].
CIBA-GEIGY Ltd. reported the synthesis of CGP53153 (N-(2-cyano-2-propyl)-3-oxo-4-aza-5a-androst-1-ene-17B- carboxamide) (74) (Table 13), a novel inhibitor of 5a-reductase and structurally related to Finasteride (13) was found to be 10 times more potent than Finasteride in reducing prostate weight of rat [78].
4 Results are the mean +SE of 3 separate assays. Incubations were performed in the presence of 3 or 1 4M [?H] testosterone, for type I or type Il isozyme, respectively. In vitro screening of compound 90 against human steroid 5a-reductase.* Table 17
4 Results are the mean +SE of 3 separate assays. Incubations were performed in the presence of 3 or 1 4M [?H] testosterone, for type I or type Il isozyme, respectively. In vitro screening of compound 90 against human steroid 5a-reductase.* Table 17
In vitro screening of compounds 94-101 against human steroid 5a-reductase. Table 18
In vitro screening of compounds 94-101 against human steroid 5a-reductase. Table 18
The addition of N+-methyl substituent in A-ring increases human androgen receptor affinity while addition of unsaturation to the A-ring (A!) increased human androgen receptor binding. The unsubstituted carbanilides in the A!-N4-methy] series showed some selectivity for type I 5a-reductase over type II enzyme. Whereas addition of aryl substitution at the 2-position increased type II 5a-reductase binding, thus providing dual inhibitors with excellent human androgen receptor binding. Compound (87) was found to be the most potent inhibitor from this series (Table 16) [80]. In 1998, Salle et al. reported synthesis of a novel compound PNU 157706 [N-(1,1,1,3,3,3-hexafluorophenylpropyl)-3-oxo-4-aza-5a- androst-1-ene-178-carboxamide] (90) as a potent dual type I and type II 5a-reductase inhibitor. PNU 157706 (90) was found to reduce prostate weight 16-fold than Finasteride (13) while the EDs values being 0.12 and 1.9 mg/kg/day, respectively (Table 17) [81].
The addition of N+-methyl substituent in A-ring increases human androgen receptor affinity while addition of unsaturation to the A-ring (A!) increased human androgen receptor binding. The unsubstituted carbanilides in the A!-N4-methy] series showed some selectivity for type I 5a-reductase over type II enzyme. Whereas addition of aryl substitution at the 2-position increased type II 5a-reductase binding, thus providing dual inhibitors with excellent human androgen receptor binding. Compound (87) was found to be the most potent inhibitor from this series (Table 16) [80]. In 1998, Salle et al. reported synthesis of a novel compound PNU 157706 [N-(1,1,1,3,3,3-hexafluorophenylpropyl)-3-oxo-4-aza-5a- androst-1-ene-178-carboxamide] (90) as a potent dual type I and type II 5a-reductase inhibitor. PNU 157706 (90) was found to reduce prostate weight 16-fold than Finasteride (13) while the EDs values being 0.12 and 1.9 mg/kg/day, respectively (Table 17) [81].
Fig. 5. SAR of 6-azasteroids.
Fig. 5. SAR of 6-azasteroids.
In vitro screening of compounds 102-114 against human steroid 5a-reductase.
In vitro screening of compounds 102-114 against human steroid 5a-reductase.
Menzenbach et al. reported the synthesis of several 17- methylene-4-azasteroids as inhibitors of 5a-reductase. Azaestra- none II (93) was found to be inhibitor of 5a-reductase with ICs59 = 34 x 10! (for prostate) and IC59 =25 x 10~!° (for seminal vesicle) [83].
Menzenbach et al. reported the synthesis of several 17- methylene-4-azasteroids as inhibitors of 5a-reductase. Azaestra- none II (93) was found to be inhibitor of 5a-reductase with ICs59 = 34 x 10! (for prostate) and IC59 =25 x 10~!° (for seminal vesicle) [83].
Methylation at N-6 (95) and substitution of C-4 with small lipophilic groups such as Cl (96), Br (97) and CH3 (98) increases type I 5a-reductase activity selectivity 4-fold while type I 5a-reductase activity was decreased by unsaturation (99), 1,2 cycloproponation (100) and C-2-methylation (101). Initially a set of N-6, C-1, C-2, C-4 substituted derivatives of 6- aza-androst-4-en-3-ones (94-101) were prepared to explore the structure activity relationship of A- and B-rings versus type I and type II 5a-reductase (Table 18).
Methylation at N-6 (95) and substitution of C-4 with small lipophilic groups such as Cl (96), Br (97) and CH3 (98) increases type I 5a-reductase activity selectivity 4-fold while type I 5a-reductase activity was decreased by unsaturation (99), 1,2 cycloproponation (100) and C-2-methylation (101). Initially a set of N-6, C-1, C-2, C-4 substituted derivatives of 6- aza-androst-4-en-3-ones (94-101) were prepared to explore the structure activity relationship of A- and B-rings versus type I and type II 5a-reductase (Table 18).
A variety of C-17 amide-substituted 6-aza-androst-4-en-3-ones were prepared and evaluated against human type I and type II steroid 5a-reductase in order to optimize potency versus both isozymes of 5a-reductase. Out of the study two series of potent and selective C-17 amides were discovered, 2,5-disubstituted anilides and (arylcycloalky1) amides (115-121) (Table 20). Evaluation of some optimal compounds from this series in a chronic castrated rat model of 5a-reductase inhibitor induced prostate involution, and pharmacokinetic measurements identified compounds (117, 118, 120 and 121) with good in vivo efficacy and half-life in the dog for)
A variety of C-17 amide-substituted 6-aza-androst-4-en-3-ones were prepared and evaluated against human type I and type II steroid 5a-reductase in order to optimize potency versus both isozymes of 5a-reductase. Out of the study two series of potent and selective C-17 amides were discovered, 2,5-disubstituted anilides and (arylcycloalky1) amides (115-121) (Table 20). Evaluation of some optimal compounds from this series in a chronic castrated rat model of 5a-reductase inhibitor induced prostate involution, and pharmacokinetic measurements identified compounds (117, 118, 120 and 121) with good in vivo efficacy and half-life in the dog for)
In vitro screening of compounds 115-121 against human steroid 5a-reductase.
In vitro screening of compounds 115-121 against human steroid 5a-reductase.
Bergmann et al. synthesised 7-substituted 6-4-6-azasteroid derivatives (123) as 5a-reductase inhibitors [87]. But activity data was not reported for these compounds.
Bergmann et al. synthesised 7-substituted 6-4-6-azasteroid derivatives (123) as 5a-reductase inhibitors [87]. But activity data was not reported for these compounds.
6-Azacholesten-3-ones (Table 21) were assayed against both type I and type II 5a-reductase by Haffner [88]. All three com- pounds were found to be potent dual inhibitors of 5a-reductase. Unlike the 4-azasteroids the cholesterol side chain imparts very little selectivity between type | and type II 5a-reductase. It was also found that C-7 methyl group might provide a potent 5a- reductase | selective compound. The a-C-7 methyl diastereomer (124) proved to be 7-fold more active 5a-reductase I inhibitor than B-diastereomer (125).
6-Azacholesten-3-ones (Table 21) were assayed against both type I and type II 5a-reductase by Haffner [88]. All three com- pounds were found to be potent dual inhibitors of 5a-reductase. Unlike the 4-azasteroids the cholesterol side chain imparts very little selectivity between type | and type II 5a-reductase. It was also found that C-7 methyl group might provide a potent 5a- reductase | selective compound. The a-C-7 methyl diastereomer (124) proved to be 7-fold more active 5a-reductase I inhibitor than B-diastereomer (125).
R; =H or CH3; Rp =CH3; R3 =hydrogen, Alk-Ry4, X-Alk, C).¢-X- Alk, XCO-Alk, Co-Ar, CO-NH-Ar, CO-NH-Het, etc., where Alk is Cy_12 straight or branched alkyl, Ar is phenyl, X is O, N or S, Het is piperidinyl, piperizinyl, pirrolidinyl, pyrrolyl, etc.
R; =H or CH3; Rp =CH3; R3 =hydrogen, Alk-Ry4, X-Alk, C).¢-X- Alk, XCO-Alk, Co-Ar, CO-NH-Ar, CO-NH-Het, etc., where Alk is Cy_12 straight or branched alkyl, Ar is phenyl, X is O, N or S, Het is piperidinyl, piperizinyl, pirrolidinyl, pyrrolyl, etc.
Rahier and Taton have reported synthesis of several novel 6- aza-B-homosteroids but they were not tested for 5a-reductase inhibitory activity [91]. Later in 2000 and 2001, Wenge et al. [92] and Xie et al. described the synthesis of 6-azasteroids as 16B-Aryloxy, -alkoxy and heteroaryloxy 6-azasteroids of the general formula as given below were synthesised by Aster et al. and the compounds were found to be potent inhibitors of 5a-reductase [90]. Compound (128) was found to be potent inhibitor of human 5a-reductase type I with ICsg in the range of 0.1-1000 nM.
Rahier and Taton have reported synthesis of several novel 6- aza-B-homosteroids but they were not tested for 5a-reductase inhibitory activity [91]. Later in 2000 and 2001, Wenge et al. [92] and Xie et al. described the synthesis of 6-azasteroids as 16B-Aryloxy, -alkoxy and heteroaryloxy 6-azasteroids of the general formula as given below were synthesised by Aster et al. and the compounds were found to be potent inhibitors of 5a-reductase [90]. Compound (128) was found to be potent inhibitor of human 5a-reductase type I with ICsg in the range of 0.1-1000 nM.
Fang and Sharp in 1996 synthesized several 6-azaandrostenones yf the general structure (127) as 5a-reductase inhibitors [89].
Fang and Sharp in 1996 synthesized several 6-azaandrostenones yf the general structure (127) as 5a-reductase inhibitors [89].
In vitro screening of compounds 124-126 against human steroid 5a-reductase. Table 22 Table 21 potent phosphatidylinositol phosphalipase C (PI-PLC) inhibitors [93]. Kasal et al. in 2005 reported an efficient synthesis of 6- aza-allopregnanolone as neurosteroid analogues but not evaluated them for 5a-reductase inhibitory activity [94]. 7. 7-Azasteroids
In vitro screening of compounds 124-126 against human steroid 5a-reductase. Table 22 Table 21 potent phosphatidylinositol phosphalipase C (PI-PLC) inhibitors [93]. Kasal et al. in 2005 reported an efficient synthesis of 6- aza-allopregnanolone as neurosteroid analogues but not evaluated them for 5a-reductase inhibitory activity [94]. 7. 7-Azasteroids
In vitro screening of compounds 129-135 against human steroid 5a-reductase type ll
In vitro screening of compounds 129-135 against human steroid 5a-reductase type ll
The inhibitory potency of these compounds depends on the presence of bridgehead N-10 atom conjugated with 4-en-3-one moiety in A-ring, unsaturation in C-ring and substituent at C- 17 position. 19-nor-10-aza steroids have low transitional barrier energy values and more flexible as compared to 6-aza or 4- azasteroids [102]. In vitro screening of compounds 129-135 against human steroid 5a-reductase type lin DU-145 cells. Table 23
The inhibitory potency of these compounds depends on the presence of bridgehead N-10 atom conjugated with 4-en-3-one moiety in A-ring, unsaturation in C-ring and substituent at C- 17 position. 19-nor-10-aza steroids have low transitional barrier energy values and more flexible as compared to 6-aza or 4- azasteroids [102]. In vitro screening of compounds 129-135 against human steroid 5a-reductase type lin DU-145 cells. Table 23
In vitro screening of compounds 149-152 against human steroid 5a-reductase. Table 24
In vitro screening of compounds 149-152 against human steroid 5a-reductase. Table 24
14. Diazasteroids Regan and Hayes, in their exemplary work, have synthe- sized several 17- and 17a-aza-D-homosteroids from several 17-ketosteroid oximes [115]. But 17a-azasteroids attracted more attention when chandonium diiodide was established as a potent neuromuscular blocker [116]. 17 and 17a-Azasteroids have been found to possess numerous biological activities like gamma amino butyric acid (GABA) receptor antagonistic [117-119], antifungal [120], antineoplastic, mutagenic [121,122] and anti-inflammatory activity [123]. The most interesting aspect concerning 17-D-homo- azasteroids is the possibility of “inverted action” or “backbinding” as proposed by MacDonald et al. [124]. Their proposition was based on the fact that the steroids have the potential to bind in two orientations in the active site of various metabolizing enzymes. Marcus and Talalay [125] first reported that 3(17) B-hydroxysteroid dehydrogenase converts both T (1) and dehydroepiandrosterone (141) to androst-4-ene-3,17-dione (140) (Fig. 6a). Other examples of enzyme inhibition by inverted steroids have also appeared. The oxiranes 143 and 144 were found to be active site-directed, irre- versible inhibitors of 3-oxo-A>-steroid isomerase (Fig. 6b) [126] and the bromoacetates 147 and 148 act as affinity labels for estra- diol 178-dehydrogenase (Fig. 6c) [127]. Research on 5a-reductase inhibitors has shown that steroids without side chains can bind to enzymes with the A-ring of the substance simulating the D-ring of the substrate, while the D-ring emulates the A-ring. This could lead to 17-D-homo-azasteroids exhibiting same mechanism of action as 4-azasteroids. However, up to now, research has been concentrated on 4-azasteroids as 5a-reductase inhibitors and 17a-azasteroids remained unexplored avenue as far as their 5a-reductase inhibitory activity is concerned. Some 17a-azasteroids (149-152) evaluated for 5a-reductase inhibitory activity are summarized in the Table 24 [124]. Eberbach and coworkers reported in 1996 a novel access to 4,13-diazasteroid derivatives but they were not evaluated for 5a- reductase activity [128]. In the same year Stuart et al. first reported 4,17-diazasteroids as potential inhibitors of 5a-reductase. The Finasteride 17-aza-isomer (153) proved to be potent inhibitor of 5a-reductase II although less active than Finasteride (13) and its congeners. 4-Methylation (154) lowered the inhibition of the 5a-reductase II enzyme. Removal of A1(2) unsaturation led to the formation of compound (155) that is dual inhibitor of 5a-reductase type I and type II and 4-methylation of 155 led to the increase in activity in 156. While compound with A‘) (157) showed only a moderate inhibition of 5a-reductase II activity (Table 25) [129].
14. Diazasteroids Regan and Hayes, in their exemplary work, have synthe- sized several 17- and 17a-aza-D-homosteroids from several 17-ketosteroid oximes [115]. But 17a-azasteroids attracted more attention when chandonium diiodide was established as a potent neuromuscular blocker [116]. 17 and 17a-Azasteroids have been found to possess numerous biological activities like gamma amino butyric acid (GABA) receptor antagonistic [117-119], antifungal [120], antineoplastic, mutagenic [121,122] and anti-inflammatory activity [123]. The most interesting aspect concerning 17-D-homo- azasteroids is the possibility of “inverted action” or “backbinding” as proposed by MacDonald et al. [124]. Their proposition was based on the fact that the steroids have the potential to bind in two orientations in the active site of various metabolizing enzymes. Marcus and Talalay [125] first reported that 3(17) B-hydroxysteroid dehydrogenase converts both T (1) and dehydroepiandrosterone (141) to androst-4-ene-3,17-dione (140) (Fig. 6a). Other examples of enzyme inhibition by inverted steroids have also appeared. The oxiranes 143 and 144 were found to be active site-directed, irre- versible inhibitors of 3-oxo-A>-steroid isomerase (Fig. 6b) [126] and the bromoacetates 147 and 148 act as affinity labels for estra- diol 178-dehydrogenase (Fig. 6c) [127]. Research on 5a-reductase inhibitors has shown that steroids without side chains can bind to enzymes with the A-ring of the substance simulating the D-ring of the substrate, while the D-ring emulates the A-ring. This could lead to 17-D-homo-azasteroids exhibiting same mechanism of action as 4-azasteroids. However, up to now, research has been concentrated on 4-azasteroids as 5a-reductase inhibitors and 17a-azasteroids remained unexplored avenue as far as their 5a-reductase inhibitory activity is concerned. Some 17a-azasteroids (149-152) evaluated for 5a-reductase inhibitory activity are summarized in the Table 24 [124]. Eberbach and coworkers reported in 1996 a novel access to 4,13-diazasteroid derivatives but they were not evaluated for 5a- reductase activity [128]. In the same year Stuart et al. first reported 4,17-diazasteroids as potential inhibitors of 5a-reductase. The Finasteride 17-aza-isomer (153) proved to be potent inhibitor of 5a-reductase II although less active than Finasteride (13) and its congeners. 4-Methylation (154) lowered the inhibition of the 5a-reductase II enzyme. Removal of A1(2) unsaturation led to the formation of compound (155) that is dual inhibitor of 5a-reductase type I and type II and 4-methylation of 155 led to the increase in activity in 156. While compound with A‘) (157) showed only a moderate inhibition of 5a-reductase II activity (Table 25) [129].
4 N,N-Diethyl-3-oxo-4-methyl-4-aza-5a-androstrane-17B-carboxamide (4-MA) was used as a standard reference. In vitro screening of compounds 153-157 against human steroid 5a-reductase. Table 25
4 N,N-Diethyl-3-oxo-4-methyl-4-aza-5a-androstrane-17B-carboxamide (4-MA) was used as a standard reference. In vitro screening of compounds 153-157 against human steroid 5a-reductase. Table 25
8,13-Diaza steroids were also synthesized by G6éndés et al. in 1998 but not evaluated for 5a-reductase inhibitory activity [130].
8,13-Diaza steroids were also synthesized by G6éndés et al. in 1998 but not evaluated for 5a-reductase inhibitory activity [130].
In vitro screening of compounds 158-166 against human steroid 5a-reductase. Table 26 18. Steroidal 3-carboxylic/phosphonic/phosphinic acids A number of 3-androstene-3-carboxylic acids (158-166) (Table 26) were designed to mimic the putative enzyme-bound enolate intermediate by incorporating sp?-hybridized centers at C-3 and C-4 and, most critically, an anionic carboxylic acid at C-3 as a charged replacement for the enolate oxyanion. Because of presumably favorable electrostatic interaction between the carboxylate and the positively charged oxidized cofactor, the acrylate preferentially binds in a ternary complex with enzyme and NADP*, which leads to the uncompetitive kinetic mechanism [135-137]. Activity is enhanced in analogues possessing an addi- tional unsaturation at C-5 (162-167) along with A?-unsaturation. At C-17, diisopropyl (158) and pivalyl (163) amides were optimal. Epristeride (SK&F 105657) (163) entered the clinical trials for treatment of BPH and is a potent inhibitor of 5a-reductase II while a weak inhibitor of 5a-reductase I.
In vitro screening of compounds 158-166 against human steroid 5a-reductase. Table 26 18. Steroidal 3-carboxylic/phosphonic/phosphinic acids A number of 3-androstene-3-carboxylic acids (158-166) (Table 26) were designed to mimic the putative enzyme-bound enolate intermediate by incorporating sp?-hybridized centers at C-3 and C-4 and, most critically, an anionic carboxylic acid at C-3 as a charged replacement for the enolate oxyanion. Because of presumably favorable electrostatic interaction between the carboxylate and the positively charged oxidized cofactor, the acrylate preferentially binds in a ternary complex with enzyme and NADP*, which leads to the uncompetitive kinetic mechanism [135-137]. Activity is enhanced in analogues possessing an addi- tional unsaturation at C-5 (162-167) along with A?-unsaturation. At C-17, diisopropyl (158) and pivalyl (163) amides were optimal. Epristeride (SK&F 105657) (163) entered the clinical trials for treatment of BPH and is a potent inhibitor of 5a-reductase II while a weak inhibitor of 5a-reductase I.
In vitro screening of compounds 167-171 against human steroid 5a-reductase. Table 27 Aseries of estratriene-3-carboxylic acids containing an aromatic A-ring had also been synthesized (167-171) (Table 27) with struc- tural variations in the C-2 and C-4 substituents, in the degrees of
In vitro screening of compounds 167-171 against human steroid 5a-reductase. Table 27 Aseries of estratriene-3-carboxylic acids containing an aromatic A-ring had also been synthesized (167-171) (Table 27) with struc- tural variations in the C-2 and C-4 substituents, in the degrees of
Nitro derivatives also showed interesting structure activity relationship patterns compared to carboxylic acids, compound (172) was found to be potent competitive inhibitor by binding to E-NADPH complex [139]. The sulphonic acid (173) [140], phospho- nic acid (174) and phosphinic acid (175) also proved to be the potent inhibitors of human 5a-reductase but not so of rat 5a- reductase [141]. The affinities of phosphonic acid are relatively less than phosphinic acid derivatives because the increased bulk at the 3-substituent, leading to a steric intolerance for binding to enzyme. Overall 3-phosphosteroids were weaker inhibitors than their corresponding steroidal-3-carboxy steroids. The function of unsaturation in the B- and D-rings, and in the C-17 carboxamide alkyl groups. Despite lacking C-19 methyl group these compounds were found to be potent inhibitors of 5a-reductase [138].
Nitro derivatives also showed interesting structure activity relationship patterns compared to carboxylic acids, compound (172) was found to be potent competitive inhibitor by binding to E-NADPH complex [139]. The sulphonic acid (173) [140], phospho- nic acid (174) and phosphinic acid (175) also proved to be the potent inhibitors of human 5a-reductase but not so of rat 5a- reductase [141]. The affinities of phosphonic acid are relatively less than phosphinic acid derivatives because the increased bulk at the 3-substituent, leading to a steric intolerance for binding to enzyme. Overall 3-phosphosteroids were weaker inhibitors than their corresponding steroidal-3-carboxy steroids. The function of unsaturation in the B- and D-rings, and in the C-17 carboxamide alkyl groups. Despite lacking C-19 methyl group these compounds were found to be potent inhibitors of 5a-reductase [138].
In vitro screening of compounds 180-183 against human 5a-reductase.
In vitro screening of compounds 180-183 against human 5a-reductase.
20. 4-Substituted steroids [145]. 4-Cyanoprogesterone (185) was also found to be a potent inhibitor of both rat and human 5a-reductase enzymes (ICso val- ues = 0.045 and 0.050 LM, respectively). The mechanism of action ot 4-cyano steroidal inhibitor was assumed to be the transition state inhibitor because on reduction by the enzyme compound would form a stable 5-3-enol that would remain tightly bound to the active site [146,147].
20. 4-Substituted steroids [145]. 4-Cyanoprogesterone (185) was also found to be a potent inhibitor of both rat and human 5a-reductase enzymes (ICso val- ues = 0.045 and 0.050 LM, respectively). The mechanism of action ot 4-cyano steroidal inhibitor was assumed to be the transition state inhibitor because on reduction by the enzyme compound would form a stable 5-3-enol that would remain tightly bound to the active site [146,147].
The primary evidence of a dramatic increase in the affinity of 5a- reductase and an inhibitor with a 5-juncture of A-/B-ring and sp2 hybridization at the C-3 and C-4 positions was obtained from the inhibition with a mechanism-based inhibitor (5,20R)-4-diazo-21- hydroxy-20-methyl-pregn-6-en-3-one (177) (RMI-18,341). Dia- zoketone (177) had been reported to be a potent time-dependent inhibitor with a K; of 35 nM (time-dependency is considered indica- tive of irreversibility) [142].
The primary evidence of a dramatic increase in the affinity of 5a- reductase and an inhibitor with a 5-juncture of A-/B-ring and sp2 hybridization at the C-3 and C-4 positions was obtained from the inhibition with a mechanism-based inhibitor (5,20R)-4-diazo-21- hydroxy-20-methyl-pregn-6-en-3-one (177) (RMI-18,341). Dia- zoketone (177) had been reported to be a potent time-dependent inhibitor with a K; of 35 nM (time-dependency is considered indica- tive of irreversibility) [142].
However, none of the compounds showed activity near to that of the reference drug Finasteride (13) (ICs5y9 values being 45 and 3 nM for typeI and type II, respectively, in the corresponding study) [148]. Transferring the oxime group from positions 20 to 21 caused an increased selectivity toward type II isozyme. Z-21- Hydroxyiminopregn-4-en-3-one (195) was found to be a potential inhibitor of the type II (IC597=1.95 wM against human type | and 0.30 wM against human type II).
However, none of the compounds showed activity near to that of the reference drug Finasteride (13) (ICs5y9 values being 45 and 3 nM for typeI and type II, respectively, in the corresponding study) [148]. Transferring the oxime group from positions 20 to 21 caused an increased selectivity toward type II isozyme. Z-21- Hydroxyiminopregn-4-en-3-one (195) was found to be a potential inhibitor of the type II (IC597=1.95 wM against human type | and 0.30 wM against human type II).
involving O and N heteroatoms at position 178 of androst-4-en- 3-one, respectively, as 5a-reductase inhibitors. The ICs59 values of compounds vary between 270 and 600 nM. The relative inhibitory effect of the unsubsituted N-phenyl compound 196 is 0.20. Con- cerning the effects of substituents at position 4 of the phenyl ring in 196, the introduction of an ethyl (197) or ethoxy (199) group resulted in a weak enhancement of 5a-reductase inhibition. Substitution with halogens (200 and 201) or methoxy (198) caused lowering of inhibition ability [149].
involving O and N heteroatoms at position 178 of androst-4-en- 3-one, respectively, as 5a-reductase inhibitors. The ICs59 values of compounds vary between 270 and 600 nM. The relative inhibitory effect of the unsubsituted N-phenyl compound 196 is 0.20. Con- cerning the effects of substituents at position 4 of the phenyl ring in 196, the introduction of an ethyl (197) or ethoxy (199) group resulted in a weak enhancement of 5a-reductase inhibition. Substitution with halogens (200 and 201) or methoxy (198) caused lowering of inhibition ability [149].
24. 6-Methylene steroidal derivatives Certain 19-nor analogues have also been synthesized in order to improve the inhibitory activity in 16-methylated derivatives. TSAA- 291 (16-ethyl-178-hydroxy-4-estren-3-one) (208) was found to be the first anti-androgen known to have dual action of competitive inhibition of 5a-reductase activity and androgen receptor complex formation. It showed a K; of 1400 nM to the purified nuclei from rat prostatic tissues [151].
24. 6-Methylene steroidal derivatives Certain 19-nor analogues have also been synthesized in order to improve the inhibitory activity in 16-methylated derivatives. TSAA- 291 (16-ethyl-178-hydroxy-4-estren-3-one) (208) was found to be the first anti-androgen known to have dual action of competitive inhibition of 5a-reductase activity and androgen receptor complex formation. It showed a K; of 1400 nM to the purified nuclei from rat prostatic tissues [151].
As a consequence of the important observation that pro- gesterone and deoxycortisone inhibits the synthesis of dihy- drotestosterone by competing with 4-en-3-one function of the testosterone for the 5a-reductase enzyme it led Voigt and cowork- ers to synthesize number of progesterone derivatives [37,38]. The satisfactory result of 4-cyano-progesterone (185) [146], which
As a consequence of the important observation that pro- gesterone and deoxycortisone inhibits the synthesis of dihy- drotestosterone by competing with 4-en-3-one function of the testosterone for the 5a-reductase enzyme it led Voigt and cowork- ers to synthesize number of progesterone derivatives [37,38]. The satisfactory result of 4-cyano-progesterone (185) [146], which
(4R)-5,10-Seco-estra-4,5-diene-3,10,17-trione (211) and (4R)- 5,10-seco-19-nor-pregna-4,5-diene-3,10,20-trione (212) were first found to be non-competitive and possibly irreversible inhibitors of epididymal 5a-reductase. Radiographic crystallog- raphy studies of both compounds showed that the conjugated allenic 3-oxo-5,10-secosteriod (211) has a conformation similar to that of the normal tetracyclic steroid dione. Both compounds were non-competitive inhibitors of 5a-reductase and have an affinity label for the enzyme with Kk; of 5470 and 980nM, respectively [154,155]. possessed marked inhibitory activity for 5a-reductase enzyme, stimulated great deal of interest to synthesize various 4- and 6-halo-progesterone analogs (213-217). These compounds were found to be potent antiandrogenic in nature when tested against gonadectomized hamster seminal vesicles and were also found to be inhibitors of 5a-reductase [156-158].
(4R)-5,10-Seco-estra-4,5-diene-3,10,17-trione (211) and (4R)- 5,10-seco-19-nor-pregna-4,5-diene-3,10,20-trione (212) were first found to be non-competitive and possibly irreversible inhibitors of epididymal 5a-reductase. Radiographic crystallog- raphy studies of both compounds showed that the conjugated allenic 3-oxo-5,10-secosteriod (211) has a conformation similar to that of the normal tetracyclic steroid dione. Both compounds were non-competitive inhibitors of 5a-reductase and have an affinity label for the enzyme with Kk; of 5470 and 980nM, respectively [154,155]. possessed marked inhibitory activity for 5a-reductase enzyme, stimulated great deal of interest to synthesize various 4- and 6-halo-progesterone analogs (213-217). These compounds were found to be potent antiandrogenic in nature when tested against gonadectomized hamster seminal vesicles and were also found to be inhibitors of 5a-reductase [156-158].
Several new pregnane derivatives were also synthesized and evaluated by the conversion of [3H] T to [3H] DHT in Penicillium crustosum broths and the conversion of [1,2-!4C] sodium acetate into lipids. Compounds 228 and 229 were found out to be potent 5a-reductase inhibitors as they inhibit conversion of T to DHT and also decreased the incorporation of radiolabeled sodium acetate into lipids of the flank organs [162].
Several new pregnane derivatives were also synthesized and evaluated by the conversion of [3H] T to [3H] DHT in Penicillium crustosum broths and the conversion of [1,2-!4C] sodium acetate into lipids. Compounds 228 and 229 were found out to be potent 5a-reductase inhibitors as they inhibit conversion of T to DHT and also decreased the incorporation of radiolabeled sodium acetate into lipids of the flank organs [162].
The in vitro inhibitory activity of some novel progesterone derivatives was also determined and they were evaluated as 5a-reductase inhibitors as well as antagonists for the androgen Cabeza et al. also reported the 5a-reductase inhibitory activ- ity and the antiandrogenic effect of novel 16-bromo substituted trienedione, 168 methyl substituted dienedione and the triene- dione (230-232). Compounds 230 and 231 were found to Exhibit 5a-reductase inhibitory activity higher than the commercially available Finasteride (13) [163].
The in vitro inhibitory activity of some novel progesterone derivatives was also determined and they were evaluated as 5a-reductase inhibitors as well as antagonists for the androgen Cabeza et al. also reported the 5a-reductase inhibitory activ- ity and the antiandrogenic effect of novel 16-bromo substituted trienedione, 168 methyl substituted dienedione and the triene- dione (230-232). Compounds 230 and 231 were found to Exhibit 5a-reductase inhibitory activity higher than the commercially available Finasteride (13) [163].
In compound 237 which is an epoxy compound the nucleophilic enzyme attacked the electrophilic center at C-6 and in this process inhibits the enzyme. Several 3-substituted 4-pregnene-6,20-dione derivatives (238-246) have been synthesized and were evaluated for antiandrogenic as well as 5a-reductase inhibitory activity. The synthesized steroids have an a,B-unsaturated carbonyl moiety in common. It was found that accessible electrophilic B-carbon of an a,8-unsaturated carbonyl moiety reacted very readily with a variety of nucleophiles to form Michael adducts. The first step involved the formation of an enzyme-steroid activated complex and in a subsequent step the nucleophilic portion of the enzyme (amino group) attacked the conjugated double bond of the steroid in a Michael type addition reaction to form an irreversible adducts [166].
In compound 237 which is an epoxy compound the nucleophilic enzyme attacked the electrophilic center at C-6 and in this process inhibits the enzyme. Several 3-substituted 4-pregnene-6,20-dione derivatives (238-246) have been synthesized and were evaluated for antiandrogenic as well as 5a-reductase inhibitory activity. The synthesized steroids have an a,B-unsaturated carbonyl moiety in common. It was found that accessible electrophilic B-carbon of an a,8-unsaturated carbonyl moiety reacted very readily with a variety of nucleophiles to form Michael adducts. The first step involved the formation of an enzyme-steroid activated complex and in a subsequent step the nucleophilic portion of the enzyme (amino group) attacked the conjugated double bond of the steroid in a Michael type addition reaction to form an irreversible adducts [166].
receptor. The appropriate homologues extended by a methylene group at C-6 (233-236) showed better activity due to the pres- ence of exocyclic double bond that can react faster with the enzyme in a Michael type addition reaction than the corresponding endo- cyclic diene. Compounds 233 and 234 showed ICso values of 19 and 100 nM, respectively [164,165].
receptor. The appropriate homologues extended by a methylene group at C-6 (233-236) showed better activity due to the pres- ence of exocyclic double bond that can react faster with the enzyme in a Michael type addition reaction than the corresponding endo- cyclic diene. Compounds 233 and 234 showed ICso values of 19 and 100 nM, respectively [164,165].
In vitro screening of compounds 262-265 against human 5a-reductase. Table 29 enriched by the presence of halogens in these steroidal derivatives leading to the increase in the inhibition of 5a-reductase enzyme as determined by the ICs59 values. Compound 252 was found to be most potent with an ICso value of 1.8nM while compounds 251 and 253 showed values 14 and 10 nM, respectively, in comparison to Finasteride (13) having value 8.5nM. Compound 254 was not
In vitro screening of compounds 262-265 against human 5a-reductase. Table 29 enriched by the presence of halogens in these steroidal derivatives leading to the increase in the inhibition of 5a-reductase enzyme as determined by the ICs59 values. Compound 252 was found to be most potent with an ICso value of 1.8nM while compounds 251 and 253 showed values 14 and 10 nM, respectively, in comparison to Finasteride (13) having value 8.5nM. Compound 254 was not
Working on similar lines some more novel 4,16-pregnadiene- 6,20-dione derivatives were synthesized and evaluated as 5a- reductase inhibitors. In this work, it has been demonstrated that compounds containing chlorine (251), bromine (252), iodine (253) atoms, and (254); without any substituent in the ester moiety) at C- 3 produce a significant decrease of the prostate weight in castrated animals treated with testosterone (1). Therefore, it was proposed that the ester moiety at C-3 is functioning as a pharmacophore, Bratoeff et al. synthesized two novel steroidal carbamates (249-250) which are the esters of carbamic acid with substituents at the amino and esters ends (NHRCOOR!) and proposed them as novel class of inhibitors for human and hamster steroid 5a- reductase. These compounds have a longer half-life and are hydrolyzed slowly in the liver due to which they have a better phar- macological activity when compared to the conventional esters. Compound 249 has got a similar IC59 value (10 nM) as that of Finas- teride (8.5 nM) (13) while compound 250 has a higher ICs59 value of about 50 nM apparently due to the presence of large bromine atom [170].
Working on similar lines some more novel 4,16-pregnadiene- 6,20-dione derivatives were synthesized and evaluated as 5a- reductase inhibitors. In this work, it has been demonstrated that compounds containing chlorine (251), bromine (252), iodine (253) atoms, and (254); without any substituent in the ester moiety) at C- 3 produce a significant decrease of the prostate weight in castrated animals treated with testosterone (1). Therefore, it was proposed that the ester moiety at C-3 is functioning as a pharmacophore, Bratoeff et al. synthesized two novel steroidal carbamates (249-250) which are the esters of carbamic acid with substituents at the amino and esters ends (NHRCOOR!) and proposed them as novel class of inhibitors for human and hamster steroid 5a- reductase. These compounds have a longer half-life and are hydrolyzed slowly in the liver due to which they have a better phar- macological activity when compared to the conventional esters. Compound 249 has got a similar IC59 value (10 nM) as that of Finas- teride (8.5 nM) (13) while compound 250 has a higher ICs59 value of about 50 nM apparently due to the presence of large bromine atom [170].
Several new progesterone derivatives were also synthesized by the same group having dienone moiety as reported earlier. Some of them (247-248) were found to have high 5a-reductase inhibitory activity like 248 showing an ICs9 value of 0.5nM as compared to Finasteride (13) showing an ICs9 value of 8.5 nM in the same study [168,169].
Several new progesterone derivatives were also synthesized by the same group having dienone moiety as reported earlier. Some of them (247-248) were found to have high 5a-reductase inhibitory activity like 248 showing an ICs9 value of 0.5nM as compared to Finasteride (13) showing an ICs9 value of 8.5 nM in the same study [168,169].
Recently, Cabeza et al. synthesized several C-6 substituted and unsubstituted pregnane derivatives as potential 5a-reductase inhibitors. It has been found that steroids that lack a chlorine atom in C-6 (255-257) exhibited a higher capacity for inhibition of the activity of 5a-reductase (ICs59 in the range of 25-63 nM) than the compounds (258-260) having this atom (ICsg in the range of 920-990 nM in comparison to Finasteride (13) having an ICs9 8.5nM). The presence of bromine atom in C-6 of compound 261 however doesn’t affect the inhibitory activity of enzyme (ICs being 33nM). Also, the presence of an ester moiety in C-17 a on the steroidal skeleton tends to increase the inhibition of the activity of the enzyme [172]. that active when compared to halogenated compounds thus further demonstrating the need of a halogen atom in the ester side chain [171].
Recently, Cabeza et al. synthesized several C-6 substituted and unsubstituted pregnane derivatives as potential 5a-reductase inhibitors. It has been found that steroids that lack a chlorine atom in C-6 (255-257) exhibited a higher capacity for inhibition of the activity of 5a-reductase (ICs59 in the range of 25-63 nM) than the compounds (258-260) having this atom (ICsg in the range of 920-990 nM in comparison to Finasteride (13) having an ICs9 8.5nM). The presence of bromine atom in C-6 of compound 261 however doesn’t affect the inhibitory activity of enzyme (ICs being 33nM). Also, the presence of an ester moiety in C-17 a on the steroidal skeleton tends to increase the inhibition of the activity of the enzyme [172]. that active when compared to halogenated compounds thus further demonstrating the need of a halogen atom in the ester side chain [171].
A number of classes of non-steroidal inhibitors of 5a-reductase have now been identified. It was anticipated that the use of non- steroidal template can decrease the potential interaction with other enzyme or receptor of the steroidal endocrine system and can limit the complexity of target compound synthesis [173]. They have in fact emerged either from the design of compounds mimic of azas- teroidal inhibitors, generally by the formal removing of one or more rings from the azasteroidal structure or by early non-steroidal lead (ONO-3805) (261) which was prepared as leukotriene synthesis inhibitor [174] or by high throughput screening. These com- pounds are generally thought to act all as competitive inhibitors vs. testosterone with exception of the epristeride analogues which are uncompetitive inhibitors. Non-steroidal inhibitors include benzo[f]quinolinones, pyridones and quinolinones which were mimics of 4-azasteroid inhibitors. Benzo[c]quinolinones were syn- thesized as mimics of 6-azasteroids while benzo[c]quinolizinones were designed as mimics of 10-azasteroids. The most potent and selective inhibitors of human type I 5a-reductase are found among these classes of compounds. Almost all the other non-steroidal inhibitors can be grouped as carboxylic acid (generally butanoic acid) derivatives which are thought to act as non-competitive inhibitors versus testosterone in analogy to ONO 3805 (261). 28. Mimics of 4-azasteroids: benzo[f]quinolinones
A number of classes of non-steroidal inhibitors of 5a-reductase have now been identified. It was anticipated that the use of non- steroidal template can decrease the potential interaction with other enzyme or receptor of the steroidal endocrine system and can limit the complexity of target compound synthesis [173]. They have in fact emerged either from the design of compounds mimic of azas- teroidal inhibitors, generally by the formal removing of one or more rings from the azasteroidal structure or by early non-steroidal lead (ONO-3805) (261) which was prepared as leukotriene synthesis inhibitor [174] or by high throughput screening. These com- pounds are generally thought to act all as competitive inhibitors vs. testosterone with exception of the epristeride analogues which are uncompetitive inhibitors. Non-steroidal inhibitors include benzo[f]quinolinones, pyridones and quinolinones which were mimics of 4-azasteroid inhibitors. Benzo[c]quinolinones were syn- thesized as mimics of 6-azasteroids while benzo[c]quinolizinones were designed as mimics of 10-azasteroids. The most potent and selective inhibitors of human type I 5a-reductase are found among these classes of compounds. Almost all the other non-steroidal inhibitors can be grouped as carboxylic acid (generally butanoic acid) derivatives which are thought to act as non-competitive inhibitors versus testosterone in analogy to ONO 3805 (261). 28. Mimics of 4-azasteroids: benzo[f]quinolinones
27. Non-steroidal 5a-reductase inhibitors general octahydro derivatives are more potent inhibitors than the corresponding 4a-10a unsaturated compounds (Tables 29 and 30) and in both series the potency toward type I 5a-reductase increases if an halogen atom is present at position 8 (in particular a Cl atom) and a methyl group at position 4; in fact the most potent inhibitor of the series is LY191704 (268) with IC5,7=8nM (Table 30). This molecule has progressed into human clinical trials.
27. Non-steroidal 5a-reductase inhibitors general octahydro derivatives are more potent inhibitors than the corresponding 4a-10a unsaturated compounds (Tables 29 and 30) and in both series the potency toward type I 5a-reductase increases if an halogen atom is present at position 8 (in particular a Cl atom) and a methyl group at position 4; in fact the most potent inhibitor of the series is LY191704 (268) with IC5,7=8nM (Table 30). This molecule has progressed into human clinical trials.
29. Pyridones, quinolinones and piperidines than the corresponding lactams. The aryl acid 277 showed good dual isozyme inhibitory properties with significantly enhanced type II activity. Bicyclic lactams, in general, were found to be less active against type I 5a-reductase than the tricycles. For example, compounds (278-279), lacking the B and D steroidal rings, were poor type I 5a-reductase inhibitors, with the highest potency associated to the presence of the Cl atom on the aromatic ring of 279 [178]. A styryl (or azo) substituent dramatically enhances type II activity (and indeed type I activity with the bicycles) (280-281) and provided dual inhibitors of type I and type II.
29. Pyridones, quinolinones and piperidines than the corresponding lactams. The aryl acid 277 showed good dual isozyme inhibitory properties with significantly enhanced type II activity. Bicyclic lactams, in general, were found to be less active against type I 5a-reductase than the tricycles. For example, compounds (278-279), lacking the B and D steroidal rings, were poor type I 5a-reductase inhibitors, with the highest potency associated to the presence of the Cl atom on the aromatic ring of 279 [178]. A styryl (or azo) substituent dramatically enhances type II activity (and indeed type I activity with the bicycles) (280-281) and provided dual inhibitors of type I and type II.
Abell et al. synthesized a number of tricyclic thiolactams (275-276), aryl acid (277), bicyclic lactams (278-281) and bicyclic thiolactam (282) and evaluated them in vitro as inhibitors of type I and type II steroid 5a-reductase (Table 31). Removal of two or more rings from 4-azasteroids resulted in a strong decrease of potency. The tricyclic thiolactams were found to be selective type I 5a-reductase inhibitors and in general were less active
Abell et al. synthesized a number of tricyclic thiolactams (275-276), aryl acid (277), bicyclic lactams (278-281) and bicyclic thiolactam (282) and evaluated them in vitro as inhibitors of type I and type II steroid 5a-reductase (Table 31). Removal of two or more rings from 4-azasteroids resulted in a strong decrease of potency. The tricyclic thiolactams were found to be selective type I 5a-reductase inhibitors and in general were less active
In vitro screening of compounds 266-274 against human 5a-reductase.
In vitro screening of compounds 266-274 against human 5a-reductase.
McCarthy and coworkers have recently synthesized a series of 4’-substituted 5-aryl pyridones along with corresponding 1-aryl- pyridone derivatives and tested them against 5a-reductase type I and type II expressed in transfected human embryonic kidney cells to examine structure activity relationship for the 4’ position in pyridones.
McCarthy and coworkers have recently synthesized a series of 4’-substituted 5-aryl pyridones along with corresponding 1-aryl- pyridone derivatives and tested them against 5a-reductase type I and type II expressed in transfected human embryonic kidney cells to examine structure activity relationship for the 4’ position in pyridones.
In vitro screening of compounds 275-282 against human 5a-reductase. Table 31
In vitro screening of compounds 275-282 against human 5a-reductase. Table 31
In vitro screening of compounds 286-292 against human 5a-reductase.
In vitro screening of compounds 286-292 against human 5a-reductase.
In vitro screening of compounds 308-317 against recombinant 5a-reductase I expressed in CHO cells.
In vitro screening of compounds 308-317 against recombinant 5a-reductase I expressed in CHO cells.
30. Mimics of 6-azasteroids: benzo[c] quinolinones Methyl esters of N-(dicyclohexyl)acetyl-piperidine-4- (benzylidene-4-carboxylic acid) (304) were designed and monitored for dual inhibition toward type II isozyme in BPH cell free preparation and for type I isozyme in DU 145 cells. Methyl esters, applied as hydrolytically stable precursor drugs to facilitate cell permeation, will yield the corresponding carboxylic acids as type II inhibitors after hydrolysis in the target organ. The esters themselves stable in human plasma and Caco-2 cells act as potent drug toward 5a-reductase type I. Thus, dual inhibition of 5a-reductase type I and type II can be achieved by applying a single parent compound [187].
30. Mimics of 6-azasteroids: benzo[c] quinolinones Methyl esters of N-(dicyclohexyl)acetyl-piperidine-4- (benzylidene-4-carboxylic acid) (304) were designed and monitored for dual inhibition toward type II isozyme in BPH cell free preparation and for type I isozyme in DU 145 cells. Methyl esters, applied as hydrolytically stable precursor drugs to facilitate cell permeation, will yield the corresponding carboxylic acids as type II inhibitors after hydrolysis in the target organ. The esters themselves stable in human plasma and Caco-2 cells act as potent drug toward 5a-reductase type I. Thus, dual inhibition of 5a-reductase type I and type II can be achieved by applying a single parent compound [187].
Fig. 7. SAR for A4-benzo[c] quinolizin-3-ones.
Fig. 7. SAR for A4-benzo[c] quinolizin-3-ones.
In vitro screening of compounds 318 and 319 against recombinant 5a-reductase | and II expressed in CHO cells. @ Mixture of A®(10a) / A 10(10a) isomers in 10:1 ratio.
In vitro screening of compounds 318 and 319 against recombinant 5a-reductase | and II expressed in CHO cells. @ Mixture of A®(10a) / A 10(10a) isomers in 10:1 ratio.
In vitro screening of compounds 320-325 against recombinant 5a-reductase I and Il expressed in CHO cells.
In vitro screening of compounds 320-325 against recombinant 5a-reductase I and Il expressed in CHO cells.
Invitro screening of compounds 326-330 against recombinant human 5a-reductas¢ land Il. Table 36
Invitro screening of compounds 326-330 against recombinant human 5a-reductas¢ land Il. Table 36
32. Non-steroidal aryl acids pound 322 was found to be the most potent dual inhibitor of the series with ICs59 values about 100 nM for both enzymes. Table 35
32. Non-steroidal aryl acids pound 322 was found to be the most potent dual inhibitor of the series with ICs59 values about 100 nM for both enzymes. Table 35
Some novel 9,10-dihydrophenanthrene-2-carboxylic acids (326-328) were prepared by formally removing D-ring from parent androstene carboxylic acid inhibitors and contrary to them, were found to be selective 5a-reductase | inhibitors. Introduction of a bromine atom at position 7 in compound 328 gave the most potent compound of the series. Substitution by chlorine at position 7 in compound 327 does not result in increase in potency as compared to unsubstituted compound 326. These compounds are supposed to interact with the positively charged enzyme-NADP* complex in an uncompetitive manner versus testosterone [195].
Some novel 9,10-dihydrophenanthrene-2-carboxylic acids (326-328) were prepared by formally removing D-ring from parent androstene carboxylic acid inhibitors and contrary to them, were found to be selective 5a-reductase | inhibitors. Introduction of a bromine atom at position 7 in compound 328 gave the most potent compound of the series. Substitution by chlorine at position 7 in compound 327 does not result in increase in potency as compared to unsubstituted compound 326. These compounds are supposed to interact with the positively charged enzyme-NADP* complex in an uncompetitive manner versus testosterone [195].
On removal of two or more rings from the parent steroidal com- pounds several aryl acids mimics of steroidal carboxylic acids have been synthesized (331-336). Hartmann et al. synthesized several N-substituted 4-(5-indolyl) benzoic acids but potent and selec- tive human 5a-reductase | inhibitors were not found from the series. Only compound 331 with ICsg value of 67 nM against human 5a-reductase I was the most potent inhibitor [197]. Similarly, com- pound 332 was found to possess ICs9 value of 680 nM [198].
On removal of two or more rings from the parent steroidal com- pounds several aryl acids mimics of steroidal carboxylic acids have been synthesized (331-336). Hartmann et al. synthesized several N-substituted 4-(5-indolyl) benzoic acids but potent and selec- tive human 5a-reductase | inhibitors were not found from the series. Only compound 331 with ICsg value of 67 nM against human 5a-reductase I was the most potent inhibitor [197]. Similarly, com- pound 332 was found to possess ICs9 value of 680 nM [198].
Epristeride 163) the selectivity toward 5a-reductase I was found to be lost in favor of an increased potency towards 5a-reductase II (Table 36) [196].
Epristeride 163) the selectivity toward 5a-reductase I was found to be lost in favor of an increased potency towards 5a-reductase II (Table 36) [196].
Fig. 8. SAR of benzophenone series. Igarashi et al. synthesized a new series of indole derivatives as potent human prostatic 5a-reductase inhibitors. Compounds (333-336) were found to be most potent among the series with 4-[(1-benzyl-1H-indol-5-yl) oxy]-3-chlorobenzoic acid 334 having an ICs9 value of 0.44 nM while 3-chloro-4-{1-(4-phenoxybenzoyl)- 1H-indol-5-ylloxy}benzoic acid 335 showed inhibitory activities for both human and rat prostatic 5a-reductase with ICs9 values of 2.1 and 73 nM, respectively [199].
Fig. 8. SAR of benzophenone series. Igarashi et al. synthesized a new series of indole derivatives as potent human prostatic 5a-reductase inhibitors. Compounds (333-336) were found to be most potent among the series with 4-[(1-benzyl-1H-indol-5-yl) oxy]-3-chlorobenzoic acid 334 having an ICs9 value of 0.44 nM while 3-chloro-4-{1-(4-phenoxybenzoyl)- 1H-indol-5-ylloxy}benzoic acid 335 showed inhibitory activities for both human and rat prostatic 5a-reductase with ICs9 values of 2.1 and 73 nM, respectively [199].
Screening of aryl carboxylate versus the human 5a-reductase isozymes by SmithKline-Beecham company led to the discovery of two series of selective and inhibitors based on benzop potent 5a-reductase II non-steroidal henone and indolecarboxylic acids skeleton. In benzophenone series of inhibitors the linker between the A- and B-rings proved to be crucial whereas linker between B- and C-rings was more to erant of variation. Both the A-ring carboxylic acid and C-ring are critical for activity. Compounds 337 and 338 were found to be most potent among the series with Kj app being 10 and 5 nM, res pectively. In indole series there was
Screening of aryl carboxylate versus the human 5a-reductase isozymes by SmithKline-Beecham company led to the discovery of two series of selective and inhibitors based on benzop potent 5a-reductase II non-steroidal henone and indolecarboxylic acids skeleton. In benzophenone series of inhibitors the linker between the A- and B-rings proved to be crucial whereas linker between B- and C-rings was more to erant of variation. Both the A-ring carboxylic acid and C-ring are critical for activity. Compounds 337 and 338 were found to be most potent among the series with Kj app being 10 and 5 nM, res pectively. In indole series there was
Takami et al. synthesized various indole derivatives with varied substituents on the a,B-unsaturated double bond and evaluated them for activity to inhibit rat prostatic 5a-reductase. Among the various derivatives they found
Takami et al. synthesized various indole derivatives with varied substituents on the a,B-unsaturated double bond and evaluated them for activity to inhibit rat prostatic 5a-reductase. Among the various derivatives they found
a strong preference for substitution at the 5- or 6-position of the indole ring. Compounds 339 and 340 were most active among the series with Kjapp being 10 and 40 nM, respectively The structure activity relationships of both the series are summarized as below (Figs. 8 and 9) [43,200].
a strong preference for substitution at the 5- or 6-position of the indole ring. Compounds 339 and 340 were most active among the series with Kjapp being 10 and 40 nM, respectively The structure activity relationships of both the series are summarized as below (Figs. 8 and 9) [43,200].
that (Z)-4-{2-[[3-[1-(4,4’-difluorobenzhydryl)indol-5-yl]-2- pentenoyl]-amino]phenoxy}butyric acid (341,KF20405) was the most potent compound having activity about 20 times greater than Finasteride (13) and an ICs value of 0.48 + 0.086 nM [201].
that (Z)-4-{2-[[3-[1-(4,4’-difluorobenzhydryl)indol-5-yl]-2- pentenoyl]-amino]phenoxy}butyric acid (341,KF20405) was the most potent compound having activity about 20 times greater than Finasteride (13) and an ICs value of 0.48 + 0.086 nM [201].
In 2002, various N-substituted 4’-biphenyl-4-carboxylic acids were synthesized by increasing the conformational flexibility using an ether linker between the steroidal A-C-ring mimetics and were tested against human and rat 5a-reductase type I and type II. Two compounds were found to be most potent with compound 345 showing an ICs value of 60nM while 346 showed an ICs9 value improved by a factor of 5 from 1.9 to 0.38 pM in comparison with the parent biphenyl compound 347 [204]. Sawada et al. synthesized a novel series of indolizinebutyric acids with various benzoyl substituents.FK687 (344) (S)-4-[1-[4- [[1-(4-isobutylpheny]) butyl] oxy] benzoyl] indolizin -3-yl] butyric acid displayed strongest in vitro inhibitory activity (IC59 =4.6 nM) against the human enzyme and in vivo inhibitory activity (IC59 = 1.7 nM) against the castrated young rat model among the series [203].
In 2002, various N-substituted 4’-biphenyl-4-carboxylic acids were synthesized by increasing the conformational flexibility using an ether linker between the steroidal A-C-ring mimetics and were tested against human and rat 5a-reductase type I and type II. Two compounds were found to be most potent with compound 345 showing an ICs value of 60nM while 346 showed an ICs9 value improved by a factor of 5 from 1.9 to 0.38 pM in comparison with the parent biphenyl compound 347 [204]. Sawada et al. synthesized a novel series of indolizinebutyric acids with various benzoyl substituents.FK687 (344) (S)-4-[1-[4- [[1-(4-isobutylpheny]) butyl] oxy] benzoyl] indolizin -3-yl] butyric acid displayed strongest in vitro inhibitory activity (IC59 =4.6 nM) against the human enzyme and in vivo inhibitory activity (IC59 = 1.7 nM) against the castrated young rat model among the series [203].
Baston et al. synthesized several 3,4-dihydro-naphthalene-2- carboxylic acids and evaluated them for 5a-reductase inhibitory activity. The most active inhibitors were 6-[3-(N,N-dicyclohexyl aminocarbonyl) phenyl]-3,4-dihydro-naphthalene-2-carboxylic acid (348) (IC59 =0.75 ~M, human type II; C59 = 0.81 ~M, human type I) and _ 6-[4-(N,N-diisopropylamino-carbonyl) phenyl] naphthalene-2-carboxylic acid (349) (ICs59=0.2¥M, human type II). The latter compound was shown to deactivate the enzyme in an uncompetitive manner (K;=90nM; Km, T=0.8-1.0 pM) similar to the steroidal inhibitor Epristeride (163) [205].
Baston et al. synthesized several 3,4-dihydro-naphthalene-2- carboxylic acids and evaluated them for 5a-reductase inhibitory activity. The most active inhibitors were 6-[3-(N,N-dicyclohexyl aminocarbonyl) phenyl]-3,4-dihydro-naphthalene-2-carboxylic acid (348) (IC59 =0.75 ~M, human type II; C59 = 0.81 ~M, human type I) and _ 6-[4-(N,N-diisopropylamino-carbonyl) phenyl] naphthalene-2-carboxylic acid (349) (ICs59=0.2¥M, human type II). The latter compound was shown to deactivate the enzyme in an uncompetitive manner (K;=90nM; Km, T=0.8-1.0 pM) similar to the steroidal inhibitor Epristeride (163) [205].
Kato and coworkers synthesized a series of pyrrole butyric acid derivatives and evaluated them for inhibitory activity on human and rat steroid 5a-reductase. In case of para-aminobenzoyl pyrrole derivatives (353-356), the introduction of ethyl (354) or isopropyl (355) at C-4 increased the activity [IC59 being 32 and 9.2, respec- tively], whereas the replacement with carboxyl (356) resulted in compounds with decreased inhibitory activity against human 5a-reductase enzyme, indicating steric restriction in the binding site of the enzyme. Compound with m-amino benzyl pyrrole (357) moiety was found to be more active than the corresponding para isomer (355) [ICs59 = 3.2 nM].
Kato and coworkers synthesized a series of pyrrole butyric acid derivatives and evaluated them for inhibitory activity on human and rat steroid 5a-reductase. In case of para-aminobenzoyl pyrrole derivatives (353-356), the introduction of ethyl (354) or isopropyl (355) at C-4 increased the activity [IC59 being 32 and 9.2, respec- tively], whereas the replacement with carboxyl (356) resulted in compounds with decreased inhibitory activity against human 5a-reductase enzyme, indicating steric restriction in the binding site of the enzyme. Compound with m-amino benzyl pyrrole (357) moiety was found to be more active than the corresponding para isomer (355) [ICs59 = 3.2 nM].
Igarashi et al. found a novel series of phenoxybenzoic acids derivatives as potent inhibitors of human prostatic 5a-reductase. It was found that introduction of a chloro (360), fluoro (361) or methoxy (362) group at 3-position of benzene ring (Rj ) leads to for- mation of compounds with high inhibitory activity with IC59 being 0.87, 0.67 and 0.56 nM, respectively [209].
Igarashi et al. found a novel series of phenoxybenzoic acids derivatives as potent inhibitors of human prostatic 5a-reductase. It was found that introduction of a chloro (360), fluoro (361) or methoxy (362) group at 3-position of benzene ring (Rj ) leads to for- mation of compounds with high inhibitory activity with IC59 being 0.87, 0.67 and 0.56 nM, respectively [209].
Ishibashi et al. synthesized a series of novel benzofuran deriva- tives with both carboxy and 5- or 6-diphenylmethylcarbamoyl groups and their inhibitory activities against rat and human testos- terone 5a-reductase were tested in vitro. The derivatives were more active against human type I enzyme than against type II enzyme. The 6-carbamoy] derivative such as 365 tended to be more potent than the 5-carbamoyl ones such as 366 with 365 being the most potent compound having ICs value of 37.9, 50 and 340 nM against rat, human type I and human type II isozymes [211]. Later, they also synthesized a series of 2-phenylbenzofuran derivatives with a carbamoyl, alkylamino, or alkyloxy group at the 5 or 6 position of the benzofuran ring. It was found that carbamoyl derivatives had more potent inhibitory activities than the alkylamino or alkyloxy derivatives against the rat enzyme and the 6-carbamoyl derivatives tended to be more potent than the 5-carbamoyl ones. The 6-carbamoyl and 6-alkylamino derivatives were found to be more potent inhibitors against human type I enzyme than type II but on whole compounds were found not to be selective [212]. The non-steroidal o-hydroxyaniline (261; ONO- 3805) was a weak compound in vitro versus human 5a-reductase II. It is a bi-substrate inhibitor in which the butanoic acid moiety is thought to be localized in the region of the phosphate group of NADPH and the lipophilic part could be orientated in the region of the steroidal C and D-ring, thus occupying the hydrophobic pocket of the enzyme. The fact that this compound acts as non- competitive inhibitor (versus T) and not as uncompetitive one, supports this hypothesis [173,213,214]. This prompted Pfizer to prepare the derivatives of 261 and subsequently C-3 acylindole (367) was prepared which had improved potency versus both human 5a-reductase enzymes. The benzodioxolane (368) adopts a similar minimum conformation to the ether (367) and proved to be a potent dual inhibitor of both 5a-reductase enzymes. In common with the steroidal carboxylic acid inhibitors, these compounds require the carboxylic acid moiety for potency and the 3-acylindole motif was found to be crucial for dual activity presumably by allowing access to both the conformations 369 and 370. The corresponding 2-methyl analog 371 which adopts conformation 370 due to the presence of methyl group on the
Ishibashi et al. synthesized a series of novel benzofuran deriva- tives with both carboxy and 5- or 6-diphenylmethylcarbamoyl groups and their inhibitory activities against rat and human testos- terone 5a-reductase were tested in vitro. The derivatives were more active against human type I enzyme than against type II enzyme. The 6-carbamoy] derivative such as 365 tended to be more potent than the 5-carbamoyl ones such as 366 with 365 being the most potent compound having ICs value of 37.9, 50 and 340 nM against rat, human type I and human type II isozymes [211]. Later, they also synthesized a series of 2-phenylbenzofuran derivatives with a carbamoyl, alkylamino, or alkyloxy group at the 5 or 6 position of the benzofuran ring. It was found that carbamoyl derivatives had more potent inhibitory activities than the alkylamino or alkyloxy derivatives against the rat enzyme and the 6-carbamoyl derivatives tended to be more potent than the 5-carbamoyl ones. The 6-carbamoyl and 6-alkylamino derivatives were found to be more potent inhibitors against human type I enzyme than type II but on whole compounds were found not to be selective [212]. The non-steroidal o-hydroxyaniline (261; ONO- 3805) was a weak compound in vitro versus human 5a-reductase II. It is a bi-substrate inhibitor in which the butanoic acid moiety is thought to be localized in the region of the phosphate group of NADPH and the lipophilic part could be orientated in the region of the steroidal C and D-ring, thus occupying the hydrophobic pocket of the enzyme. The fact that this compound acts as non- competitive inhibitor (versus T) and not as uncompetitive one, supports this hypothesis [173,213,214]. This prompted Pfizer to prepare the derivatives of 261 and subsequently C-3 acylindole (367) was prepared which had improved potency versus both human 5a-reductase enzymes. The benzodioxolane (368) adopts a similar minimum conformation to the ether (367) and proved to be a potent dual inhibitor of both 5a-reductase enzymes. In common with the steroidal carboxylic acid inhibitors, these compounds require the carboxylic acid moiety for potency and the 3-acylindole motif was found to be crucial for dual activity presumably by allowing access to both the conformations 369 and 370. The corresponding 2-methyl analog 371 which adopts conformation 370 due to the presence of methyl group on the
33. Bisubstrate inhibitors
33. Bisubstrate inhibitors
In vitro screening of compounds 367-371 against human 5a-reductase I and II and rat 5a-reductase. indole ring was found to be a selective inhibitor of 5a-reductase I (Table 37) [215]. FK-143 (372) 4-[3-[3-[bis (4-isobutylphenyl) methyl amino] benzoyl]-IH-indol-l-yl] butyric acid was disclosed by Sawada et al. as a potent dual inhibitor of both human 5a- reductase isozymes. It inhibited in vitro human and rat prostatic 5a-reductase in a dose-dependent manner with an ICs9 of 1.9 and 4.2nM, respectively, in a non-competitive fashion while in vivo showed potent inhibitory activity against castrated young rat model. This compound can be a potential drug for the treatment of benign prostatic hyperplasia [216-218]. Table 37
In vitro screening of compounds 367-371 against human 5a-reductase I and II and rat 5a-reductase. indole ring was found to be a selective inhibitor of 5a-reductase I (Table 37) [215]. FK-143 (372) 4-[3-[3-[bis (4-isobutylphenyl) methyl amino] benzoyl]-IH-indol-l-yl] butyric acid was disclosed by Sawada et al. as a potent dual inhibitor of both human 5a- reductase isozymes. It inhibited in vitro human and rat prostatic 5a-reductase in a dose-dependent manner with an ICs9 of 1.9 and 4.2nM, respectively, in a non-competitive fashion while in vivo showed potent inhibitory activity against castrated young rat model. This compound can be a potential drug for the treatment of benign prostatic hyperplasia [216-218]. Table 37
In search of novel non-steroidal mimics of steroidal inhibitors of 5a-reductase, 4-(2-phenylethyl)cyclohex-1-ene carboxylic acids were synthesized with different substituents in para position of the phenyl ring such as N,N-diisopropylcarbamoyl (373), phenyl,
In search of novel non-steroidal mimics of steroidal inhibitors of 5a-reductase, 4-(2-phenylethyl)cyclohex-1-ene carboxylic acids were synthesized with different substituents in para position of the phenyl ring such as N,N-diisopropylcarbamoyl (373), phenyl,
34. Miscellaneous non-steroidal inhibitors
34. Miscellaneous non-steroidal inhibitors
phenoxy, etc. They turned out to be good inhibitors of the human prostatic 5a-reductase isozyme II with 373 being the most potent one (ICs59 = 760 nM) [219]. Fan et al. evaluated a series of umbelliferone (7- hydroxycoumarin) derivatives as inhibitors of 5a-reductase I on LNCaP cells. The coumarin skeleton was considered as a mimetic of the proposed transition state of the natural substrate and as well as bioisostere of quinolin-2-one 1’,1’-dimethylallyloxycoumarin (374) showed potent inhibitory activity (IC59=1.3 ~M) for the 5a-reductase I. This was possibly a result of conformational effects of geminal dimethyl] group. 8-Allyl-7-hydroxycoumarin (375) also exhibited potent inhibitory activity (IC59 =0.99 iM) against 5a- reductase I enzyme. Introduction of a carbonyl group at 7-position (376) resulted in only a slight increase in 5a-reductase | inhibitory activity (IC59 =0.49 pM) [220].
phenoxy, etc. They turned out to be good inhibitors of the human prostatic 5a-reductase isozyme II with 373 being the most potent one (ICs59 = 760 nM) [219]. Fan et al. evaluated a series of umbelliferone (7- hydroxycoumarin) derivatives as inhibitors of 5a-reductase I on LNCaP cells. The coumarin skeleton was considered as a mimetic of the proposed transition state of the natural substrate and as well as bioisostere of quinolin-2-one 1’,1’-dimethylallyloxycoumarin (374) showed potent inhibitory activity (IC59=1.3 ~M) for the 5a-reductase I. This was possibly a result of conformational effects of geminal dimethyl] group. 8-Allyl-7-hydroxycoumarin (375) also exhibited potent inhibitory activity (IC59 =0.99 iM) against 5a- reductase I enzyme. Introduction of a carbonyl group at 7-position (376) resulted in only a slight increase in 5a-reductase | inhibitory activity (IC59 =0.49 pM) [220].
Chen et al. evaluated isoflavonoids as potential non-steroidal inhibitors of rat 5a-reductase by using the hypothetical phar- macophore of 5a-reductase. They proposed that although these compounds (379-382) were inhibitors of rat 5a-reductase in the
Chen et al. evaluated isoflavonoids as potential non-steroidal inhibitors of rat 5a-reductase by using the hypothetical phar- macophore of 5a-reductase. They proposed that although these compounds (379-382) were inhibitors of rat 5a-reductase in the
Due to the excellent estrogen receptor binding affinity of a series of 2’,6’-disubstituted 4-hydroxy-4’-hydroxymethy] biphenyl derivatives Lesuisse et al. designed various biphenyls as surrogates of the steroidal backbone. They hypothesized that by introducing appropriate substituents non-steroidal estrogens could be tai- lored into 5a-reductase inhibitors. Two compounds (377 and 378) emerged as potent type II 5a-reductase inhibitors with ICs9 being 71 and 9.8 nM, respectively [221].
Due to the excellent estrogen receptor binding affinity of a series of 2’,6’-disubstituted 4-hydroxy-4’-hydroxymethy] biphenyl derivatives Lesuisse et al. designed various biphenyls as surrogates of the steroidal backbone. They hypothesized that by introducing appropriate substituents non-steroidal estrogens could be tai- lored into 5a-reductase inhibitors. Two compounds (377 and 378) emerged as potent type II 5a-reductase inhibitors with ICs9 being 71 and 9.8 nM, respectively [221].
Hasoda et al. in 2007 designed and synthesized novel type I 5a-reductase inhibitors by using 3,3-diphenylpentane skeleton as a substitute for the usual steroid skeleton. 4-(3-(4-(N- Methylacetamido) phenyl) pentan-3-yl) phenyldibenzylcarbamate (383) was found to be a competitive 5a-reductase type | inhibitor with the ICsg value of 0.84 ~M among the series [223]. Finasteride (13) and Dutasteride (27) are the only two steroidal clinically used drugs that have evolved from nearly 40 years of research on steroids as 5a-reductase inhibitors but many com- pounds have shown promising results such as Epristeride (163) which is in clinical trials. Combination therapy of 5a-reductase inhibitors with various a-blockers like terazosin, alfuzosin and dox- azosin has been highly successful in the management of benign prostatic hyperplasia and combinations of 5a-reductase inhibitors with anti-inflammatory agents have been tried successfully and it is expected that this trend will continue. But the most challenging work will be the purification of 5a-reductase, for which all efforts have failed so far because of the unstable nature of the enzyme during purification, leading to a loss of activity. Ligand-based com- parative pharmacophore development using the known potent inhibitors could provide an insight into the structural requirements for the possible inhibitors of 5a-reductase [224]. Data obtained by such techniques could be used for developing more potent and selective inhibitors that can be manufactured by pharma- ceutical industries at a lower cost. Meanwhile, various classes of non-steroidal inhibitors have also emerged. It would be encour- aging to see if any of these molecules such as FK-143 (372) will be available for clinical use. Meanwhile, synthesis of steroidal and non- steroidal derivatives will continue in search of a more potent and less toxic inhibitor of 5a-reductase. The basic research described in this review article will assist in this process.
Hasoda et al. in 2007 designed and synthesized novel type I 5a-reductase inhibitors by using 3,3-diphenylpentane skeleton as a substitute for the usual steroid skeleton. 4-(3-(4-(N- Methylacetamido) phenyl) pentan-3-yl) phenyldibenzylcarbamate (383) was found to be a competitive 5a-reductase type | inhibitor with the ICsg value of 0.84 ~M among the series [223]. Finasteride (13) and Dutasteride (27) are the only two steroidal clinically used drugs that have evolved from nearly 40 years of research on steroids as 5a-reductase inhibitors but many com- pounds have shown promising results such as Epristeride (163) which is in clinical trials. Combination therapy of 5a-reductase inhibitors with various a-blockers like terazosin, alfuzosin and dox- azosin has been highly successful in the management of benign prostatic hyperplasia and combinations of 5a-reductase inhibitors with anti-inflammatory agents have been tried successfully and it is expected that this trend will continue. But the most challenging work will be the purification of 5a-reductase, for which all efforts have failed so far because of the unstable nature of the enzyme during purification, leading to a loss of activity. Ligand-based com- parative pharmacophore development using the known potent inhibitors could provide an insight into the structural requirements for the possible inhibitors of 5a-reductase [224]. Data obtained by such techniques could be used for developing more potent and selective inhibitors that can be manufactured by pharma- ceutical industries at a lower cost. Meanwhile, various classes of non-steroidal inhibitors have also emerged. It would be encour- aging to see if any of these molecules such as FK-143 (372) will be available for clinical use. Meanwhile, synthesis of steroidal and non- steroidal derivatives will continue in search of a more potent and less toxic inhibitor of 5a-reductase. The basic research described in this review article will assist in this process.
Related topics:
Benign Prostatic HyperplasiaLower Urinary Tract Symptoms
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