Simple Bi- and tricyclic inhibitors of human steroid 5α-Reductase

Article abstract of DOI:10.1016/S0960-894X(00)00368-1

A number of tricyclic thiolactams, bicyclic lactams, and bicyclic thiolactams have been prepared and evaluated in vitro as inhibitors of types 1 and 2 steroid 5α-reductase. The tricycles with an 8-chloro substituent in the C-ring are nM (IC₅₀) inhibitors of type 1 steroid 5α-reductase (SR). In all the cases studied, lactams are more potent than the corresponding thiolactams. Activity against type 2 SR is greatly enhanced by a styryl (or azo) substituent on the aryl ring of the tri- and bicycles and also a related tricyclic aryl acid. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00368-1

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1909±1911
Simple Bi- and Tricyclic Inhibitors of Human Steroid
5ꢀ-Reductase
Andrew D. Abell,a,* Maureen J. Prince,a Ann M. McNultyb and Blake L. Neubauerb
aDepartment of Chemistry, University of Canterbury, Christchurch, New Zealand
bLilly Research Laboratories, Indianapolis, IN 46285, USA
Received 9 May 2000; accepted 13 June 2000
AbstractÐA number of tricyclic thiolactams, bicyclic lactams, and bicyclic thiolactams have been prepared and evaluated in vitro
as inhibitors of types 1 and 2 steroid 5a-reductase. The tricycles with an 8-chloro substituent in the C-ring are nM (IC50) inhibitors
of type 1 steroid 5a-reductase (SR). In all the cases studied, lactams are more potent than the corresponding thiolactams. Activity
against type 2 SR is greatly enhanced by a styryl (or azo) substituent on the aryl ring of the tri- and bicycles and also a related
tricyclic aryl acid. # 2000 Elsevier Science Ltd. All rights reserved.
A number of di€erent classes of compounds are known
to inhibit steroid 5a-reductase (SR), an NADPH-
dependent enzyme that catalyses the bioreduction of
testosterone to the more potent androgen, dihydrotesto-
sterone (DHT).1 These inhibitors have been actively
pursued as potential therapeutic agents for the treatment
of pharmacological disorders associated with elevated
levels of DHT including benign prostatic hyperplasia
(BPH),1 some prostatic cancers,2 skin disorders such as
acne,3 male pattern baldness,4 and hirsutism.5 Initial
approaches to the design of inhibitors of SR employed
the steroid nucleus of the natural substrate of the
enzyme to provide mimics of the proposed enolate
intermediate in the bioreduction.1 This work led to
inhibitors of the type 16 and 2.7 More recently, a number
of simpler, nonsteroidal, inhibitors of SR have been
identi®ed (e.g. 38 and 4a).1b,9 A number of structural
similarities between the steroid and nonsteroidal series
have been noted, particularly in the A-ring functionality
(c.f. 1/4 and 2/3).1b,8 The structural factors that in¯u-
ence the potency and isozyme selectivity10 of the two
series have also been studied, although such studies on
the nonsteroidal compounds are still in their infancy. In
this paper we begin to assess some of these factors, in
particular the role of the B-ring and lactam function-
ality of the tricyclic analogues 4. These issues have been
addressed in the ®rst instance with the preparation and
testing, against types 1 and 2 SR, of the tricyclic
thiolactams 6, 7, 9, the bicyclic lactams 12, 16, 17, 20,
and the thiolactam 19. We also prepared and tested the
tricyclic aryl acid 11 to provide further insight into the
role of the styryl substituent in the related, tricyclic lac-
tam series of nonsteroidal compounds (see compounds
4b and 4c) where this group has been observed to pro-
vide dual isozyme inhibitors.11
Synthesis
The tricyclic thiolactams 6, 7 and 9 were conveniently
prepared by treating the corresponding lactones 5,9 4a,9
and 8,9 respectively, with [2,4-bis(4-methoxyphenyl)-1,3-
dithia-2,4-diphosphetane (Lawesson's reagent) (Scheme 1).
The tricyclic aryl acid 11 was prepared from the known
aryl bromide 108 by palladium mediated coupling,11
followed by ester hydrolysis (Scheme 1). The bicyclic
thiolactam 19 was prepared from 1612 by treatment
with Lawesson's reagent, Scheme 2. Compound 17 was
*Corresponding author. Tel.: +64-3-364-2818; fax: +64-3-364-2110;
e-mail: a.abell@chem.canterbury.ac.nz
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00368-1

1910
A. D. Abell et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1909±1911
Scheme 1. Reagents and conditions: (i) Lawesson's reagent, THF (5, re¯ux 6 h; 4, re¯ux 18 h; 8, rt 30 min); (ii) styrene, Pd(OAc)2, (o-tol)3P, Et3N,
AcCN, 100 ꢀC, 24 h; (iii) K2CO3, MeOH, H2O, re¯ux.
Scheme 2. Reagents and conditions: (i) KNO3, c H2SO4, rt (49%); (ii) PtO2, AcOH, H2, rt (51%): (iii) CuBr2, t-butylnitrite, AcCN, rt (18%); (iv)
Lawesson's reagent, THF, rt (87%); (v) nitrosobenzene, AcOH, rt (62%); (vi) styrene, Pd(OAc)2, (o-tol)3P, Et3N, AcCN, 100 ꢀC, 24 h.
Enzyme Inhibition
prepared as a mixture (contained <5% of the corre-
sponding cis-isomer by 1H NMR)13 by coupling the aryl
amine 14 with nitrosobenzene in acetic acid. Compound
14 was itself prepared from 1212 in a two step sequence
involving nitration followed by reduction with pal-
ladium oxide and hydrogen. The aryl amine 14 also
gave rise to the aryl bromide 15 and this in turn under
went palladium catalyzed coupling with styrene to give
the styryl bicyclic lactone 20 (Scheme 2).
The IC50 values (or % inhibition at constant concentra-
tion for the less active compounds) were determined
against types 1 and 2 SR14 and the results are given in
Table 1. An analysis of these results reveals some
important trends. First, the tricyclic thiolactams 6 and 7
are, like their lactam analogues,9 selective for type 1 SR.
However, in all cases thiolactams are less active than the
corresponding lactams (c.f. 5/6, 4a/7 and also 16/19). A
chloro substituent in the C-ring is favored for type 1
activity in both series (c.f. 4a/8 and 7/9) as is the absence
of a double bond in the B-ring (c.f. 5/4a and 6/7). It
should be noted that a steroid-based thiolactam has
been reported to be an inhibitor of rat prostatic SR.15
Table 1. Inhibition of types 1 and 2 SR
No.
Type 1 IC50 (nM)
Type 2 IC50 (nM)
or % inhibition
38
59
6
26a
120
377
17
20% @ 10 mM
Ð
13.2% @ 40 mM
Ð
180
21.6% @ 40 mM
Ð
19.9% @ 40 mM
340
13.5% @ 40 mM
12,350
579
14% @ 40 mM
617
The aryl acid 11 shows good dual isozyme inhibitory
properties with signi®cantly enhanced type 2 activity
compared to previously reported compounds of this
type (e.g. 3; type 1 Ki,app=26 nM, type 2 gave 20%
inhibition at 10 mM).8 However, 11 is still less active
than the equivalent bicyclic lactam 4b11 (IC50 type
1=23 nM, type 2=180 nM).
4a9
4b11
7
23
183
560
1450
152
2477
1690
302
3360
107
89
9
11
12
16
17
19
20
Bicyclic lactams, in general, would appear to be less
active against type 1 SR than the tricycles (c.f. 4a/16). In
contrast to the tricycles, a chloro substituent is not
optimum optimum for type 1 activity (c.f. 12, 16, and
aKi,app

A. D. Abell et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1909±1911
1911
20), however as before, a thiolactam produces a com-
pound with decreased type 1 activity as compared to a
lactam (c.f. 16/19). The results for 17 and 20 reinforce
an important, and apparently general observation that a
styryl (or azo) substituent dramatically enhances type 2
activity (and indeed type 1 activity with the bicycles).
Substituents of this type would appear to provide dual
inhibitors of types 1 and 2 SR in all series studied,
namely tricyclic lactams, aryl acids and bicyclic lactams.
It should also be noted that some bicyclic aryl acids
have been reported to be type 2 selective.16
A. H.; Brooks, J. R.; Berman, C. J. Med. Chem. 1986, 29,
2298.
7. Holt, D. A.; Levy, M. A.; Ladd, D. L.; Oh, H.-J.; Erb, J.
M.; Heaslip, J. I.; Brandt, M.; Metcalf, B. W. J. Med. Chem.
1990, 33, 937.
8. Abell, A. D.; Brandt, M.; Levy, M. A.; Holt, D. A. Bioorg.
Med. Chem. Lett. 1996, 6, 481.
9. (a) Jones, C. D.; Audia, J. E.; Lawhorn, D. E.; McQuaid,
L. A.; Neubauer, B. L.; Pike, A. J.; Pennington, P. A.; Stamm,
N. B.; Toomey, R. E.; Hirsch, K. S. J. Med. Chem. 1993, 36,
421. (b) Abell, A. D.; Erhard, K. F.; Yen, H.-K.; Yamashita,
D. S.; Brandt, M.; Mohammed, H.; Levy, M. A.; Holt, D. A.
Bioorg. Med. Chem. Lett. 1994, 4, 1365.
10. Two isozymes of steroid 5a-reductase, di€ering in their
pattern of tissue distribution and with distinct biochemical
and pharmacological properties, have been identi®ed. Jenkins,
E. P.; Andersson, S.; Imperato-McGinley, J.; Wilson, J. D.;
Russell, D. W. J. Clin. Invest. 1992, 89, 293.
11. Smith, E. C. R.; McQuaid, L. A.; Goode, R. L.; McNulty,
A. M.; Neubauer, B. L.; Rocco, P.; Audia, J. E. Bioorg. Med.
Chem. Lett. 1998, 8, 395.
In conclusion, a number of tricyclic thiolactams, bicyc-
lic lactams and bicyclic thiolactams have been prepared
and evaluated in vitro as inhibitors of types 1 and 2
steroid 5a-reductase. We have shown that similar sub-
stituent e€ects operate throughout these compounds
and also the tricyclic aryl acids 3 and 11. It should also
be noted that the opportunity exists to photoswitch 17
between its trans and cis forms as a potential means to
modulate its types 1 and 2 activity.17 Finally, com-
pounds 11, 17 and 20 are good dual isozyme inhibitors
in spite of their simple structure relative to previously
reported inhibitors of SR.1 Even more potent com-
pounds of this type should be able to be prepared by
further ®ne-tuning the substituents.
12. Shen, T.; Witzel, B. E. US Patent 808,660, 1969. Julia, M.;
Si€ert, O.; Bagot, J. Bull. Soc. Chim. Fr. 1968, 3, 1000.
13. Photolysis of this mixture gave a 13:87 mixture of 17 and 18.
3
3
14. Type 1 assays: The conversion of H-labelled T into H-
labelled DHT using type 1 SR isolated from human scalp was
measured as previously described (see McNulty, A. M.; Audia,
J. E.; Bemis, K. G.; Goode, R. L.; Rocco, V. P.; Neubauer, B.
L. J. Steroid Biochem. Mol. Biol. 2000, 72, 13). In short, the
test compounds were dissolved in methanol to 10, 100, 1000, and
10,000 nM concentrations. Labeled T (80 nM, 8.07Â10 3 mCi
speci®c activity 92.41 Ci/mmol) and unlabelled T (0.92 mM)
were combined with the test compounds to give a total sub-
strate concentration of 1.0 mM in a volume of 200 mL. The
assay was initiated by the addition of 0.015±0.025 mg of type 1
SR homogenate to the substrate and the mixture was then
incubated for 1 h at 37 ꢀC. Substrates and metabolites were
quanti®ed by HPLC separation and in-line ¯ow radioactivity
detection of the labelled androgens.
Acknowledgements
This work was supported by a research grant from the
Royal Society of New Zealand Marsden Fund.
References and Notes
1. For reviews see: (a) Holt, D. A.; Levy, M. A.; Metcalf, B.
W. In Advances in Medicinal Chemistry; Maryano€, B. E.,
Maryano€, C. A., Eds.; JAI: London, 1993; Vol 2, pp 1±29.
(b) Abell, A. D.; Henderson, B. R. Curr. Med. Chem. 1995, 2,
583. (c) Kenny, B.; Ballard, S.; Blagg, S.; Fox, D. J. Med.
Chem. 1997, 40, 1293.
2. Lamb, J. C.; Levy, M. A.; Johnson, R. K.; Isaacs, J. T.
Prostate 1992, 21, 15.
3. Sansone, G. L.; Reisner, R. M. J. Invest. Dermatol. 1971,
56, 366.
4. Diani, A. R.; Mulholland, M. J.; Shull, K. L.; Kubicek, M.
F.; Johnson, G. A.; Schostarez, H. J.; Brunden, M. N.; Buhl,
A. E. J. Clin. Endocrinol. Metab. 1992, 74, 505.
5. Kuttenn, F.; Mowszowicz, I.; Shaison, G.; Mauvais-Jarvis,
P. J. Endocrinol. 1977, 75, 83.
Type 2 assay: This was carried out using SR isolated from
human prostate tissues (11.34 mg per reaction). T was added
(50 nM, speci®c activity 40.3 Ci/mmol) and the mixture was
incubated at 25 ꢀC for 1 h. The inhibitors were prepared and
tested as described for the type 1 assay. A type 1 speci®c inhi-
bitor was analysed for activity against the type 2 enzyme pre-
paration and it showed no detectable inhibition at 1 mM
concentration. The activity of both assays was calibrated using
known type 1 and type 2 inhibitors.
15. Rasmusson, G. H.; Reynolds, G. F.; Utne, T.; Jobson, R.
B.; Primka, R. I.; Berman, C.; Brooks, J. R. J. Med. Chem.
1984, 27, 1690.
16. Holt, D. A.; Yamashita, D. S.; Konialian-Beck, A. L.;
Luengo, Y. I.; Abell, A. D.; Bergsma, D. J.; Levy, M. A. J.
Med. Chem. 1995, 38, 13.
6. Ramusson, G. H.; Reynolds, G. F.; Steinberg, N. G.;
Walton, E.; Patel, G. F.; Liang, T.; Cascieri, M. A.; Cheung,
17. In support, compounds 4b and 4c show di€erent isozyme
selectivity (see ref 11).