Biphenyls as surrogates of the steroidal backbone. Part 2: Discovery of a novel family of non-steroidal 5-α-reductase inhibitors

Article abstract of DOI:10.1016/S0960-894X(01)00268-2

A new family of non-steroidal 5-α-reductase inhibitors was designed by replacing the steroid skeleton of an inhibitor related to estrone by a biphenyl moiety. This hypothesis originated from the reported estrogenic activity of a few biphenyl compounds (see Part 1 of this paper; Lesuisse et al. Bioorg. Med. Chem. Lett. 2001, 11, 1709). Two compounds turned out to be potent type 2 5-α-reductase inhibitors with IC₅₀'s of inhibition in the nanomolar range. These are to our knowledge amongst the most potent non-steroidal 5-α-reductase inhibitors described to date.

Full text of DOI:10.1016/S0960-894X(01)00268-2

Bioorganic & Medicinal Chemistry Letters 11 (2001) 1713–1716
Biphenyls as Surrogates of the Steroidal Backbone.
Part 2: Discovery of a Novel Family of Non-steroidal
5-ꢀ-Reductase Inhibitors
Dominique Lesuisse,a,* Jean-Francois Gourvest,b Eva Albert,a Bernard Doucet,b
Catherine Hartmann,b Jean-Michel Lefrancois,a Sophie Tessier,a Bernadette Trica
and Georges Teutscha
aMedicinal Chemistry, Aventis, 102 route de Noisy, 93235 Romainville Cedex, France
bBone Diseases Group, Aventis, 102 route de Noisy, 93235 Romainville Cedex, France
Received 31 January 2001; revised 28 March 2001; accepted 18 April 2001
Abstract—A new family of non-steroidal 5-a-reductase inhibitors was designed by replacing the steroid skeleton of an inhibitor
related to estrone by a biphenyl moiety. This hypothesis originated from the reported estrogenic activity of a few biphenyl com-
pounds (see Part 1 of this paper; Lesuisse et al. Bioorg. Med. Chem. Lett. 2001, 11, 1709). Two compounds turned out to be potent
type 2 5-a-reductase inhibitors with IC50’s of inhibition in the nanomolar range. These are to our knowledge amongst the most
potent non-steroidal 5-a-reductase inhibitors described to date. # 2001 Elsevier Science Ltd. All rights reserved.
Introduction
The objective of this paper is to describe the synthesis of
this new series of compounds and the results we have
obtained using this approach.
Steroid 5-a-reductase (EC 1.3.99.5) is the enzyme that
catalyzes the conversion of testosterone to di-hydro-
testosterone (DHT), the most potent prostatic andro-
gen. Finasteride 1,1 one of the first described inhibitors
of this enzyme, is currently marketed worldwide as a
treatment for BPH. A few years ago, Holt and co-
workers described a new class of steroidal inhibitors
of 5-a-reductase, 2, incorporating the estradiol ske-
leton.2 Based on these new potent estrone-derived
inhibitors of the 5-a-reductase, we hypothesized that
by introducing appropriate substituents non-steroidal
estrogens could be tailored into 5-a-reductase inhibi-
tors. We had recently identified a new family of estro-
gens based on the biphenyl scaffold.3 The best
compounds in these series were the 20,60-dibromo- and
dichlorobiphenyls 3 and 4. Based on these findings, we
speculated that similar compounds where the 4-hydroxy
and the 40-hydroxymethyl groups would be replaced by
4-carboxylic acid and 40-carboxamidomethyl groups,
respectively, as in 5 could potentially be good 5-a-
reductase inhibitors.
Chemistry4 and Biology5
We decided to first check the validity of the hypothesis
by synthesizing the simplest derivative of 5 incorporat-
ing the desired functionalities (X=H, Y=—). Diiso-
propyl 4-hydroxy benzamide 66 was transformed into its
triflate7 and condensed with tolyl boronic acid using
standard conditions.8 The methyl group of 7 was
*Corresponding author. Fax: +33-1-4991-5087; e-mail: dominique.
lesuisse@aventis.com
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00268-2

1714
D. Lesuisse et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1713–1716
oxidized using potassium permanganate in pyridine9 to
afford the desired carboxylic acid 8 with a good yield
(Scheme 1). Even this simple compound proved to inhi-
bit human prostate 5-a-reductase5 by about 30% at
1 mM(compared to Finasteride 110 (IC50=1.2 10À8 M)
and 211 (IC50=10À9 M)) (Table 1).
linker between the biphenyl and the amide portion. The
compounds 17–19 were obtained uneventfully.14 Of all
unsubstituted biphenyl derivatives (Table 2), 19 inhib-
ited the enzyme best and therefore we decided to keep
this moiety for reinvestigating the biphenyl substitution.
In view of our initial hypothesis, we invested again most
of our effort into the synthesis of ortho disubstituted
halogen derivatives of 19. To this end, we used biphenyl
intermediates we had prepared for our estrogen binding
studies.3 Protected ortho halogenobiphenyls 20–25
incorporating a carboxylic acid function precursor were
transformed by alkylation of the deprotected phenol
with diisopropylamino-1-bromoacetamide 26. Oxida-
tion or hydrolysis gave the desired carboxylic acids 27–
32 (Scheme 3, Table 3). The new derivatives were eval-
uated against 5-a-reductase in comparison with 19. The
results confirmed the trend seen with derivatives 12–16.
No improvement of the inhibition properties was seen
upon introduction of any halogen or methyl group in
the ortho, ortho0 position of either aromatic ring (Table
5).
Comforted by this first result, we embarked on the
synthesis of an analogue of 8 incorporating the required
ortho disubstitution (5, X=Br, Y=—). The synthesis
proved to be not as straightforward as envisaged. The
way we finally succeeded in obtaining the desired com-
pound was by the Ullmann coupling12 of diisopropyl 4-
chloro-3,5-dinitro benzamide 9 with methyl 4-iodo-
benzoate, followed by reduction, diazotation13 and
hydrolysis to give desired compound 12 (Scheme 2). The
dinitro biphenyl 10 was also elaborated into the nitro-
and amino-derivatives 14 and 16 and the iodo-deriva-
tives 13 and 15 (see Table 1) using methods reported
previously.3
To our surprise, none of the ortho disubstituted
biphenyls 12–16 gave any detectable inhibition of the
5-a-reductase at 1 mM(Table 1).
Evidently, the criteria for estrogen receptor binding
affinity of 4-hydroxy-40-hydroxymethyl biphenyls which
very stringently required 20,60-disubstitution of the sec-
ond aromatic ring mainly with chlorine and bromine,
were not determinant for 5-a-reductase inhibition. In
the absence of structural information on the active site
of 5-a-reductase, we embarked on a wider exploration
of the biphenyl substitution to improve the inhibition
Because our experience in the field of biphenyls and
estrogens3 had taught us that the chain mimicking the
17-position of the steroid nucleus had to be tailored to
the appropriate length, we evaluated the inhibition
behaviour of compounds obtained by varying the Y
Scheme 1.
Scheme 2.
Table 1. 5-a-Reductase inhibition by 20, 60-disubstituted biphenyl
derivatives of 8
Table 2. Influence of the length of the side chain on 5-a-reductase
inhibition
X
Y
Compound
% Inhib. (10À6 M)
H
Br
NO2
H2N
I
H
Br
I
NH2
I
NO2
8
32.5
X
Compound
% Inhib. (10À6 M)
12
13
14
15
16
0
0
0
0
0
—
CH2
CH(Me)
OCH2
8
32.5
37
26.9
57.5
17
18
19
NO2

D. Lesuisse et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1713–1716
1715
Scheme 3.
Table 3. Synthesis of o-disubstituted biphenyl derivatives 27–32 from 20–25
Starting
compound
R
X
Y
P
Conditions (yield)
Compound
20
21
22
23
24
25
CH2OH
CHO
CHO
COOMe
COOMe
CHO
F
Cl
Me
—
Cl,H
CF3,H
—
—
—
Cl
—
—
Bn
tBuPh2Si
tBuPh2Si
tBuMe2Si
Bn
(1) Jones (76%); (2) H2/Pd/C (93%); (3) 26/NaOH/DMSO (49%)
(1) TBAF (Q); (2) 26/NaH/THF (68%); (3) NaClO2/H2NSO3H (61%)
(1) TBAF(Q); (2) 26/NaOH/DMSO (75%); (3) NaClO2/H2NSO3H (71%)
(1) TBAF(Q); (2) 26/NaOH/DMSO (20%)
27
28
29
30
31
32
(1) H2/Pd/C (99%); (2) 26/NaOH/DMSO (15%)
(1) H2/Pd/C (Q); (2) Jones (95%); (3) 26/NaOH/DMSO (16%)
Bn
pattern. Some of the chemistry and results are summar-
ized hereunder. Hydroquinones 33 and 34 were trans-
formed into suitably functionalized candidates by
sequential reactions with diisopropylamino-1-bromo-
acetamide 26 and triflic anhydride followed by biphenyl
coupling reactions of the resulting triflates with 4-for-
mylphenyl boronic acid. Oxidation of the resulting
aldehydes gave carboxylic acids 37 and 38. The same
sequence of reactions was undertaken for the 4-bromo-
phenol derivatives 35 and 36 where coupling was per-
formed right after alkylation with diisopropylamino-1-
bromoacetamide 26 to afford new compounds 39 and 40
(Scheme 4, Table 4).
Table 5. 5-a-Reductase inhibition by polysubstituted biphenyl deri-
vatives of 19
R1
R2
R3
R4
IC50
Compound
H
F
Cl
M
—
Cl,H
CF3,H
—
—
—
—
—
—
—
—
—
—
—
8.3.10À7
>10À6
>10À6
>10À6
>10À6
8.7.10À7
5.7.10À7
—
M
M
19
27
28
29
30
31
32
37
38
39
40
41
42
1
M
M
M
M
M
e
—
—
—
—
—
Cl
—
—
—
—
2-Ethyl-1,4-hydroquinone was converted to both com-
pounds 41 and 42 by an analogous sequence of reac-
tions (data not shown).
–CH¼CH–CH¼CH–
—
IPr
F
—
—
CN,H
—
—
CN
IPr
NO2
—
—
7.1.10À8
9.8.10À9
M
M
Et,H
—
2.10À6
M
All new compounds displayed inhibition of 5-a-reductase
to some extent (Table 5). Substitution of the first aromatic
ring brought about no increase of inhibition compared to
the unsubstituted compound (Table 5, cf. 27–29, 31, and
—
Et
3.5.10À7
M
4.10À8
2.10À9
M
M
2
Scheme 4.
Table 4. Synthesis of polysubstituted biphenyl derivatives 37–40 from 33–36
Starting
compound
R1
R2
R3
X
Conditions (yield)
Compound
33
34
–CH¼CH–CH¼CH–
—
—
OH
OH
(1) KH/DMF (38%); (2) 2,6-tBu2Pyridine/CH2Cl2 (69%);
(3) (51%); (4) Jones/acetone (24%)
(1) NaH/DMF (60%); (2) IPr2Net/CH3CN (50%); (3) (13%);
(4) PDC/DMF (40%)
37
38
CN
CN
35
36
iPr
NO2
—
—
iPr
F
Br
Br
(1) NaH/DMF (96%); (3) (30%); (4) Ag2O/NaOH 1 N/THF (14%)
(1) MeOK/DMSO (51%); (3) (17%); (4) Ag2O/NaOH 1 N/THF (88%)
39
40

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D. Lesuisse et al. / Bioorg. Med. Chem. Lett. 11 (2001) 1713–1716
32 with 19). Furthermore monosubstitution at the ortho
position of the second aromatic ring had a detrimental
effect on the inhibition (cf. 37, 38, and 41 to 19). Finally,
introduction of substituents ortho to the amide function
had a dramatic effect on the inhibition (39, 40). A fluorine
and a nitro group in these positions improved the inhi-
bition by 100-fold over the unsubstituted derivative 19.
These new compounds now displayed better inhibition
than the reference Finasteride (see Table 5).
Acknowledgements
The authors wish to thank our colleagues and their col-
laborators in the Physical Chemistry Department and
the Analytical Laboratory for their help in recording
and interpreting the spectra and performing the ele-
mental analysis, respectively.
References and Notes
Finally, we tried to further improve 40 by replacing the
diisopropylamide moiety by a trityl amide. Frye had
described this as the optimal side chain for 5-a-reduc-
tase inhibition by 6-azasteroid derivatives.15 However,
in our case the resulting compound 43 was about 10-
fold less active than the diisopropylamide analogue
(IC50=92 nMvs 9.8 nM).
1. Gormley, G. H.; Stoner, E.; Bruskewitz, R. C.; Imperato-
McGinley, J.; Walsh, P. C.; McConnel, J. D.; Andriole, G. L.;
Geller, J.; Bracken, B. R.; Tenover, J. S.; Darracott-Vaughan,
E.; Pappas, F.; Taylor, A.; Binkowitz, B.; Ng, J. N. Engl. J.
Med. 1992, 327, 1185.
2. Holt, D. A.; Levy, M. A.; Oh, H.-J.; Erb, J. M.; Heaslip,
J. I.; Brandt, M.; Lan-Hargest, H.-Y.; Metcalf, B. W. J. Med.
Chem. 1990, 33, 943.
3. Lesuisse, D.; Albert, E.; Bouchoux, F.; Cerede, E.; Lefran-
´ `
cois, J. M.; Levif, M. O.; Philibert, D.; Tessier, S.; Tric, B.;
Teutsch, G. Bioorg. Med. Chem. Lett. 2001, 11, 1709.
4. All final compounds had full analyses (NMR, IR, SM)
along with correct elemental analyses.
5. A homogenate of type 2 5-a-reductase was prepared from
human prostates according to: Liang, T.; Cascieri, M. A.;
Cheung, A. H.; Reynolds, G. F.; Rasmusson, G. H. Endocri-
nology. 1985, 117, 571. The enzymatic activity was determined
with an HPLC apparatus and an on-line detector (Flo-one)
according to: Le Goff, J. M.; Martin, P. M. In Progress in
HPLC, Vol 3: Flow-through Radioactive Detectors in HPLC;
Parvey, H., Ed.; International Science: Utrecht, 1988; pp 79–85.
6. Synthesized from 4-hydroxybenzoic acid using thionyl
chloride in dichloromethane followed by diisopropylamine.
After a basic work up (ccNaOH) the expected compound was
precipitated with 6 N HCl (74% yield).
7. Echavarren, A. M.; Stille, J. K. J. Am. Chem. Soc. 1987,
109, 5478.
8. Huth, A.; Beetz, I.; Schumann, I. Tetrahedron 1989, 45, 6679.
9. Fatiadi, A. J. Synthesis 1987, 85.
10. Finasteride was extracted from the formulated Chibro-
Proscar1.
11. 2 was synthesized as described in the literature: see ref 3.
12. For a general review on Ullmann coupling, see, for
instance: Fanta, P. E. Synthesis 1974, 1, 9.
Conclusion
Our study was initiated by our initial observations of
the excellent estrogen receptor binding affinity of a ser-
ies of 20,60-disubstituted 4-hydroxy-40-hydroxymethyl
biphenyl derivatives.1 This observation led us to hypo-
thesize that a similar biphenyl scaffold suitably tailored
could be a useful steroid replacement in other areas of
steroid receptors and biosynthesis. Our study demon-
strates that this is at least the case in the field of dihy-
drotestosterone biosynthesis with the discovery of a
potent non-steroidal inhibitor of the type 2 5-a-reduc-
tase enzyme. Compound 40 is amongst the most potent
non-steroidal inhibitor of the enzyme reported. Note-
worthy in this regard is a publication by Abell of
inhibitors somewhat chemically related like 44 and
devoid of inhibitory activity on type 2 isoenzyme.16
The same team was also able to identify chemically
related inhibitors like 45 by high throughput screen-
ing.17
13. Beck, J. R.; Gajewski, R. P.; Lynch, M. P.; Wright, F. L.
J. Heterocycl. Chem. 1987, 24, 267.
14. Synthesis described elsewhere.
15. Frye, S. V.; Haffner, C. D.; Maloney, P. R.; Mook, R. A.,
Jr.; Dorsey, G. F., Jr.; Hiner, R. N.; Batchelor, K. W.; Bram-
son, H. N.; Stuart, J. D.; Schweiker, S. L.; Van Arnold, J.;
Bickett, D. M.; Moss, M. L.; Tian, G.; Unwalla, R. J.; Lee, F.
W.; Tippen; T. K.; James, M. K.; Grizzle, M. K.; Long, J. E.;
Schuster, S. V. J. Med. Chem. 1993, 36, 4313.
16. Abell, A. D.; Brandt, M.; Levy, M. A.; Holt, D. A.
Bioorg. Med. Chem. Lett. 1996, 6, 481.
A compound like 40 could be of value in the treat-
ment of diseases related to the function of this
enzyme.
17. Holt, D. A.; Yamashita, D. S.; Konialan-Beck, A. L.;
Luengo, J. I.; Abell, A. D.; Bergsma, D. J.; Brandt, M.; Levy,
M . A.J. Med. Chem. 1995, 38, 13.