3,3-Diphenylpentane skeleton as a steroid skeleton substitute: Novel inhibitors of human 5α-reductase 1

Article abstract of DOI:10.1016/j.bmcl.2007.07.039

We designed and synthesized novel type 1 5α-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)phenyl dibenzylcarbamate (11k) is a competitive 5α-reductase inhibitor with the IC₅₀ value of 0.84 μM.

Full text of DOI:10.1016/j.bmcl.2007.07.039

Bioorganic & Medicinal Chemistry Letters 17 (2007) 5414–5418
3,3-Diphenylpentane skeleton as a steroid skeleton substitute:
Novel inhibitors of human 5a-reductase 1
Shinnosuke Hosoda and Yuichi Hashimoto*
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
Received 27 June 2007; revised 4 July 2007; accepted 11 July 2007
Available online 31 July 2007
Abstract—We designed and synthesized novel type 1 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)phenyl dibenzylcarbamate (11k) is a competitive 5a-
reductase inhibitor with the IC50 value of 0.84 lM.
Ó 2007 Elsevier Ltd. All rights reserved.
Steroid hormones regulate a wide range of physiological
processes, including reproduction, development, and
homeostasis, by binding to and activating the nuclear
receptors (NRs).1 Testosterone, which is biosynthesized
from cholesterol, is converted by 5a-reductase to the
more active metabolite, 5a-dihydrotestosterone (DHT),
which is considered to play a major role in androgenic
signal transduction.2 Since DHT production aggravates
several diseases, including prostate cancer,3,4 benign
Figure 1. Structures of finasteride (1) and dutasteride (2).
prostatic hyperplasia (BPH)5 and androgenic alope-
cia,6,7 several 5a-reductase inhibitors have been devel-
oped for the treatment of these disorders.8–10
owing to cross-reactivity with other steroid hormone
Recently, two types of human 5a-reductases have been
identified.11,12 Type 1 5a-reductase (5aR-1) is expressed
predominantly in liver and sebaceous glands of skin,
whereas type 2 5a-reductase (5aR-2) is found in pros-
tate, seminal vesicles, epididymis, liver, and hair folli-
cles. Interestingly, some human prostate cancer cell
lines, DU-145 and LNCaP, express only 5aR-1.13,14
5a-Reductase inhibitors down-regulate DHT and sup-
press prostate cancer cell proliferation.15 Therefore,
5aR-1 inhibitors may selectively inhibit the growth of
prostate tumors.
receptors, including progesterone receptor (PR).18
Moreover, steroidal compounds are rapidly modified
by several steroid-metabolizing enzymes. Therefore,
development of 5aR-1 inhibitors with a non-steroidal
skeleton is expected to be an effective strategy.
In our previous study, we showed that 3,3-diphenylpen-
tane (DPP) derivatives act as ligands of several NRs.
Typical examples are shown in Figure 2, that is, a vita-
min D receptor (VDR) agonist 3,19,20 an androgen
receptor (AR) antagonist 4,19,20 a farnesoid X receptor
(FXR) agonist 5,21 and a PR antagonist 6.22
Steroidal 5a-reductase inhibitors, including finasteride
(1) and dutasteride (2) (Fig. 1), are used clinically to
treat BPH.16,17 However, undesired adverse effects occur
Because natural ligands of these NRs have steroidal (or
secosteroidal) structure, it is suggested that the DPP
skeleton may act not only as a multi-template for NR li-
gands, but also as a steroid skeleton substitute that
would be recognized by steroid-metabolizing enzymes.
In this paper, we report the synthesis of novel 5aR-1
inhibitors developed based on a DPP skeleton.
Keywords: 3,3-Diphenylpentane; Steroid; 5a-Reductase; Inhibitor.
*
Corresponding author. Tel.: +81 3 5841 7848; fax: +81 3 5841
8495; e-mail: hashimot@iam.u-tokyo.ac.jp
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.07.039

S. Hosoda, Y. Hashimoto / Bioorg. Med. Chem. Lett. 17 (2007) 5414–5418
5415
Figure 2. Typical NR ligands with a DPP skeleton.
We designed a candidate lead compound 8a with a DPP
skeleton based on the structure of 4-MA (7) (Fig. 3), a
potent 5aR-1 inhibitor (at least in vitro), which is struc-
turally related to finasteride (1) and dutasteride (2).23
The N-methyl-N-phenylacetamide moiety of 8a was cho-
sen as a mimic of the steroid A-ring structure of 4-MA
(7). The DPP skeleton possessing an amino group was
synthesized as previously described (Scheme 1).19,20
bated with LNCaP cells for 18 h, and metabolites
were extracted with Et2O. The metabolite mixture
thus obtained was separated by means of thin layer
chromatography (Merck 25 TLC plates silica gel 60
F254) with ethyl acetate/hexane (1:1 v/v). The radioac-
tivity of each spot on the plate was measured with a
bioimaging analyzer (BAS-2000, Fuji Film, Tokyo,
Japan). 5aR-1-inhibitory activity was calculated from
the ratio of the radioactivities of starting material
([14C]A-en) and its reduced metabolite 5a-andro-
standione ([14C]A-an). The assay was performed in
duplicate or triplicate, and the mean values were ta-
ken. The experiments were repeated at least two
times, and a typical set of data was shown in this
paper.
The inhibitory potency of the prepared compounds
toward human 5aR-1 was evaluated by the method
described by Picard et al.,24 except that human pros-
tatic carcinoma LNCaP cells14 were used instead of
human prostatic carcinoma DU 145 cells. Briefly,
[4-14C]androstenedione ([14C]A-en) (50 nM) was incu-
Figure 3. Molecular design of a DPP type 5aR-1 inhibitor.
Scheme 1. Reagents and conditions: (a) 3-pentanone, methanesulfonic acid, 3 d, 36–53%; (b) 2-R2-aniline, neat, 180 °C, 3 h, 41–85%; (c) NaH,
diethylcarbamoyl chloride, DMF, 2 h; (d) Ac2O, pyridine, CH2Cl2, 1 h, 44–90% in two steps; (e) NaH, MeI, DMF, 18 h, 75–100%.

5416
S. Hosoda, Y. Hashimoto / Bioorg. Med. Chem. Lett. 17 (2007) 5414–5418
Table 1. 5aR-1 inhibitory activity of DPP derivatives
Table 2 summarizes the structure–activity relationships
(SAR) of the 8d derivatives, 10a–f. The prepared
derivatives possessing dialkyl (10a,10b) or cycloalkyl
(10c–f) groups were less potent than 8d. This feature
of the SAR is similar to that found for derivatives
of VDR ligand (3), AR ligand (4), and FXR ligand
(5). The results suggest that the diethyl–diphenyl moi-
ety (i.e., a DPP skeleton) is an appropriate substitute
for a steroid skeleton.
Compound
R1
R2
R3
Inhibition (%)
at 10 lM
Thus, we focused our attention on the synthesis and
SAR of the side chain analogs (Scheme 3). The diethylc-
arbamoyl group of 8d was changed to several other sub-
stituents as shown in Table 3. Introduction of bulky
groups (11b–c,11e–f) resulted in more potent inhibitory
activity, as compared with 8d. On the other hand,
groups possessing an additional heteroatom (11g,11h)
resulted in weaker inhibitory activity.
9a
8a
8b
8c
8d
Me
Me
Me
H
Me
Me
H
H
17
22
56
25
57
Me
Me
Me
Me
Me
H
H
In our assay system, the IC50 value for inhibition of
5aR-1 activity of finasteride (1) was calculated to be
24 nM. This value is consistent with the reported IC50
value (39 nM) of finasteride (1).24 The designed DPP-
based compound 8a and its synthetic precursor 9a
showed only slight inhibition, 22% and 17% at 10 lM,
respectively (Table 1).
Based on these results, more bulky and hydrophobic
groups were introduced (Table 3, 11i–l). The inhibitory
activity of these compounds was screened at the lower
concentration of 1 lM. The chain-elongated derivative,
11i, showed slightly more potent activity than did 11b,
while the ring-enlarged derivative, 11l, was less potent.
The dibenzylamino derivative, 11k,25 showed the most
potent inhibitory activity among our compounds, and
its IC50 was 0.84 lM, so that it is 11 times more potent
than 8d.
Next, structural modification of 8a was performed.
First, the effect of aromatic methyl substituents, that
is, 8a–d, was analyzed (Scheme 1). As shown in Table
1, 8b and 8d showed more potent inhibitory activity
(56% and 57%, respectively) than 8a, indicating that
methyl groups on the DPP skeleton are not required.
Therefore, further optimization of the structure was per-
formed based on 8d, and compounds 10a–g were pre-
pared (Scheme 2).
Next, the mode of inhibition of 11k was analyzed by
application of the Hanes–Woolf plot (Table 4). The
plot indicated that 11k inhibits 5aR-1 in a competitive
manner (the two dose–response lines were nearly par-
allel), as in the case of finasteride (1).26 This result
Scheme 2. Reagent and conditions: (a) phenol, methanesulfonic acid, 2–72 h, 31–98%.
Table 2. SAR of DPX skeleton analogs
Inhibition (%) at 10 lM
16
56
27
16
5
46
25
Scheme 3. Reagent and conditions: (a) 4-nitrophenylchloroformate, DMAP, DIPEA, THF, 30 min, 94%; (b) NHR2, DMF, 1 h, 77–97%.

S. Hosoda, Y. Hashimoto / Bioorg. Med. Chem. Lett. 17 (2007) 5414–5418
Table 3. SAR of carbamoyl derivatives
5417
Acknowledgments
The work described in this paper was partially sup-
ported by Grants-in-Aid for Scientific Research from
The Ministry of Education, Culture, Sports, Science
and Technology, Japan, and the Japan Society for the
Promotion of Science.
Compound –NR2
Inhibition (%) Inhibition (%) IC50
at 10 lM
at 1 lM
(lM)
References and notes
11a
8d
–NMe2
–NEt2
29
65
77
72
9.2
2.9
4.0
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Without inhibitor
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Vmax (nM/h)
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2300
13.4
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suggests that 11k is recognized by 5aR-1 as a sub-
strate mimic as expected; that is, the DPP skeleton
can act as a steroid skeleton substitute not only for
NR ligands, but also for enzymes which recognize ste-
roidal structures.
In summary, we developed novel 5aR-1 inhibitors
with a DPP skeleton. Compound 11k with a dib-
enzylamino group possessed the most potent inhibi-
tory activity among our derivatives. This is the first
example of a compound in which the DPP skeleton
can replace a steroid skeleton for target molecules
other than NRs, to our knowledge. Further structural
development of 11k and a search for new candidates
mimicking other biologically active steroids are in
progress.
22. Unpublished data; 3-(4-methoxyphenyl)-3-(4-(3-chlor-
ophenyl)phenyAl)pentane (6): 1H NMR (500 MHz,
˚
CDCl3/d): 7.56 (t, J = 2.1 Hz, 1H), 7.46–7.43 (m, 3H), 7.34
(t, J = 7.7 Hz, 1H), 7.28–7.23 (m, 3H), 7.11 (d, J = 9.0 Hz,
2H), 6.81 (d, J = 9.0 Hz, 2H), 3.79 (s, 3H), 2.11 (q,
J = 7.3 Hz, 4H), 0.65 (t, J = 7.3 Hz, 6H). HRMS (FAB,
M+) calcd for C24H25ClO: 364.1594; found: 364.1587.
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Prod. Rep. 1998, 495.

5418
S. Hosoda, Y. Hashimoto / Bioorg. Med. Chem. Lett. 17 (2007) 5414–5418
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Chem. 2002, 10, 437.
25. 4-(3-(4-(N-Methylacetamido)phenyl)pentan-3-yl)phenyl
J = 9.0 Hz, 2H), 4.56 (s, 2H), 4.53 (s, 2H), 3.25 (s, 3H),
2.10 (q, J = 7.3 Hz, 4H), 1.86 (s, 3H), 0.63 (t, J = 7.3 Hz,
6H); HRMS (FAB, M+H+) calcd for C35H39N2O3:
535.2961; found: 535.2964.
1
dibenzylcarbamate (11k): H NMR (500 MHz, CDCl3/d):
7.37–7.29 (m, 10H), 7.20 (d, J = 8.6 Hz, 2H), 7.17 (d,
J = 9.0 Hz, 2H), 7.06 (d, J = 8.6 Hz, 2H), 7.05 (d,
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