Benzimidazoles as non-peptide luteinizing hormone-releasing hormone (LHRH) antagonists. Part 3: Discovery of 1-(1H-benzimidazol-5-yl)-3-tert-butylurea derivatives

Article abstract of DOI:10.1016/j.bmcl.2005.03.030

1-(1H-Benzimidazol-5-yl)-3-tert-butylurea derivatives have been identified as a novel class of non-peptide luteinizing hormone-releasing hormone (LHRH) antagonists. Herein, we disclose the synthesis and structure-activity relationships (SAR) of this class

Full text of DOI:10.1016/j.bmcl.2005.03.030

Bioorganic & MedicinalChemistry Letters 15 (2005) 2265–2269
Benzimidazoles as non-peptide luteinizing
hormone-releasing hormone (LHRH) antagonists. Part 3:
Discovery of1-(1 H-benzimidazol-5-yl)-3-tert-butylurea derivatives
Miyuki Tatsuta,a,* Mikayo Kataoka,a Kayo Yasoshima,a Sachiko Sakakibara,a
Yuka Shogase,a Makoto Shimazaki,a Takeshi Yura,a Yingfu Li,a Noriyuki Yamamoto,b
Jang Guptab and Klaus Urbahnsa
aDepartment of Chemistry, Research Center Kyoto, Bayer Yakuhin, Ltd, Kizu, Soraku, Kyoto 619-0216, Japan
bDepartment of Biology, Research Center Kyoto, Bayer Yakuhin, Ltd, Kizu, Soraku, Kyoto 619-0216, Japan
Received 1 February 2005; accepted 3 March 2005
Abstract—1-(1H-Benzimidazol-5-yl)-3-tert-butylurea derivatives have been identified as a novel class of non-peptide luteinizing hor-
mone-releasing hormone (LHRH) antagonists. Herein, we disclose the synthesis and structure–activity relationships (SAR) of this
class resulting in the identification of compound 12c, with dualfunctionalactivity on human and rat receptors (rat LHRH:
IC50 = 120 nM; human LHRH: IC50 = 18 nM). These SAR studies suggest that 1-(1H-benzimidazol-5-yl)-3-tert-butylurea is a
new pharmacophore for small molecule LHRH antagonists.
Ó 2005 Elsevier Ltd. All rights reserved.
1. Introduction
with compound 1, which was identified by high through-
put screening of our compound library, a series of benz-
imidazoles was synthesized and evaluated as LHRH
antagonists (Fig. 1). In this report, we describe the syn-
thesis and SAR of benzimidazoles. Whereas the molecu-
lar core is identical to those in the earlier series, the
substitution pattern demonstrates unprecedented SAR,
probably suggesting an alternative binding mode.
Luteinizing hormone-releasing hormone (LHRH)
antagonists have been investigated by many groups as
a potentialnew treatment for hormone-dependent dis-
eases, such as endometriosis, breast cancer, and prostate
cancer.1,2 Clinical use of peptidic LHRH agonists is
hampered by desensitization of the receptor resulting
in suppression of serum testosterone to castration levels.
This treatment is accompanied with undesirable side ef-
fects such as the concomitant ÔflareÕ effect. Clinical evi-
dence suggests that peptidic LHRH antagonists
directly lower steroid hormone levels and alleviate dis-
ease symptoms without ÔflareÕ effects.2,3 In addition,
small molecule non-peptidic LHRH antagonists would
possess advantages over existing peptidyltherapeutics
due to their potentialfor oraladministration.
2. Chemistry
The synthesis of various benzimidazoles is outlined in
Scheme 1.5 Common intermediate anilines 5 were
prepared from 2 by standard substitution and reduction
methods. Anilines 5 were treated with carbon disulfide
In previous publications, our group described benzimid-
azoles as LHRH antagonists.4 In order to reduce attri-
tion at later stages of development, additional efforts
have been devoted toward searching for new pharmaco-
phores of small molecule LHRH antagonists. Starting
N
O
S
N
N
H
1
IC = > 10
(rat-LHRH, Ca2+)
µΜ
50
6.5 µΜ (human-LHRH, Ca2+)
*
Figure 1. Biological activity of lead compound 1.
Corresponding author. E-mail: miyuki.tatsuta@pfizer.com
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.03.030

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M. Tatsuta et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2265–2269
R2
NH
R2
NH
F
F
NO2
O
a
b
c
O
O
R1
N
H
NH2
H2N
NO2
R1
N
H
R1
N
H
NO2
2
3: R1= -cyclopropyl
8: R1= -NH-tert-butyl
13: R1= -O-tert-butyl
5: R1= -cyclopropyl
10: R1= -NH-tert-butyl
15: R1= -O-tert-butyl
4: R1= -cyclopropyl
9: R1= -NH-tert-butyl
14: R1= -O-tert-butyl
R2
N
R2
N
R2
N
d
e
O
O
O
S
S
S
R1
N
R3
N
H
X
N
H
R1
N
N
R3
R1
N
H
H
6: R1= -cyclopropyl
11: R1= -NH-tert-butyl
16: R1= -O-tert-butyl
7: R1= -cyclopropyl
12: R1= -NH-tert-butyl
17: R1= -O-tert-butyl
f, g
18: X = C
19: X = N
Scheme 1. Reagents and conditions: (a) cyclopropanecarbonyl chloride, Et3N, CH2Cl2, rt, or 2-isocyanato-2-methylpropane, Et3N, CH2Cl2, rt, or
di-tert-butylcarbonate, Et 3N, CH3CN, rt; (b) R2NH2, Et3N, CH3CN, 50 °C; (c) SnCl2–2H2O, EtOH, DMF, 50 °C; (d) CS2, DIPEA, EtOH, 60 °C;
(e) R3Br, DIPEA, THF, rt, or R3OH, DEAD, Ph3P, THF, rt; (f) 4 N HCl–dioxane, rt; (g) R1CH2COOH, Et3N, CH2Cl2, rt, or R1NCO, Et3N,
CH2Cl2, rt.
to give thioureas 6, which were treated with benzylbro-
mide under basic condition or subjected to a Mitsunobu
reaction with various alcohols to afford 7. A similar syn-
thetic strategy was applied for the synthesis of 12 and
17. Compound 2 was reacted with 2-isocyanato-2-meth-
ylpropane or di-tert-butylcarbonate instead of acyl
chloride. After four steps, 12 and 17 were obtained.
Deprotection of 17 was achieved under acidic condition
to give the amine as its HClsatl. These were converted
to amides 18 or urea 19 under standard conditions.
Compounds in Table 4 were prepared from a common
intermediate 23, which was synthesized via 20. The syn-
thesis of compound 26 is outlined in Scheme 2. Aniline
21 was prepared from 20 by standard methods using
substitution and reduction reactions.5 Compound 21
was treated with carbon disulfide to prepare the corre-
sponding thiourea, which was converted to 22. Com-
pound 22 was treated with 2-methoxy-5-nitrobenzyl
bromide under basic condition to give 23, which gave
carboxylic acid 24 after hydrolysis. Compound 24 was
immobilized on solid support to give a TFP polymer-
bound ester 25, which was treated with pyrrolidine to
furnish crude 26.6 Excess amine and carboxylic acid
were removed with methylisocyanate polystyrene (PS-
NCO) and 1,5,7-triazabicyclo[4,4,0]dec-5-ene polysty-
rene (PS-TBD), respectively, to give pure material 26.7
Compounds 26a–m were synthesized similarly.
3. Results and discussion
The synthesized compounds were evaluated as func-
tionalantagonists of both rat and human receptors
according to methods in the literature (Tables 1–4).4
First, substitution at the 2-position of the benzimidazole
core was explored (Table 1). The substitution pattern of
the phenylring had a strong effect on potency with
O
O
O
O
O
O
O
O
e
a, b
c, d
Cl
NH
N
O
NO2
N
N
S
O
O2N
NO2
S
H2N
NH2
N
H
N
H
N
H
N
H
N
H
21
22
20
23
MeO
F
Pol
F
HO
O
N
O
F
O
O
NO2
N
N
f
g
O
F
O
h
S
NO2
NO2
N
N
N
N
O
N
N
H
S
S
H
N
H
N
H
N
N
H
H
MeO
24
25
MeO
26
MeO
Scheme 2. Reagents and conditions: (a) n-propylamine, CH2Cl2, rt, 89%; (b) Pd/C, H2, AcOEt, rt, quant.; (c) CS2, DIPEA, EtOH, 60 °C, quant.; (d)
2-isocyanato-2-methylpropane, Et3N, THF, 40 °C, 98%; (e) 2-(bromomethyl)-1-methoxy-4-nitrobenzene, DIPEA, rt, 72%; (f) 1 N NaOH–H2O,
MeOH, 65 °C, 91%; (g) PS-tetrafluorophenol, N,N0-diisopropylcarbodiimide, DMAP, NMP; (h) pyrrolidine, DMF, rt; then PS-NCO, PS-MTBD, rt,
55% (two steps).

M. Tatsuta et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2265–2269
2267
Table 1. Modification of the 2-substituted benzimidazole
Table 2. Modification of the 5-substituted benzimidazole
1
NO2
N
N
O
O
S
S
2
N
N
R
N
H
R
N
H
MeO
Compd
R
IC50 (lM)
Compd
R
IC50 (lM)
h-LHRH
r-LHRH
h-LHRH
r-LHRH
0.71
7a
7b
>10
3.2
17a
18a
0.88
1.5
O
0.63
1.5
>10
>10
>10
2.1
MeO
18b
18c
18d
19a
19b
19c
19d
0.25
0.18
0.18
0.062
0.6
7c
7d
6.3
>10
0.11
0.062
0.28
>10
1.6
Cl
COOMe
COMe
CN
0.98
N
H
MeO
MeO
MeO
MeO
MeO
N
H
7e
7f
>10
>10
>10
>8.2
0.26
0.57
0.16
0.28
N
3.3
H
1.9
N
H
Cl
Table 3. Modification of the N1-substituted benzimidazole
7g
7h
R
N
NO2
O
S
NO2
N
N
H
N
H
MeO
Compd
R
IC50 (lM)
r-LHRH
0.86
h-LHRH
0.079
electron-donating substituents in the ortho-position and
electron-withdrawing substituents in the meta-position,
giving submicromolar antagonists of the human LHRH
receptor. These compounds (7a–h), however, were inac-
tive at the rat LHRH receptor, prohibiting rodent in
vivo experiments.
12a
12b
0.17
0.042
12c
12d
12e
12f
0.12
0.33
0.88
0.28
0.018
0.023
0.21
We also investigated the SAR at the 5-position of the
benzimidazole core (Table 2). Replacement of the cyclo-
propylmoiety of 7h with cyclobutyl led to loss of activ-
ity for the human receptor (see compound 18a). It was
interesting that acyclic alkyl substituted analogs 18b–d
were found to have good potency. Furthermore, we
were delighted to see that 18d was potent against both
rat and human receptors. This result prompted us to
investigate the SAR of the acetamide further. Replace-
ment of the methylene in the amide portion of 18d with
a heteroatom gave 17a and 19a. Whil etert-butylcarba-
mate 17a was less potent, the corresponding urea 19a
was the first example of a double-digit nanomolar antag-
onist of both rat and human receptors in this series. The
SAR observed among 17a, 18d, and 19a clearly indicates
the importance of two-hydrogen-bond donors for
OMe
0.057
12g
12h
12i
12j
0.16
0.3
0.028
0.36
0.67
0.15
0.043
0.033
N
N
12k
12l
0.24
>2.6
0.047
0.35
N

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M. Tatsuta et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2265–2269
Table 4. Modification of the 7-substituted benzimidazole
potency. Within the series, however, the n-propylanalog
12c was the most potent.
R
NO2
N
N
We also explored effects on introducing an additional
substituent in the 7-position of the benzimidazole core
(Table 4). We were delighted to find that the pyrrolidine
amide analog 26 was still potent, despite its considerable
structuralmodification. Repal cement of the pyrroildine
moiety of 26 with dimethylamine maintained potency
(see compound 26a). Removalof one methylmoiety in
26a even improved activity (see compound 26b). The
SAR observed among 26, 26a, and 26b clearly indicates
the importance of an amide NH for optimalinteraction
with the LHRH receptor. This result prompted us to
investigate the SAR of the amide further. Oxygen deriva-
tives 23 as well as 24 have good potency at the human
receptor, but are less potent at the rat receptor. Within
this series, 26b was the another example of a double-di-
git nanomolar antagonist on both rat and human recep-
tors. Therefore, we focused on the modification of mono
alkyl amides. tert-Butylamide anaol g 26c showed a de-
crease in potency. Interestingly, the alkyl groups could
be replaced with benzyl with only a slight loss in potency
(see compound 26d). Most known LHRH antagonists
contain a basic moiety.8 This inspired us to introduce
severalbasic functionailties into our LHRH antagonists
(see compounds 26e–m). Indeed, the incorporation of
the pyridine ring (26e–j) improved potency compared
to 26d. The introduction of tertiary or primary amines
(26k–m) resulted in good activity for the rat LHRH
receptor, but reduced potency against the human
receptor.
O
S
N
H
N
H
MeO
Compd
R
IC50 (lM)
r-LHRH
h-LHRH
O
23
24
0.28
0.037
O
O
0.51
0.021
HO
O
26
0.140
0.200
0.610
0.270
N
O
26a
N
O
26b
26c
0.023
0.49
0.041
0.41
N
H
O
N
H
O
26d
26e
26f
0.13
0.12
N
H
O
N
N
0.035
0.054
0.061
0.069
N
H
O
O
N
H
26g
26h
26i
26j
26k
26l
0.051
0.045
0.11
0.031
0.13
0.16
0.027
0.17
0.19
Of all analogs, the n-propylcompound 12c was the most
potent functionalantagonist on the human receptor
(IC50 = 0.018 lM).9 We confirmed the activity of 12c
by determining its binding constant to the human
LHRH receptor (IC50 = 0.073 lM).4
N
H
N
O
O
N
N
N
H
N
H
4. Conclusion
O
0.056
0.019
0.021
N
N
H
We have identified a novelseries of LHRH antagonists,
represented by the n-propylcompound 12c, with strong
potency against both rat and human LHRH receptors.
These SAR studies suggest that 1-(1H-benzimidazol-5-
yl)-3-tert-butylurea is a new pharmacophore for small
molecule LHRH antagonists.
N
O
N
H
N
O
N
H
O
26m
0.055
0.21
N
H
H2N
References and notes
1. Filicori, M.; Flamigni, C. Drugs 1998, 35, 63.
2. (a) Huirne, J. A. F.; Lambalk, C. B. Lancet 2001, 358, 1793;
(b) Goulet, M. T. In Annual Reports in Medicinal Chem-
istry; Bristol, J. A., Ed.; Academic: New York, 1995; Vol.
30, p 169.
3. Blithe, L. D. Trends Endocrinol. Metab. 2001, 12, 238.
4. (a) Hashimoto, K.; Tatsuta, M.; Urbahns, K. Bioorg. Med.
Chem. Lett. 2005, 15, 799; (b) Li, Y.; Kataoka, M.;
Hashimoto, K. Bioorg. Med. Chem. Lett. 2005, 15, 805.
5. Lee, J.; Gauthier, D.; Rivero, R. A. Tetrahedron Lett. 1998,
39, 201.
optimalinteraction with the LHRH receptor. Further
modification of the tert-butylmoiety in 19a did not yield
more potent analogs (see compounds 19b–d). Therefore,
compound 19a was chosen for further investigations.
The SAR of the benzimidazole N-alkyl fragment was
less restrictive (Table 3). In general, small alkyl substi-
tuted compounds 12a–f showed good potency. With
the exception of analog 12l, replacement of the alkyl
groups with aromatic substituents (12g–k) maintained
6. Salvino, J. W. J. Comb. Chem. 2000, 2, 691.

M. Tatsuta et al. / Bioorg. Med. Chem. Lett. 15 (2005) 2265–2269
2269
7. Typicalprocedure for preparing compound 26; To a
mixture of resin-bound active ester 25 (76 mg, 0.050 mmol,
0.66 mmol/g) in DMF (0.5 mL) was added pyrrolidine
(0.0046 mL, 0.055 mmol) and the mixture was stirred
overnight. PS-NCO (13 mg, 0.0125 mmol, 1 mmol/g) and
PS-MTBD (5 mg, 0.0125 mmol, 2.6 mmol/g) were added to
the suspension, which was stirred for 6 h. The resin was
removed by filtration, and the filtrate was concentrated to
give 26 (3.9 mg, 55% yield) as a colorless solid. Compound
26: 1H NMR (500 MHz, DMSO-d6) d 0.74 (3H, t,
J = 7.3 Hz), 1.30 (9H, s), 1.46 (2H, sextet, J = 7.3 Hz),
1.79 (2H, quintet, J = 6.9 Hz), 1.90 (2H, quintet,
J = 6.9 Hz), 3.16 (2H, t, J = 6.9 Hz), 3.51 (2H, t,
J = 6.9 Hz), 3.92 (2H, t, J = 7.3 Hz), 3.97 (3H, s), 4.60
(2H, s), 5.94 (1H, s), 7.25 (1H, d, J = 9.1 Hz), 7.25 (1H, d,
J = 1.9 Hz), 7.51 (1H, d, J = 1.9 Hz), 8.20 (1H, dd, J = 2.8,
9.1 Hz), 8.26 (1H, s), 8.40 (1H, d, J = 2.8 Hz).
8. (a) Zhu, Y.-F.; Guo, Z.; Gross, T. D.; Gao, Y.; Connors, P.
J., Jr.; Struthers, R. S.; Xie, Q.; Tucci, F. C.; Reinhart, G.
J.; Wu, D.; Saunders, J.; Chen, C. J. Med. Chem. 2003, 46,
1769; (b) Sasaki, S.; Cho, N.; Nara, Y.; Harada, M.; Endo,
S.; Suzuki, N.; Furuya, S.; Fujino, M. J. Med. Chem. 2003,
46, 113; (c) Young, J. R.; Huang, S. X.; Walsh, T. F.;
Wyvratt, M. J., Jr.; Yang, Y. T.; Yudkovitz, J. B.; Cui, J.;
Mount, G. R.; Ren, R. N.; Wu, T.-J.; Shen, X.; Lyons, K.
A.; Mao, A.-H.; Carlin, J. R.; Karanam, B. V.; Vincent, S.
H.; Cheng, K.; Coulet, M. T. Bioorg. Med. Chem. Lett.
2002, 12, 827; (d) DeVita, R. J.; Walsh, T. F.; Young, J. R.;
Jiang, J.; Ujjainwalla, F.; Toupence, R. B.; Parikh, M.;
Huang, S. X.; Fair, J. A.; Goulet, M. T.; Wyvratt, M. J.;
Lo, J.-L.; Ren, N.; Yudkovitz, J. B.; Yang, Y. T.; Cheng,
K.; Cui, J.; Mount, G.; Rohrer, S. P.; Schaeffer, J. M.;
Rhodes, L.; Drisko, J. E.; McGowan, E.; MacIntyre, D. E.;
Vincent, S.; Carlin, J. R.; Cameron, J.; Smith, R. G. J.
Med. Chem. 2001, 44, 917.
9. Typicalprocedure for preparing compound 12c: To a
solution of 1-tert-butyl-3-(1-propyl-2-thioxo-2,3-dihydro-
1H-benzimidazol-5-yl)-urea (11: R1 = –NH-tert-butyl,
R2 = n-propyl) (18.0 mg, 0.06 mmol) in THF was added
2-(bromomethyl)-1-methoxy-4-nitrobenzene
(28.9 mg,
0.12 mmol) and N,N-diisopropylethylamine (0.021 mL,
0.12 mmol). The resulting mixture was stirred at room
temperature for 16 h. The solution was concentrated in
vacuo. The crude residue was purified through preparative
thin layer chromatography (AcOEt/Hex = 9/4) to give 12c
(21.0 mg, 76% yield) as a pale yellow solid. Compound 12c:
1H NMR (500 MHz, DMSO-d6) d 0.78 (3H, t, J = 7.3 Hz),
1.3 (9H, s), 1.65 (2H, sextet, J = 7.3 Hz), 3.97 (3H, s), 3.99
(2H, t, J = 7.3 Hz), 4.58 (2H, s), 5.88 (1H, s), 7.10 (1H, dd,
J = 1.6, 8.5 Hz), 7.24 (1H, d, J = 9.2 Hz), 7.31 (1H, d,
J = 8.5 Hz), 7.63 (1H, d, J = 1.6 Hz), 8.15 (1H, s), 8.19 (1H,
dd, J = 2.8, 9.2 Hz), 8.38 (1H, d, J = 2.8 Hz).