Benzimidazole derivatives as novel nonpeptide luteinizing hormone-releasing hormone (LHRH) antagonists. Part 1: Benzimidazole-5-sulfonamides

Article abstract of DOI:10.1016/j.bmcl.2004.10.089

A new class of benzimidazole-5-sulfonamides has been identified as nonpeptide luteinizing hormone-releasing hormone (LHRH) antagonists. Initial structure-activity relationships are presented resulting in compounds 19 and 28 with submicromolar dual functio

Full text of DOI:10.1016/j.bmcl.2004.10.089

Bioorganic & Medicinal Chemistry Letters 15 (2005) 799–803
Benzimidazole derivatives as novel nonpeptide luteinizing
hormone-releasing hormone (LHRH) antagonists. Part 1:
Benzimidazole-5-sulfonamides
Kentaro Hashimoto,a,* Miyuki Tatsuta,a Mikayo Kataoka,a Kayo Yasoshima,a
Yuka Shogase,a Makoto Shimazaki,a Takeshi Yura,a Yingfu Li,a Noriyuki Yamamoto,b
Jang B. 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 3 September 2004; revised 28 October 2004; accepted 30 October 2004
Available online 21 November 2004
Abstract—A new class of benzimidazole-5-sulfonamides has been identified as nonpeptide luteinizing hormone-releasing hormone
(LHRH) antagonists. Initial structure–activity relationships are presented resulting in compounds 19 and 28 with submicromolar
dual functional activity on human and rat receptors.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
effective oral treatments of dysfunctional sex steroid
production. A plethora of nonpeptidic LHRH antago-
nists has been described to date.6 However most of them
are primate specific and lack potency on the rodent
receptor. This primate specificity is prohibitive for investi-
gating these compounds preclinically, for instance in
rodent disease models or toxicology studies. After ran-
dom screening of approximately one million compounds
we have identified 1-benzyl-2-ethylsulfanyl-1H-benzimi-
dazole-5-sulfonamide 1 as a functional LHRH antago-
nist with weak but dual activity on rat and human
receptors (Fig. 1).
Luteinizing hormone-releasing hormone (LHRH) is a
decapeptide hormone secreted in pulses from hypothal-
amus.1 Binding of LHRH to its receptor triggers the re-
lease of luteinizing hormone (LH) and follicular
stimulating hormone (FSH), which both regulate the
gonadal production of sex steroids. Dysfunctional sex
steroid production can result in disease states such as
benign and malign prostate growth, breast cancer and
endometriosis.2,3
The treatment with peptidic LHRH agonists is known
to desensitize the receptor and results in suppressing ser-
um testosterone to the castration level.4 This treatment,
albeit efficient is associated with adverse effects such as
hot flush, flare effects and impotence. Peptidic LHRH
receptor antagonists have shown clinical efficacy with
less side effects.5 As peptides however, these agents are
not amenable to oral administration. Nonpeptidic
LHRH antagonists would therefore be expected to be
In this report, we will describe the SAR and optimiza-
tion of 1 towards submicromolar rat and human LHRH
antagonists.
N
H
N
S
N
S
Keywords: LHRH antagonist; Small molecule.
O
O O
*
Corresponding author at present address: Bayer HealthCare AG.,
Pharma Research Center, D-42096 Wuppertal, FRG, Germany.
Tel.: +49 (0)202 36 8131; fax: +49 (0)202 36 4624; e-mail:
kentaro.hashimoto@bayerhealthcare.com
IC50=3.5 µM(rat-lhrh, Ca2+
3.4 µM (human-lhrh, Ca2+
)
)
Figure 1. Functional activity of lead compound 1.
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.10.089

800
K. Hashimoto et al. / Bioorg. Med. Chem. Lett. 15 (2005) 799–803
H
H
N
Z
Z
Cl
N
b
c, d or e
H
N
a
H
N
H
N
Y
Y
Y
Y
S
NO2
S
NO2
S
NH2
O
O
O
O
O
O
O
S
3
2
4
Z
Z
N
N
N
F
N
N
f
g or h
H
N
X
H
N
Cl
Y
H
X
N
H
N
S
S
R1
O
O
O
O
O
5
6
i or j
12 : X=O, R1= CH3
CH
N
O
22 : X=O, R1=
2
F
11 : R1= CH3
CH
N
N
H
N
S
N
H
24 : R1=
R1
CH
O
23 : X=NH, R1=
N
2
S
2
O
O
Scheme 1. Reagents and conditions: (a) benzylamine, triethylamine, CH3CN, 65°C, 97%; (b) H2, 10% Pd/C, THF, rt, 99%; (c) X = S, CS2, DIPEA,
EtOH, 50°C, 78%; (d) X = O, CDI, THF, rt, 43%; (e) (EtO)4C, HOAc, CHCl3, 38%; (f) POCl3, 100°C, 35%; (g) 4-(2-hydroxyethyl)-morpholine,
t-BuOK, THF–DMF, 110°C, 41%; (h) N-(2-aminoethyl)morpholine, neat, 90°C, 47%; (i) EtI, triethylamine, THF, rt, 74%; (j) N-benzylethanol-
amine, PPh3, di-t-butylazodicarboxylate, CH2Cl2, rt, 25%.
2. Chemistry
of functional tolerance in this structural area. Also, the
incorporation of a hydroxyl group or a carboxylic ester
group was tolerated in this position (14, 15). In an addi-
tional experiment, we confirmed the activity of 13 by
determining its binding constant to the human LHRH
receptor (IC50 = 0.22 lM).13
The 1-alkylated benzimidazole-5-sulfonamide analogues
were prepared according to the procedure outlined in
Scheme 1. Dianilines 4 were prepared as common inter-
mediates by standard methods from sulfonamide 2.7 The
resulting dianilines 4 were then treated with carbondisul-
fide, followed by addition of EtI or MeI to form ethyl-
(or methyl)-sulfanyl-1H-benzimidazoles 7–11, 13, 16
and 21.8 The oxy-linked analogues 12, 17–18 and 20
were obtained from dianilines 4 on heating with tetra-
ethoxymethane in HOAc.9
The structure–activity relationship around the benzimid-
azole N-alkyl fragment was much more conservative
and even minor variations led to complete loss of activ-
ity (16–18).
Most known LHRH antagonists display a flexible side
chain, typically associated with a secondary or tertiary
amine.6 Hoping to improve the potency of our lead,
we introduced an ethyl morpholino group as a basic side
chain at three different positions (Table 2). In accord
with trends observed earlier, basic functionality was tol-
erated best in 2-position, which led to the discovery of
19. Interestingly, the presence of a S-linker was crucial
in the case of 19, the corresponding O- or N-linker re-
sulted in loss of potency (22, 23). The morpholino frag-
ment could be replaced by other basic moieties such as
benzylamines or pyridine containing compounds (24–
28). A 3-picolyl group appeared to be optimal, furnish-
ing 28, which is 28-fold more potent than the lead
compound 1.
Thiourea 5 (X = S) was subjected to a Mitsunobu reac-
tion with various amino alcohols in order to afford 19,
and 24–28.10 We did not observe the corresponding N-
alkylation products. Alternatively, 4 could be converted
to the corresponding urea (5: X = O) followed by treat-
ment with phosphoryl chloride11 to yield the corre-
sponding 2-chloro-1H-benzoimidazole 6.
Intermediate 6 could be easily converted with primary
alcohols and amines to prepare the corresponding
O,N-linked benzimidazoles 22 and 23 under basic
conditions.
3. Results and discussion
In summary, the potency of our initial lead 1 was im-
proved by changing the aromatic substitution pattern
in the sulfonamide moiety as well as through incorporat-
ing a basic functionality at the 2-position of the benzimid-
azole core. These SAR investigations led to two
optimized compounds, 19 and 28, which show improved
potency by 1.5 orders of magnitude. Of note, this opti-
mization was possible on both human and rat receptors.
The compounds listed in Tables 1–3 have been evaluated
as functional antagonists for both rat and human
LHRH receptors.12 All inhibition constants (IC50) are
means of at least two experiments each run in triplicates.
The substitution pattern of the sulfonamide phenyl ring
had a strong effect on potency with electron withdraw-
ing substituents in para-position providing first sub-
micromolar examples (10, 11). The corresponding
ethyl oxy-ether 12 and the methyl sulfide 13 both
showed potencies similar to 11 indicating a high degree
However, LHRH exhibits picomolar affinities to its
receptor and reaches high peak concentrations after its

K. Hashimoto et al. / Bioorg. Med. Chem. Lett. 15 (2005) 799–803
Table 1. Functional activity of compounds 7–18
801
R2
N
N
X
H
N
R1
S
R3
O
O
7-18
Compd
XR1
R2
R3
IC50 (lM)
r-LHRH
4.0
h-LHRH
4.8
O
7
S–Et
8
S–Et
0.94
1.2
1.1
1.1
O
9
S–Et
NO2
10
11
12
13
14
15
16
17
18
S–Et
0.33
0.20
0.47
0.21
0.60
0.81
>10
1.9
0.28
0.25
0.30
0.22
0.27
0.49
>10
0.88
1.4
Cl
F
F
F
F
F
F
F
F
S–Et
O–Et
S–Me
S(CH2)2OH
SCH2CO2Et
S–Et
Cl
O–Et
O–Et
2.0
S
Table 2. Introduction of basic side chains into structure 11. Functional activity of compounds 19–21
R2
N
X
H
N
N
S
R1
R3
O
O
Compd
X-R1
R2
R3
IC50 (lM)
r-LHRH
0.20
h-LHRH
0.25
11
19
–SEt
F
F
S
N
0.17
7.2
0.16
2.1
O
N
20
21
–OEt
–SEt
O
F
N
>10
>10
O

802
K. Hashimoto et al. / Bioorg. Med. Chem. Lett. 15 (2005) 799–803
Table 3. Functional activity of compounds 22–28
1
3
F
N
N
H
N
X
S
R1
O
O
Compd
X
R1
IC50 (lM)
r-LHRH
3.2
h-LHRH
5.8
N
N
22
23
O
O
O
NH
>10
0.53
0.96
0.24
0.28
0.14
>10
0.67
0.82
0.32
0.23
0.12
N
H
24
25
26
27
28
S
S
S
S
S
N
N
N
N
release into the hypothalamus.14 Therefore, despite the
respectable potency of our compounds, we felt that fur-
ther optimization towards at least single digit nanomo-
lar compounds would be necessary for investigations
of our lead structure in vivo.
Young, J. R.; Ujjainwalla, F.; Toupence, R. B.; Parkh,
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.
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J. Med. Chem. 2001, 44, 917.
7. Wu, Z.; Rea, P.; Wickham, G. Tetrahedron Lett. 2000, 41,
9871.
References and notes
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10. Typical procedure to prepare 2-substituted benzimidazole
(synthesis of compound 28); To a stirred solution of
thiourea 5 (50.0mg, 0.120mmol), 3-(2-hydroxyethyl)pyri-
dine (14.4mg, 0.120mmol), and polymer supported PPh3
(1.6mmol/g, 146mg, 0.230mmol) in CH2Cl2 was added di-
tert-butylazodicarboxylate (53.9mg, 0.230mmol). The
resulting suspension turned to be a clear solution in 5min.
The solution was stirred at room temperature for 2h. After
filtering off the resin, the filtrate was concentrated in vacuo.
The crude residue was purified through preparative thin
layer chromatography (CH2Cl2/MeOH = 20/1) to give
desired 1-benzyl-2-(2-pyridin-3-yl-ethylsulfanyl)-1H-benz-
imidazole-5-(4-fluorobenzyl)sulfonamide 28 (19.5mg, 31%
yield) as waxy material. 1H NMR (300MHz, CDCl3): d
3.14–3.19 (2H, t, J = 7.4Hz), 3.64–3.69 (2H, t, J = 7.4Hz),
4.10–4.12 (2H, d, J = 6.2Hz), 4.87 (1H, br s), 5.29 (2H, s),
6.88–6.93 (2H, t, J = 8.7Hz), 7.13–7.38 (9H, m), 7.60–7.68
(2H, m), 8.21 (1H, s), 8.46–8.51 (2H, m).
11. James, A. T.; Turner, E. E. J. Chem. Soc. 1950, 1515.
12. Intracellular Ca mobilization data were obtained using
recombinant CHO cells transfected with human and rat
LHRH receptor cDNA. The cells were preincubated with
a variable concentration of test compounds for 20min at

K. Hashimoto et al. / Bioorg. Med. Chem. Lett. 15 (2005) 799–803
803
25°C. Fluorescence changes indicating mobilization of
cytoplasmic calcium (Flu-3 AM, Molecular Probes) were
measured on a FDSS-3000 machine (Hamamatsu pho-
tonics) after the stimulation with 10nM LHRH for human
receptor expressing cells and 1nM LHRH for rat receptor
expressing cells. The inhibitory effect of the compounds
was calculated by comparing the Integral ratio (ratio = ac-
tual fluorescence/initial fluorescence).
CHO cells12 were incubated with 150pM of [125I]-D-
Trp6-LHRH (Pharmacia) in the presence of various
concentration of compounds in assay buffer. The total
binding was defined as that measured in the absence of a
competing agent. Nonspecific binding was determined in
the presence of 10lM D-Trp6-LHRH.
14. Cho, N.; Harada, M.; Imaeda, T.; Imada, T.; Matsumoto,
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13. The receptor binding assay was performed according to
Ref. 14. Briefly, membrane fractions from recombinant