Bioorganic & Medicinal Chemistry Letters
Synthesis and acrosin inhibitory activities of substituted ethyl
5-(4-aminophenyl)-1H-pyrazole-3-carboxylate derivatives
Jingjing Qi a, Ju Zhu a, Xuefei Liu a, Lili Ding a, Canhui Zheng a, Guangqian Han b, Jiaguo Lv a,
,
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Youjun Zhou a,
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a Department of Medicinal Chemistry, School of Pharmacy, Second Military Medical University, Shanghai 200433, PR China
b Department of Pharmacognosy, School of Food Science, Fujian Agriculture and Forestry University, Fujian 350002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel ethyl 5-(4-aminophenyl)-1H-pyrazole-3-carboxylate derivatives were designed and
synthesized and their in vitro acrosin inhibitory activities were evaluated. Most of the compounds exhib-
ited acrosin inhibitory activities. Among them, three compounds (5l, 5n, and 5v) were more potent than
that of the control TLCK. These provide a new structural type for the development of novel contraceptive
acrosin inhibitory agents.
Received 8 March 2011
Revised 11 July 2011
Accepted 28 July 2011
Available online 3 August 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Acrosin inhibitory agents
Synthesis
Ethyl 5-(4-aminophenyl)-1H-pyrazole-3-
carboxylate
The problems of contraception are shared between men and
women. Currently, modern contraceptive methods have protected
millions of couples worldwide from unwanted pregnancy and al-
lowed them to take control over their reproduction. However,
forms of oral contraceptive pill. These can lead to serious side ef-
fects, such as most of these contraceptive methods are only avail-
able for women, especially the various breakthrough menstrual
bleeding, nausea, mood swings, headaches, and an increased risk
of rectal cancer.1–4 Male contraception is largely limited to con-
doms and vasectomy. It is clear that there is a need for new contra-
ceptive agents and methods which are easier to use with fewer
side effects to place the burden of contraception more equitably
between men and women.
Sperm acrosin is the major trypsin-like protease present in the
acrosome of all mammalian spermatozoa and plays a critical role in
fertilization.5 Acrosin is a sperm-specific enzyme, possibly in-
volved in the acrosome reaction, which functions in lysis of the
zona pellucida and in facilitating penetration of the sperm through
the innermost glycoprotein layers of the oocyte.6 Insufficient levels
of acrosin are associated with human infertility and inhibition of
acrosin activity by protease inhibitors has been shown to reduce
the success of fertilization.7 Thus, it is a potential target for the de-
sign and development of novel male contraceptive agents. Since
the function of acrosin was first reported, there has been much
research on acrosin inhibitors as potential contraceptives. A num-
ber of small molecules acting as acrosin inhibitors, such as TLCK,
AGB, DV-1006, and substituted isoxazolecarbaldehydes have been
reported (Fig. 1).8–10
Our group has focused on a search for novel acrosin inhibitors
for several years. In a previous study, our group constructed a
homologous three-dimensional model of human acrosin based on
the crystal structures of ram and boar form and the active site of
human acrosin was analyzed using the multiple copy simultaneous
search (MCSS) method.11 Based on these studies, a potent acrosin
inhibitory agent KF950 was designed and synthesized. This has
been the subject of preclinical study.12 Here, we report the synthe-
sis and acrosin inhibitory activities in vitro of novel ethyl 5-(4-ami-
nophenyl)-1H-pyrazole-3-carboxylate compounds.(Fig. 2; Table 1).
The chemical synthesis of ethyl 5-(4-aminophenyl)-1H-
pyrazole-3-carboxylate derivatives is outlined in Scheme 1. The 1-
(4-nitrophenyl)ethanone was oxalylated by diethyl oxalate in the
presence of sodium ethanol, affording b-diketoester. The b-diketo-
ester and hydrazine in refluxing ethanol yielded 5-(4-nitro-
phenyl)-1H-pyrazole-3-carboxylate (3). Then the reduction of (3)
to the key intermediate ethyl 5-(4-aminophenyl)-1H-pyrazole-3-
carboxylate (4). The target compounds 5a–5v were synthesized by
(4) with different acyl chlorides or anhydrides in the presence of tri-
ethylamine. The structures of these were determined by 1H NMRand
high resolution mass spectrum.
All the synthesized compounds were assessed for acrosin inhib-
itory activity using the method of Kennedy et al.13 The activities of
all the title compounds are listed in Table 1, in which TLCK was used
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Corresponding author. Tel.: +86 021 81871234.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
Qi, Jingjing
