Synthesis and antiproliferative evaluation of N,N-disubstituted-N′- [1-aryl-1H-pyrazol-5-yl]-methnimidamides

Article abstract of DOI:10.1016/j.bmcl.2010.08.133

A series of N,N-disubstituted-N′-[1-aryl-1H-pyrazol-5-yl]- methnimidamides was synthesized by a newly developed microwave reaction and their antiproliferative activities were evaluated. Microwave irradiation of 5-amino-1,3-disubstituted pyrazoles with var

Full text of DOI:10.1016/j.bmcl.2010.08.133

Bioorganic & Medicinal Chemistry Letters 20 (2010) 6781–6784
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antiproliferative evaluation
of N,N-disubstituted-N0-[1-aryl-1H-pyrazol-5-yl]-methnimidamides
Kaung-Min Cheng a, Yu-Ying Huang a, Jiann-Jyh Huang b, Kimiyoshi Kaneko c, Masayuki Kimura c,
a,
Hiroyuki Takayama c, Shin-Hun Juang a, , Fung Fuh Wong
⇑
⇑
a Graduate Institute of Pharmaceutical Chemistry, China Medical University, No. 91 Hsueh-Shih Rd., Taichung 40402, Taiwan, ROC
b Development Center for Biotechnology, No. 101, Lane 169, Kangning St., Xizhi City, Taipei County 221, Taiwan, ROC
c Department of Medico Pharmaceutical Science, Nihon Pharmaceutical University, 10281, Komuro, Inamachi, Kita-Adachigun, Saitama, Japan
a r t i c l e i n f o
a b s t r a c t
A series of N,N-disubstituted-N0-[1-aryl-1H-pyrazol-5-yl]-methnimidamides was synthesized by a newly
developed microwave reaction and their antiproliferative activities were evaluated. Microwave irradia-
tion of 5-amino-1,3-disubstituted pyrazoles with various amide solvents in the presence of POCl3 pro-
vided the corresponding 2a–2k, 3a–3c, and 4a–4f in good to excellent yields. The obtained
methnimidamides were tested against NCI-H661, NPC-TW01, and Jurkat cancer cell lines and the results
indicated that compounds 2d and 2e were the most potent with IC50 values in low micromolar range.
Ó 2010 Elsevier Ltd. All rights reserved.
Article history:
Received 22 June 2010
Revised 30 July 2010
Accepted 26 August 2010
Available online 18 September 2010
Keywords:
Amidines
Pyrazoles
Antiproliferative activity
Microwave-assisted reaction
Formylation
Amidinyl groups are intensively studied since they contribute
to the activities of many biologically important compounds includ-
ing anticancer,1,2 anti-degenerative,3 anti-platelet,4 antimicrobial,5
antibacterial, antiprotozoal, anti-tumor drugs,6–8 serine protease
inhibitors,5 and nitric oxide synthase inhibitors.9 The introduction
extensively utilized precursors to construct the heterocyclic rings,
such as fused pyrazolo[3,4-b]pyridines, pyrazolo[3,4-b]pyridones,
and pyrazolo[3,4-d]pyrimidines.18 In this Letter, we reported an
efficient synthesis for the introduction of an amidinyl group into
the C-5 position of N-arylpyrazoles by use of commercially avail-
22
of an amidinyl group into
a
known biological molecule is
able amide solvents and POCl3 to provide the compound. The
consequently of interest in the field of medicinal chemistry and
demonstrates good results in several models. The grafting of the
amidinyl group is found to enhance the antibacterial activity of
penicillin,10–12 and improve the therapeutic window of anthracy-
clines.13 Except for acting as valuable pharmacophore, amidines
are also important building blocks for the preparation of various
heterocyclic compounds,14 protecting groups for primary amines,15
support linkers in solid phase synthesis,16 and auxiliaries in asym-
metric synthesis.17
Pyrazoles are among the important scaffolds possessing various
biological activities. The bioactivity of functionalized N-arylpyraz-
ole was extensively studied19–21 and the C-5 substituted pyrazoles
are also exploited in the design of pharmaceuticals and agrochem-
ical agents.20 N,N-Dimethyl-N0-[1-aryl-3-phenyl-1H-pyrazol-5-yl]-
methnimidamide derivatives are C-5 substituted N-arylpyrazoles
antiproliferative activities of the methnimidamide derivatives
were explored on cancer cells and the structure–activity relation-
ship was established.
Scheme 1 illustrates the amidination of 5-amino-1,3-disubsti-
tuted pyrazoles 1a–1k to the corresponding 1a–1k and the optimi-
zation of the reaction. A model procedure involved the treatment
of 5-amino-1,3-disubstituted pyrazoles 1a with a catalytic amount
of POCl3 (ꢀ1.2 equiv) in DMF at 30–40 °C with 100 W of micro-
wave energy within 10–15 min. After work-up and purified by col-
umn chromatography on silica gel, the corresponding amidination
product 2a was obtained in 94% yields (see Table 1). In addition to
H
O
X
X
NMe2
NH2
N
H
NMe2 (DMF)
POCl3, MW
CHO
N
N
N
N
⇑
Y
Y
Corresponding authors. Tel.: +886 4 2205 3366x5603; fax: +886 4 2207 8083
(F.F.W.).
1a-1k
2a-2k
E-mail addresses: wongfungfuh@yahoo.com.tw, ffwong@mail.cmu.edu.tw (F.F.
Wong).
Scheme 1.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.08.133

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K.-M. Cheng et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6781–6784
Table 1
To realize the effect of the substituent on the pyrazole ring for
the reaction, 5-amino-1-phenyl-3-substituted pyrazoles 1h–1k
containing the t-butyl, p-Me-Ph, p-Cl-Ph, or p-OMe-Ph groups at
the C-3 position of the pyrazolic ring were served as the starting
material for studying. The corresponding desired products 2h–2k
were produced in 77–97% yields. As a result, this efficient micro-
wave-assisted amidination method can be successfully applied to
synthesize a series of 1,3-disubstituted-methnimidamides 2a–2k.
To investigate the reactivity of the amide solvents, 5-amino-1-
3-diphenylpyrazole (1a) was used as model to react with various
amide solvents, including N,N-diethylformamide (DEF), 1-pyrroli-
dinecarboxaldehyde, and 1-piperidinecarboxaldehyde under the
same microwave-assisted condition (see Scheme 2). The corre-
sponding products 3a–3c were produced in 91–96% yields
(see the entries 1–3 of Table 2). Extension of this strategy to 5-ami-
no-1-3-diphenylpyrazole (1a) with a series of amide solvents
including N-methylacetamide, N-methylformamide, N-methylpro-
panamide, N,N-dimethylacetamide, N,N-dimethylformamide, and
N,N-dimethylbenzamide, however, provided the unexpected
amidination products 4a–4f in good to excellent yields without
forming a formyl group (86–97%, see the entries 4–12 of Table
2). The yielding formyl amidination pyrazole products seemed
determinate to the dissociation of the amide solvents.23–25
The results of the amidination of 5-amino-1,3-N,N-disubstituted pyrazoles with DMF
5-Amino-1,3-N,N-disubstituted pyrazoles Methnimidamides (2a–2k)
S.M. (1a–1k)
X
Y
Products
Yields (%)
1a
1b
1c
1d
1e
1f
1g
1h
1i
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
2a
2b
2c
2d
2e
2f
2g
2h
2i
94
82
81
90
86
83
92
97
91
95
77
o-Cl
m-Me
m-Cl
m-NO2
p-Br
p-OMe
H
H
H
H
p-Me–Ph
p-Cl–Ph
p-OMe–Ph
t-Butyl
1j
1k
2j
2k
generating the amidinyl group on the primary amine, the formyla-
tion also took place on the C-4 position of pyrazolic ring.22
The synthetic strategy was applicable to 5-amino-1-aryl-3-
phenylpyrazoles 1b–1g bearing an electron withdrawing or elec-
tron donating group on phenyl ring at the N-1 position, such as
o-Cl, m-Me, m-Cl, p-Br, p-OMe, and m-NO2. The reaction provided
the corresponding 2b–2g in good to excellent yields (81–94%
yields, see Table 1). Compounds 2a–2g were fully characterized
by spectroscopic method. For example, compound 2a presented a
The growth inhibitory activity of all methnimidamide com-
pounds is evaluated against a panel of human cancer cell lines,
including lung carcinoma (NCI-H661), nasopharyngeal (NPC-
TW01), and T-cell leukemia (Jurkat) cells. The GI50 value is the con-
centration that results in a 50% decrease in the cell growth relative
to an untreated control. Compound 2a was selected as the com-
pared model for the inhibitory activity study. The GI50 values of
peak at
d 8.69 ppm for N@C–C1H(NMe2) and a peak at d
9.69 ppm for O@C–1H in the proton NMR spectrum. In 13C NMR
spectrum, compound 2a possessed characterization absorptions
at d 185.1 ppm for aldehyde carbon O@13C and at d 159.0 ppm
for imine carbon N@13C–NMe2. Its IR spectrum showed absorption
at 1671 cmꢁ1 for –C@O stretching and 1658 cmꢁ1 for –C@N
stretching.
2a are 31.4 lM (NCI-H661), 9.3 lM (NPC-TW01), and 23.5 lM (Jur-
kat), respectively. For compounds 2b–2g containing various N-1
R1
R2
N
N
R3
R1 = H
CHO
N
N
Ph
3a-3c
O
NR2R3 = NEt2,
pyrrolidinyl, piperidinyl
R2
R1
N
NH2
R3
N
N
R1
POCl3, MW
R2
N
Ph
R1 = H, Me, Et, Ph
N
1a
R3
NR2R3 = NHMe, NMe2
N
N
Ph
4a-4f
Scheme 2.
Table 2
The results of the amidination of 5-amino-1,3-N,N-diphenylpyrazoles (1a) with amide solvents
Entry
Substrates
Amide solvents R1C(@O)NR2R3
Methnimidamides (3a–3c and 4a–4f)
R1
R2
R3
Et
Pyrrolidinyl
Piperidinyl
Me
Products
Yields (%)
1
2
3
4
8
1a
1a
1a
1a
1a
1a
1a
1a
1a
H
H
H
H
Me
Et
Me
Ph
Et
Et
3a
3b
3c
4a
4b
4c
4d
4e
4f
91
96
92
86
94
93
90
97
95
H
H
H
Me
Me
Me
Me
Me
Me
Me
Me
9
10
11
12

K.-M. Cheng et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6781–6784
6783
Table 3
Antiproliferative activity of the methnimidamide derivatives
R1
R2
N
N
R3
Z
X
N
N
Y
Compounds
Methnimidamides (2a–2k, 3a–3c, and 4a–4e)
GI50 (l
M)a,b
X
Y
Z
R1C(@N)NR2R3
NCI-H661
NPC-TW01
Jurkat
R1
R2
R3
2a
2b
2c
2d
2e
2f
2g
2h
2i
Ph
o-Cl–Ph
m-Me–Ph
m-Cl–Ph
m-NO2–Ph
p-Br–Ph
p-OMe–Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
p-Me–Ph
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
CHO
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
31.4
31.4
31.0
6.9
>50
6.7
33.4
11.9
8.6
9.3
23.3
8.9
6.4
36.7
7.4
20.2
9.7
8.1
27.2
>50
30.5
>50
24.4
>50
>50
>50
>50
20.8
23.5
26.3
9.7
8.3
>50
7.3
19.7
9.5
p-Cl–Ph
p-OMe–Ph
7.9
2j
9.9
12.5
43.5
30.0
31.3
29.0
2k
3a
3b
3c
4a
4b
4c
4d
4e
t-Bu
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
42.8
28.8
17.6
17.7
>50
>50
>50
35.1
46.7
Pyrrolidinyl
Piperidinyl
Me
H
H
H
Me
Me
>50
H
H
H
H
Me
Et
Me
Ph
Me
Me
Me
Me
>50
>50
>50
36.1
a
NCI-H661: human lung carcinoma; NPC-TW01: human nasopharyngeal carcinoma; Jurkat: human T-cell leukemia.
All tested compounds were dissolved in 100% DMSO at a concentration of 20 mM as the stock solution. Cells were cultured without or in the presence of the
b
methnimidamide derivatives at different concentrations for 72 h. Cell survival was determined by MTT assay. Drug molar concentration causing 50% cell growth inhibition
(GI50) was calculated. Each value represents the mean SD of three independent experiments.
substituted groups, 2d and 2f with m-Cl-Ph and p-Br-Ph groups
possessed the best inhibitory activity against the three cancer cell
lines with GI50 values between 6.4 lM and 8.3 lM. The results also
demonstrated they were more active against NPC-TW01 and NCI-
H661 than Jurkat. Among of methnimidamide derivatives 2h–2k
with p-Me-Ph, p-Cl-Ph, p-OMe-Ph, or t-butyl groups at C-3 position
on the pyrazolic ring, same tendency was found. The antiprolifera-
tive activities of 2h and 2i were more better than 2a, but similar to
that of 2d and 2f.
vents, and POCl3. Based on the growth inhibitory activity data,
compounds 2d and 2e with m-Cl-Ph and p-Br-Ph groups at N-1 po-
sition and 2h and 2i with p-Me-Ph and p-Cl-Ph groups at C-3 posi-
tion in pyrazolic ring possessed the most potent activity. For the
structure–activity relationship study, the formyl group at C-4 posi-
tion in the core pyrazolic ring is necessary for the inhibitory
activity.
Acknowledgments
For further investigation of the structure–activity relationship,
the antiproliferative activities of the modified amidinyl com-
We are grateful to the China Medical University (CMU98-NCTUS–
08) and the National Science Council of Republic of China for
financial support (NSC 99-2320-B-039-014-MY3).
pounds 3a–3c were tested. Compound 3c was more potent [GI50
:
17.7 M (NCI-H661), 24.4 M (NPC-TW01), and 29.0 M (Jurkat)]
l
l
l
than compounds 3a and 3b, due to the flexible six-membered pipe-
ridinyl ring which may promote the activity. In comparison with
model compound 2a (R2, R3 = methyl) and 3a–3c (R2, R3 = ethyl,
piperidinyl, or pyrrolidinyl), the bulky groups on the amidinyl moi-
ety may not favor to reach the blocking side. As a result, the anti-
proliferative activity of compounds 3a–3c was less potent than the
model compound 2a. On the other hand, compounds 4a–4e with-
out the formyl group at C-4 position on the pyrazolic ring showed
poor activity on NCI-H661, NPC-TW01, and Jurkatcells with GI50
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.08.133.
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