T. Mizuhara et al. / Bioorg. Med. Chem. Lett. 23 (2013) 4557–4561
4559
Table 3
Cl
Cl
R
Cl
NHCOEt
Structure–activity relationship of the pyrazole moiety
a
d
R1
R2
NHCOEt
OH
CO2H
15
CO2H
R
N
16 (R = NO2)
17 (R = NH2)
18 (R = NHCOEt)
19 (R = CH2OH)
20a (R = CHO)
N
N
b
e
H
R3
c
Cl
OR
OH
OH
Compound
R1
R2
R3
EC50 (lM)
a
Cl
NO2
Me
Me
a
NO2
f
7
3
Me
H
Me
Me
Me
Et
CN
CN
H
CN
CN
CN
CN
CO2Me
Ph
Ph
Ph
Me
0.36 0.11
>1.0b
>10
29a
29b
29c
29d
29e
29f
29g
CHO
20e (R = H)
20b (R = Me)
CHO
21
CHO
20d
>10
g
c-hexyl
>1.0b
>10
Ph
Ph
Ph
OH
Ph
Me
>10
OH
Cl
Cl
CONHEt
f
>1.0b
R
a
EC50 values represent the concentration of the compound required to inhibit the
HIV-1 infection by 50%. The data were obtained from three independent
CHO
20h
22 (R = CO2H)
23 (R = CONHEt)
experiments.
h
b
Cytotoxicity was observed at 10 lM.
Me
CN
Me
CN
R1
R2
R1
R2
i
i or j
N
N
R1
N
R2
NH2
R1
N
R2
N
N
H
N
14
N
R1
R2
H
NHCOEt
OH
a
b
Cl
R3
N
N
N
EtO
CN
H
R3
R3
13 (R1 = Me, R2 = CN)
24a (R1 = NHCOEt; R2 = H)
24h (R1 = CONHEt; R2 = OH)
25b-e (R1 = NO2)
Cl
27a (R1 = H, R2 = CN)
k
l
28a-g (R3 = Ph, Me, c-hexyl)
29a-g
31a-q
26b-e (R1 = NH2·HCl)
24b-d (R1 = NHCOEt)
(R1 = Me, R2 = H)
30a-q (R3 = Ar)
27b
27e (R1 = Et, R2 = CN)
27f (R1 = Ph, R2 = CN)
Me
CN
Me
CN
(R1 = Me, R2 = CO2Me)
27g
NH2·HCl
OH
NHCO-R
m
N
N
Me
CN
Me
CN
N
N
N
N
OH
H
H
NHCOEt
OH
NHCOEt
OH
N
N
c
Cl
Cl
N
N
N
N
H
H
Cl
Cl
26e
24e (R = Me)
(R = n-Pr)
24f
Br
Ar
(R = n-pentyl)
24g
31c
32a-m
Scheme 2. Synthesis of compounds 24a–h with a variety of substituted benzyl-
amine moieties. Reagents and conditions: (a) H2SO4, HNO3, 0 °C to rt; (b) Fe, NH4Cl,
i-PrOH, H2O, 90 °C; (c) EtCOCl, Et3N, THF, 0 °C to rt; (d) EtOCOCl, Et3N, THF, ꢂ10 °C,
then NaBH4, MeOH, 0 °C to rt; (e) PCC, CH2Cl2, rt; (f) hexamethylenetetramine,
AcOH, 130 °C; (g) MeI, K2CO3, DMF, rt; (h) CBr4, Et3N, EtNH2, PPh3, CH2Cl2, rt; (i) 20,
PPTS, toluene, reflux, then LiBH4, THF, 0 °C to rt; (j) 20, TsOH, toluene, reflux, then
NaBH4, EtOH, 0 °C to rt; (k) FeCl3, NH2NH2ꢁH2O, activated carbon, i-PrOH, 80 °C, then
4 M-HCl/1,4-dioxane; (l) EtCO2H, EDC, HOBt, (i-Pr)2NEt, DMF, 45 °C; (m) RCO2H,
EDC, HOBt, (i-Pr)2NEt, DMF, 45 °C.
Scheme 3. Synthesis of compounds 29a–g, 31a–q, and 32a–m with a variety of N-
arylpyrazole and N-alkylpyrazole moieties. Reagents and conditions: (a) R3-NHNH2,
EtOH, rt; (b) 10, PPTS, toluene, reflux, then LiBH4, THF, 0 °C to rt; (c) Ar-B(OH)2 or
Ar-Bpin, Pd(dba)2, PCy3, K3PO4, 1,4-dioxane, H2O, 80 °C.
meta-position of the N-phenyl ring with methyl (31b), fluoro
(31d), or phenyl groups (31g) resulted in comparable or more po-
tent anti-HIV activity (EC50 = 0.37, 0.33 and 0.13 lM, respectively)
to that of compound 3, whereas a significant decrease in anti-HIV
activity was observed following the introduction of a methoxy
(31a), nitro (31f), or acetamido group (31h). Anti-HIV activity of
bromo (31c) or trifluoromethyl (31e) derivatives could not be
determined because of their significant cytotoxicity. The methyl
modification at the ortho- and para-positions (31i and 31j) afforded
We next examined substituent effects on the left pyrazole part
of compound 3 (Tables 3–5). A variety of 5-aminopyrazoles 28a–g
and 30a–q were prepared by reaction of 3-ethoxyacrylonitrile
derivatives (13 and 27) with aryl- or alkyl-hydrazines (Scheme 3).
Reductive amination of 28a–g and 30a–q with benzaldehyde 10
provided the series of pyrazole derivatives 29a–g and 31a–q. 1-
Biaryl-5-aminopyrazole derivatives 32a–m were synthesized using
a Suzuki–Miyaura cross-coupling reaction of compound 31c with
aryl boronic acid or the pinacol ester.
reduced anti-HIV activities (EC50 >1.0
3,5-dichlorophenyl group showed no antiviral activity (EC50 >1.0 -
M). In addition, replacement of the phenyl group with naphthyl
(31l and 31m), 3-pyridyl (31o), or quinolinyl group (31p and
31q) failed to improve anti-HIV activity (EC50 >1.0 M). 2-Pyridyl
lM). Compound 31k with a
l
l
Removal of the 3-methyl or 4-cyano group on the pyrazole 3 re-
derivative 31n showed unexpected levels of cytotoxicity.
duced anti-HIV activity (29a and 29b, EC50 >1.0 lM), as shown in
The optimization studies indicated that the introduction of a
biphenyl-3-yl group on the pyrazole moiety (31g) effectively im-
proved the anti-HIV activity. To develop more potent anti-HIV
agents, we extended the structure–activity relationship investiga-
tions to the modified aryl groups onto the N-phenylpyrazole moi-
Table 3. In addition, no potent derivatives were obtained by all of
our attempts including substitutions of the N-phenyl group with
alkyl groups (29c and 29d), substitutions of the 3-methyl group
with either an ethyl (29e) or phenyl group (29f), and substitution
of the 4-cyano group with a methoxycarbonyl group (29g).
We turned to examine the structure–activity relationship of the
N-aryl moiety on the pyrazole (Table 4). The modification at the
ety (Table 5). We designed and synthesized
a variety of
methoxyphenyl, tolyl or chlorophenyl derivatives (32a–i). Among