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C. Pegurier et al. / Bioorg. Med. Chem. Lett. 17 (2007) 4228–4231
4229
O
O
N
a, b
OH
c
O
O
O
O
O
O
d
N
O
N
O
N
R2
R1
O
NH
R2
O
R3
N
f
e
HN
R1
N
R2
R1
N
R2
Scheme 1. Combinatorial chemistry procedure. Reagents and conditions: (a) p-nitrophenylchloroformate, pyridine, DCM; (b) 4-piperidone, DMF;
(c) R2NH2, NaBH(OAc)3, DCE, AcOH; (d) R1CHO, NaBH(OAc)3, DCE, AcOH; (e) TFA, DCM; (f) R3COCl, NEt3, DCE.
O
recognition for the CCR3 receptor. Further focused
H
d, e
combichem libraries were then generated in order to
optimize CCR3 binding affinity by modulating R2 and
R3 substituents. A total of 790 compounds were pre-
pared by the combichem procedure. The SARs revealed
that the para-substituted phenylethyl and the ortho,
ortho-disubstituted phenyl were good modulations for
R2 and R3 moieties, respectively. In particular, com-
a, b, c
N
R
NO2
R
N
R
NH2
O
N
h
O
O
f, g
O
N
N
R3
O
R2
O
O
pound
(IC50 = 32 nM).
2
displayed
a
good activity for CCR3
R2
N
N
O
i, j
R3
N
N
R
N
O
H
R3
.HCl
N
Cl
N
R
N
O
O
Scheme 2. Medicinal chemistry procedure. Reagents and conditions:
(a) SnCl2, conc. HCl, EtOH; (b) NaNO2, conc. HCl; (c) SnCl2, conc.
HCl; (d) methyl acetoacetate, CH3CN, reflux; (e) Me2SO4, CaO,
MeOH; (f) TFA, DCM; (g) R3COCl, NEt3, DCM; (h) R2NH2,
NaBH(OAc)3, DCE, AcOH, molecular sieves; (i) paraformaldehyde,
iPrOH, NH4Cl, 90 ꢁC; (j) methanolic HCl, ether.
O
F
O
N
N
N
N
N
N
N
F
N
2
1
IC50=32 nM
IC50=158 nM
We next decided to optimize the substitution pattern on
the phenyl ring attached to the pyrazolone. Compounds
were obtained following the route depicted in Scheme 2.
Diverse pyrazolones were prepared from commercially
available hydrazines by condensation with methyl aceto-
acetate followed by N-methylation with dimethylsulfate.
Some hydrazines were prepared from nitrobenzenes by
successive reduction into anilines, diazotation, and
reduction by SnCl2 of the diazo intermediates. The
aminopiperidine core was obtained in three steps from
N-Boc-piperidone following a Boc-deprotection, acyla-
tion, and then reductive amination sequence. The pyraz-
olone moiety is incorporated in the last step via a
Mannich reaction.
a fluorine atom around the phenyl ring indicated the
meta substitution is slightly disfavored. Most com-
pounds display an IC50 around 100 nM, regardless of
the presence of electron donating (OMe, NMe2) or with-
drawing (NO2, CN) substituents. A more dramatic de-
crease in affinity is observed with the para-carboxyl
analogue 14 (IC50 = 2500 nM) suggesting that the pres-
ence of a negative charge in this area is detrimental to
the binding with the receptor.
The most potent derivative was the para-fluoro phen-
ylpyrazolone analogue 5 (IC50 = 20 nM). Interestingly,
this compound exhibits comparable level of activity in
functional assays such as the inhibition of the in vitro
Ca2+ flux and the eotaxin-induced eosinophil shape
change (IC50 = 16 nM for both). Some physicochemical
properties and in vitro metabolic clearances of com-
pound 5 were measured and are reported in Table 2,
showing poor water solubility and metabolic stability.
The binding data on human CCR3 receptor5 of com-
pounds 2–18 are reported in Table 1. By comparison
with the unsubstituted phenyl analogue 2, the results
show an overall decrease in affinity, except for the
para-fluorophenyl and the 2-pyridyl derivatives. Moving