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H. J. Kim et al. / Bioorg. Med. Chem. Lett. 22 (2012) 5545–5549
Scheme 1. Overall design of b-amino amide containing substitutied piperazine derivatives. Reagents: (a) EDC, HOBt, DIPEA/DMF or CH2Cl2, (b) HCl in ether/MeOH.
Table 1
DPP4 inhibition activities of various substituted compound 4
F
F
NH2
O
N
Scheme 2. Reagents: (a) R0CO2H, PyBOP, Et3N, CH2Cl2 or R0CO2Cl, Et3N, CH2Cl2; (b)
HCl in ether/MeOH.
N
F
R1
12
Compound
R1
DPP4 IC50 (nM)
trile (4f, 4g) showed 10-fold activity difference. Additional substi-
tution to compound 4i with bulky phenyl (4j) led to decrease of the
inhibitory activity.
4a
85.7
194
NO2
In case of compound 4b, from the results of mouse OGTT (oral
glucose tolerance test) study,13 it has a glucose lowering effect of
37.0%, 44.6% at the dose of 3, 10 mg/kg, respectively. It also has
good mouse pharmacokinetic profile (t1/2 = 7.06 h, BA ꢀ100%),
however the evaluation was discontinued due to the limitation of
in vivo efficacy. In mouse DPP4 inhibition assay, compound 4c
has an IC50 of 94.4 nM as well as human DPP4 inhibition study
(IC50 of 291 nM). And the compound showed excellent OGTT study
result (66% reduction of glucose AUC, at the dose of 10 mg/kg) so
dose dependent in vivo DPP4 inhibition study14 was performed.
The dose for 50% plasma DPP4 inhibition (ED50) of compound 4c
was calculated to 0.87 mg/kg (For the dose of 0.3, 1, 3, 10 mg/kg,
DPP4 inhibition % were 33.8, 52.2, 68.6 and 85.9, respectively).
But the compound 4c doesn’t have good selectivity over DPP9
(IC50 = 1763 nM, 18-fold selectivity) and has strong CYP3A4 inhibi-
tion (81.5, 94.0, 100% inhibition at the concentration of 1, 3,
4b
4c
F
F
NO2
F
291
4d
4e
264
OH
O
99.7
4f
569
10
l
M), so we stopped the assessment of the compound 4c.
Compound 4 series has some limitation with in vivo efficacy,
CN
selectivity and undesirable CYP inhibition, we designed another
series of b-amino amide which has moiety of direct carbonyl
extension at the position of -N of piperazine. This design is based
on the concept that through the carbonyl linker, direction to the
S2 pocket of DPP4 active site will be more desirable for the inhibi-
tion activity and the peptidomimetic modification will be more
susceptible to the enzymatic recognition.
The compound N-substituted piperazine with carbonyl function
group was prepared as shown in Scheme 2.
Compound 6, Commercial Boc-protected piperazine, was cou-
pled with acid or acid chloride to give compound 7. Deprotection
of Boc derivatives 6 by treatment with hydrogen chloride in ether
provided compound 8.
4g
4h
50.4
101
CN
OMe
4i
4j
103
212
OMe
F
F
The crystallographic data (PBD id: 1X70) showed that S2 pocket
in active site was composed of key amino acids with phe357,
Arg358, Ser209. And according to following molecular modeling
studies (Fig. 2), simple phenyl ring was introduced after carbonyl
unit and modification of para-position was followed for efficient
targeting on interaction with S2 pocket. Compounds in previous
SAR have little chance to make hydrophobic interaction with
Phe3576,15 and more chance to have steric hindrance with
0.05–0.5 lM. The fluoro substituted compounds 4b was less potent
than compound 4a. In compound 4c, displacement of nitro to flu-
oro resulted in further decrease of inhibitory activity. From the re-
sults of compound 4d and 4e, carbonyl group was more potent
than hydroxyl group. ortho-Substitution with phenyl and carboni-