506
Y. Zhang et al. / Bioorg. Med. Chem. Lett. 19 (2009) 502–507
Table 2
activity increased as the number of methoxy substituents in-
creased. Of the N-alkylaryl amide derivatives synthesized, the 4-
methoxyphenethyl amide 4i-6 was most potent with an IC50 value
The
l
-calpain inhibitory activities of 4-aryl-4-oxobutanoic acid amides 4i-1–4i-9
Ph
of 0.95
l
M, although its activity was slightly lesser than that of the
O
CH
O
O
3
primary amide derivative 4i-2 (IC50 = 0.52
lM). These findings sug-
2
R
N
gest that the 4-methoxyphenethyl amide group can be used in
place of a primary amide in the warhead position without causing
substantial activity loss when the synthesis of primary amide-de-
N
H
H
O
H C
3
O
4i
X
rived
l-calpain inhibitors is difficult. The removal of the C-2 car-
bonyl oxygen of inhibitors (4i-8, 4i-9) was found to reduce
inhibition, indicating that the oxygen group is required in this ser-
Compound
X
R2
Calpain inhibition IC50
3.77 0.43
(lM)
ies of compounds for
In conclusion, 4-aryl-4-oxobutanoic acid amide derivatives 4
were synthesized as acyclic structural variants of the -calpain
l-calpain inhibition.
4i-1
X = O
X = O
X = O
l
inhibitory chromone and quinolinone derivatives in order to elu-
cidate the structural requirements for inhibitor binding to the
4i-2
4i-3
H
0 52 0.01
2.35 0.13
active site of
the methoxy-substituents were more efficient at binding at the
active site of -calpain than hydrogen bond donor groups. Of
l-calpain. The hydrogen bond acceptor groups, like
OCH
OCH
3
3
l
the compounds synthesized, 4c-2, which possesses a 2-methoxy-
methoxy group in the phenyl ring and a primary amide in the
4i-4
4i-5
4i-6
4i-7
4i-8
4i-9
X = O
X = O
X = O
X = O
X = H2
X = H2
1.64 0.07
2.09 0.05
0.95 0.02
2.13 0.17
8.00 1.44
1.86 0.03
warhead
region,
most
potently
inhibited
l-calpain
OCH
3
(IC50 = 0.34
lM). These findings indicate the 4-aryl-4-oxobuta-
noic acid amide derivatives should be considered a new family
of -calpain inhibitors. Furthermore, the study also shows that
l
a 4-methoxyphenethyl amide group can be used to replace a
chemically labile primary amide in the inhibitor’s warhead
position.
OCH
3
Acknowledgments
OCH
OCH
3
3
This research was supported by the Mid-Term Technological
Development Project funded by the Korean Ministry of Commerce,
Industry and Energy (Grant No. 10027898-2007-22) and by the
Seoul Research and Business Development Program (10524).
References and notes
H
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was approximately 8-fold less potent than that of the parent chro-
mone derivative 2, but 2-fold more potent than that of quinolinone
3 to reveal that open chain structures of bicyclic chromones or
quinolinones can also bind well at the active site of l-calpain. On
the other hand, substitution of the hydroxyl group at the 2-posi-
tion of the C-4 phenyl ring reduced inhibitory activities (entries 4
and 7) indicating that the hydrogen bond donor group at the C-4
phenyl ring is more efficient at binding the active site of calpain
than the hydrogen bond acceptor –OH in this series of compounds.
Regarding amide groups in the warhead position (R2), com-
pounds derived from small primary amides were always more po-
tent inhibitors than those derived from benzyl amide. However,
primary amide-derived compounds 4d-2, 4g-2, and 4h-2, which
have a hydroxyl group at the 2-position of the C-4 phenyl ring were
not obtained probably because of their instabilities during removal
of the MOM-protecting group under acidic conditions. Therefore,
we tried to replace the unstable primary amide group with
N-alkylaryl amide groups in the warhead region; the inhibitory
activities of the resulting compounds are summarized in Table 2.
The 4-(2,5-dimethoxyphenyl)-4-oxobutanoic acid was chosen for
this study because of the ready availability by simple Friedel–
Crafts reaction of 1,4-dimethoxybenzene with succinic anhydride
and the potent inhibitory activity of its derivative 4i-2. In terms
of the benzyl amide derivatives, it was observed that the inhibitory
9. Shirasaki, Y.; Yamaguchi, M.; Miyashita, H. J. Ocul. Pharmacol. Ther. 2007, 22,
417.
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15. Spectral data of selected compounds. Compound 4c-2: 1H NMR (400 MHz,
DMSO-d6) d 8.33 (d, J = 7.2 Hz, 1H, –NH), 8.00 (s, 1H, –NH), 7.76 (s, 1H, –NH),
6.95–7.54 (m, 9H, aromatic), 5.29 (s, 2H, –OCH2O–), 5.19 (m, 1H, –NH–CH–CH2–
Ph), 3.39 (s, 3H, –OCH3), 3.07–3.12 (m, 2H, –CH2–), 2.74 (dd, J = 14.0, 9.6 Hz, 1H,
–CH–CH2Ph), 2.43–2.49 (m, 3H, –CH2–, –CH–CH2Ph); 13C NMR (100 MHz,
DMSO-d6) d 200.9, 197.4, 172.0, 163.2, 155.8, 138.0, 133.7, 130.0, 129.5 (2C),
129.1, 128.7 (2C), 126.9, 121.9, 115.6, 94.6, 56.6, 55.5, 38.9, 35.7, 29.6.
Compound 4i-2: 1H NMR (400 MHz, DMSO-d6) d 8.34 (d, J = 7.2 Hz, 1H, –NH),
8.02 (s, 1H, –NH), 7.78 (s, 1H, –NH), 7.07–7.31 (m, 8H, aromatic), 5.19
(m, 1H, –NH–CH–CH2–Ph), 3.82 (s, 3H, –OCH3), 3.73 (s, 3H, –OCH3), 3.02–3.12
(m, 3H, –CH2–, –CH–CH2Ph), 2.74 (dd, J = 14.0, 9.6 Hz, 1H, –CH–CH2Ph), 2.41–
2.45 (m, 2H, –CH2–); 13C NMR (100 MHz, DMSO-d6) d 200.2, 197.5, 172.0,
163.2, 153.3, 153.0, 138.1, 129.5 (2C), 128.7 (2C), 128.3, 126.9, 119.8, 114.5,
114.1, 56.7, 56.0, 55.5, 39.0, 35.7, 29.6. Compound 4i-6: 1H NMR (400 MHz,