638
Q.-L. Luo et al. / Bioorg. Med. Chem. Lett. 15 (2005) 635–638
not show this tendency, no matter what kind of substi-
tuent was present. For example, the most active deriva-
tive at the 5-position (36) was not as potent as its
3-position analogues (47, 48), and the most active deriva-
tive at the 4-position (40) could not match its 3-position
analogue (47). Comparison of compound 38 with 45,
and compound 39 with 44 showed the same trend. These
results may be attributed to the correct position of the
enzymeÕs pocket being near the active site, thus accom-
modating the inhibitorÕs substituents.
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In conclusion, systematic SAR studies on the PCAT
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Acknowledgements
This work was supported by the National Natural Sci-
ence Foundation of China grants 30271528 (F.-J.N.)
and 39725032 (Q.-Z.Y.), the Qi Ming Xing Foundation
of Shanghai Ministry of Science and Technology Grant
02QB14013(F.-J.N.), and the 863 Hi-Tech Program
Grant 2001AA234011(F.-J.N.), and the NIH COBRE
award 1 P20 RR15563 and matching support from the
State of Kansas (Q.-Z.Y.).