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Page 276<br />

In both cases the acids are much more selective for Factor Xa over thrombin. An initial modeling study<br />

using a homology-built Factor Xa structure proposed a fit of DX9065a to Factor Xa in which the<br />

amidinoary1 group occupies the S1 pocket and the acetimidoyl group is directed out of the S4 pocket<br />

[60].<br />

Lin et al. [64] have provided a more systematic study of possible fits of compound 2 and DX9065a<br />

using the recently available Factor Xa coordinates [4]. After aligning the His 57, Ser 195, and Asp 102<br />

backbone atoms for Factor Xa and thrombin (in the benzamidine:thrombin x-ray structure [65]) the<br />

arylamidino group of 2 was superimposed on the benzamidine template and a systematic conformational<br />

search was performed on the rotatable bonds of inhibitor 2. Energetics and complementarity to the<br />

Factor Xa surface determined a saved set, about 300 low-energy conformations, for further study. The<br />

final result was an optimized structure in which the acetimino group of 2 fits into<br />

Figure 7<br />

Molecular modeling fit of compound 2 with the arylamidino group positioned in the S1<br />

pocket and the acetimino group in the S4 cation-π site [69].<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_276.html (1 of 2) [4/5/2004 5:13:12 PM]

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