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netLibrary - eBook Summary Structure-based Drug Design by ...

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Page 278<br />

The n=3 chain length was optimal while the nature of the tosyl group on the α- nitrogen was relatively<br />

nonspecific, with tosylGly and Nα-β-naphthylsulfonyl- Gly being of similar potency. While the phenyl<br />

group on the amide nitrogen was best, other groups were also tolerated. Although the authors did not<br />

speculate on how these compounds were bound to Factor Xa, it is reasonable to suggest that the amidino<br />

phenyl group fits in the S1 pocket similar to the orientation determined <strong>by</strong> x-ray crystallography for<br />

benzamidine in the benzamidine:thrombin x-ray crystal structure. If the aryl amidino group of 5 is<br />

matched to that of benzamidine after alignment of the catalytic triad backbone atoms (N,Cα,C) for<br />

thrombin and Factor Xa, a proposed fit of 5 to Factor Xa can be made (Figure 9) [69]. This mode of<br />

binding is consistent with the structure activity relationships observed but does not suggest the reasons<br />

for the observed small preference for Factor Xa over thrombin.<br />

Figure 8<br />

Molecular modeling fit of compound 4 in the Factor Xa active site [69]. The carbonyl of the<br />

cycloheptanone makes a hydrogen bond (3.12 Å) to N-Gly 216 .<br />

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