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Page 506<br />

Compound Width. Bulk considerations have also been examined for the phenoxy or B ring [80]. In<br />

HRV14, which has a long narrow pocket, compounds with no substituents on the phenoxy ring were the<br />

most potent. However most other serotypes were more sensitive to compounds with substituents on the<br />

phenoxy ring, either a dimethyl or a dichloro. The serotypes that preferred disubstituted compounds<br />

included HRV1A and 50, both known to have wider, shorter pockets (Table 4). This is also in agreement<br />

with the drug-clustering analysis discussed above [7].<br />

Induced VP1 Pocket Changes. The shape constrains discussed above are <strong>by</strong> nature somewhat<br />

qualitative. The precision with which one could predict the binding energy of a compound <strong>based</strong> on its<br />

shape is limited <strong>by</strong> the ability of the pocket to conform to its occupant. Conformational changes within<br />

the pocket are most pronounced between native and drug-bound HRV14, but present to a lesser extent in<br />

both HRV1A and 16. The extent of conformational changes produced <strong>by</strong> different drugs on the same<br />

virus may differ. This observation is illustrated in a study of a compound SCH 38057 in HRV14. This<br />

compound has a substantially different structure than the WIN compounds, and when bound to HRV14,<br />

induces changes in HRV14 that are also quite different from changes resulting from the binding of a<br />

WIN compound [62].<br />

The ability of compounds to effect conformational changes in the capsid when bound and the variability<br />

of these changes both between drug classes and viral serotypes have made a priori predictions of<br />

potency <strong>based</strong> on shape considerations very difficult. Comparative Molecular Field Analysis (CoMFA)<br />

studies has been useful, when examining similar compounds in a single serotype (HRV14), in<br />

demonstrating spatial constraints [85], but generalizing these constraints over many serotypes and drug<br />

classes is much more difficult.<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_506.html [4/9/2004 12:41:41 AM]

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