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IX. S2' Interactions<br />

Page 184<br />

The interactions at the S2' site display an interesting structure-activity relationship. While the<br />

interactions do not include any hydrogen bonds, favorable stacking interactions do play a significant role<br />

in binding. A glycine residue at P2' results in a loss of three orders of magnitude in potency for<br />

otherwise identical inhibitors [41]. There is a preference for an aromatic ring at this position in natural<br />

peptide substrates [43]. Structural considerations also allow the placement of a t-butyl group here. The<br />

potency of a t-butyl glycine P2' is less than that of a phenylalanine (Table 1), but the expected gain in<br />

bioavailability brought about <strong>by</strong> shielding the amide bond from solvation effects should compensate for<br />

the loss in potency.<br />

X. Conclusions<br />

High resolution x-ray crystallographic structure determination is an essential step in structure-<strong>based</strong> drug<br />

design. The need for high resolution structural data<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_184.html [4/5/2004 5:04:31 PM]

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