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

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Page 23<br />

potentially lowering the desolvation penalty. The absence of hydrogen-bonding interactions with the<br />

carbonyl oxygens of Gly27/27' was viewed as a positive factor, since the accumulated structural and<br />

mechanistic information suggested that formation of these hydrogen bonds may not be energetically<br />

favorable [23]. The compound was synthesized as a racemic mixture of two enantiomers of the central<br />

hydroxymethyl group and had the inhibition constant of 24 μM. Despite the modest binding constant of<br />

compound II (Table 6) and very low water solubility, the co-crystal structure with HIV PR was solved at<br />

2.3 Å resolution, providing a critical starting point for further design. The inhibitor was found to bind<br />

largely as anticipated with the two aromatic rings occupying the S1 and S1' subsites and the two<br />

benzamide carbonyls forming hydrogen bonds to the flap water Wat301. Both benzamide nitrogens<br />

interact via a string of highly ordered water molecules with the amide nitrogens of Asp29/29'. The<br />

crystal structure of the complex indicated that the S enantiomer was the more active component of the<br />

racemic mixture and this was confirmed <strong>by</strong> stereoselective synthesis of subsequent compounds [44].<br />

In the subsequent designs, the ortho-substituted benzyl rings were consecutively replaced <strong>by</strong> larger<br />

naphthyl groups that occupied more of the S1–S3 and S1'–S3' subsites. The increased area of<br />

hydrophobic interactions with the residues in these subsites was reflected in a substantial improvement<br />

in the<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_23.html [4/5/2004 4:45:41 PM]

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