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Page 182<br />

(SAR) model. The lead compound can come from compound screening, previously discovered<br />

inhibitors, or it can be <strong>based</strong> on a known substrate. The model can be obtained from x-ray<br />

crystallography, high-field nuclear magnetic resonance spectroscopy, or from homology-<strong>based</strong> model<br />

building. Inhibitor structures are developed and docked into the model of the binding site of interest,<br />

typically the active site of the enzyme. The interactions of the inhibitor-enzyme complex are evaluated<br />

and ranked. The most promising compounds are then synthesized and tested. Based on the results of the<br />

testing, additional enzyme-inhibitor structures are determined, the SAR model is updated, and the<br />

process beings again.<br />

As a model case of structure-<strong>based</strong> drug design for MMPs we will look at the design of a right-handed<br />

inhibitor <strong>based</strong> on the x-ray structures of HFC and HNC.<br />

VII. Zinc-Binding Group<br />

The design of active-site inhibitors <strong>based</strong> on the natural substrate of the collagenases has produced a<br />

variety of zinc-binding groups to anchor the inhibitor to the catalytic zinc. These group include<br />

hydroxamates, thiols, phosphorous acid derivatives (phosphinate, phosphonate, phosphoramidate), and<br />

carboxylates. The selection of a suitable zinc-binding group has been studied in depth [37–40]. The most<br />

potent zinc-binding group found for the collagenases to date is the hydroxamate.<br />

The structural comparison of hydroxamate, carboxylate, and sulfodiimine in matrilysin provided<br />

information on the contribution of the zinc ligand to the overall potency of the inhibitor [19]. The<br />

potency of the zinc-bind group can be directly related to the number of bonds in which it is involved for<br />

this instance. The hydroxamate is the perfect bidentate ligand to the zinc with both oxygens being within<br />

2.2 Å of the zinc. The hydroxamate group also is involved in hydrogen bonds with Glu219 and the<br />

carbonyl oxygen of Ala182. The carboxylate group is also a bidentate ligand to zinc, however the<br />

oxygens are not equidistant from the zinc. The carboxylate forms only one additional hydrogen bond<br />

with Glu219 of the enzyme. The sulfodiimine bound to matrilysin is a monodentate zinc ligand and the<br />

weakest of the zinc-binding groups. The comparison of several inhibitors with both carboxylate and<br />

hydroxamate zinc-binding groups demonstrates this property in fibroblast and neutrophil collagenases as<br />

well. While the potency of inhibitors with different zinc-binding groups maps directly to the number of<br />

bonds formed <strong>by</strong> the zinc-binding group, some of the increase in potency of the hydroxamate group over<br />

charged groups most likely is a result of the decreased energetic cost of the desolvation of the neutral<br />

hydroxamate.<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_182.html [4/5/2004 5:03:58 PM]

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