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

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Document<br />

Page 533<br />

the reactions are to be implemented with the template attached to a solid support. When the synthesis is<br />

optimized and fully automated, thousands to millions of compounds are accessible.<br />

One of the key features of this process is that all of the compounds that can potentially be made <strong>by</strong><br />

elaboration of a custom scaffold are first “made” in virtual form in a computer. Each of the chemical<br />

reactions required to create the library is encoded in a program that then systematically combines the<br />

template and the building blocks to create a 2-dimensional representation of each member of the library.<br />

Next, 3-dimensional representations are created and molecular-property descriptors are calculated for<br />

each member of the library. Molecular property descriptors encompass molecular connectivity, dipole<br />

moments, calculated partition coefficients, and many other calculable molecular properties. The virtual<br />

library of compounds can then be computationally screened and the library members ranked according<br />

to their ability to interact with the target receptor or 3-dimensional pharmacophore model [23–25]. The<br />

compounds can also be ranked <strong>by</strong> their inability to interact with any number of alternative targets whose<br />

inhibition is undesirable, or their ability to meet any range of desired chemical or physical properties<br />

that may be important in drug pharmacology. Alternately or additionally, compounds can be ranked<br />

according to their ability to span or sample the physical-chemical property space to produce the most<br />

diverse set of compounds for initial screening [26,27].<br />

Small sublibraries of the large virtual library that best satisfy the selection criteria are chemically<br />

synthesized using automated methods and then the biological and/or chemical properties of each<br />

compound are measured using automated assays. The SAR data that emerge from the assays are stored<br />

in a central database and used in the selection process to drive additional rounds of sublibrary selection,<br />

synthesis, and assay. Multiple mathematical models are developed to correlate the computed structure<br />

and properties of each synthesized library member with the biological, chemical, or physical properties<br />

that are measured during each cycle of testing [28]. A key feature of this approach is that compounds<br />

can be selected not only on the basis of which are predicted to perform the best in the target assay but<br />

also on the basis of their ability to perform the best in the target assay but also on the basis of their<br />

ability to distinguish between or validate the SAR models that are generated. The observed and<br />

predicted properties of a given sublibrary are compared so that the set of assumptions upon which<br />

property refinement is <strong>based</strong> is constantly updated. In principle, this process can become completely<br />

automated so that leads are discovered and refined with very little manual intervention [28].<br />

To achieve the greatest improvements in drug discovery efficiency, empirical data of various kinds must<br />

be collected throughout the iterative refinement process. It is desirable to obtain more accurate<br />

dissociation constants rather than IC 50 or single-point percent-inhibition values. In addition, the 3dimensional<br />

structures of interesting target—inhibitor complexes are determined<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_533.html [4/9/2004 12:50:11 AM]

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