10.12.2012 Views

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

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

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

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Document<br />

A. Molecular Diversity and Screening-Based Identification of Nonpeptide Ligands<br />

Page 586<br />

Precedence for the success of nonpeptide drug discovery can be traced to the identification of morphine<br />

(75; Figure 17) as nonpeptide natural product agonist at μ-opioid peptide receptors [90]. To date, the<br />

robust momentum of nonpeptide drug discovery continues to be accelerated <strong>by</strong> sophisticated<br />

biochemical screening technologies. The scope of molecular diversity as well as therapeutic targets for<br />

such screening-<strong>based</strong> nonpeptide ligand lead compounds includes the following examples (Figure 17):<br />

substance P (NK 1 antagonist, 76 [91]; angiotensin AT 1 antagonist, 77 [92]; growth hormone-releasing<br />

peptide (GHRP) agonist, 78 [93]; cholecystokinin CCK A antagonist, 79 [94]; CCK B/gastrin antagonist,<br />

80 [95]; CCK A agonist, 81 [96]; endothelin antagonist, 82 [97]; gonadotropin-releasing hormone<br />

(GnRH) antagonist, 83 [98]; vasopressin V 1 antagonist, 84 [99]; gastrin-releasing peptide antagonist, 85<br />

[100]; glucagon antagonist, 86 [101], neurotensin antagonist, 87 [102]; angiotensin AT 1 agonist, 88<br />

[103]; oxytocin antagonist, 89 [104]; and HIV protease inhibitor, 90 [105]. A significant number of<br />

screening-derived nonpeptide leads have been identified for G-protein-coupled receptors (GPCRs), and<br />

in a majority of cases these compounds have been determined to be competitive antagonists. Albeit the<br />

3D structures of this receptor superfamily have not been directly determined, homology model-building<br />

and site-directed mutagenesis studies are impacting structure-activity analysis of agonist and antagonist<br />

ligands (peptide, peptidomimetic, and nonpeptide) for several GPCR targets (see below).<br />

B. Nonpeptides: Exploring Pharmacophore Relationships to Peptide Ligands<br />

Relative to a number of GPCR targets, there exists significant opportunity to compare chemical<br />

structures and 3D pharmacophore models of both peptide and nonpeptide ligands. Such comparative<br />

analyses can explore the possibility of similar 3D substructural elements that may account for their<br />

molecular recognition at the binding site(s) of the receptor. The fact that a vast number of screeningderived<br />

nonpeptide leads are multifunctionalized 5- to 7-membered ring heterocycles (e.g., alkaloid and<br />

benzodiazepine) and contain conformationally rigid substructural elements (e.g., biphenyl, spiro-bicyclic<br />

rings, and N-substituted amide or amine linkages) suggests the likelihood that such compounds are<br />

binding with highly favorable entropic driving forces as compared to the more conformationally flexible<br />

peptide ligands. In this regard, efforts to “rigidify” peptide-<strong>based</strong> scaffolding or replace it <strong>by</strong> nonpeptide<br />

templates has been the underlying theme of peptidomimetic design strategies, and concepts for the latter<br />

approach date back to the proposed used of cycloaliphatic ring systems that might be<br />

multifunctionalized to create “topographi-<br />

http://legacy.netlibrary.com/nlreader/nlReader.dll?bookid=12640&filename=Page_586.html [4/9/2004 1:16:39 AM]

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!