SULFUR-SULFUR BRIDGING IN SOLID-PHASE PEPTIDE SYNTHESIS

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DESCRIPTION: Disulfide bridges play a crucial role in the folding and structural stabilization of many important extracellular peptide and protein molecules; the importance of these bonds is that they cross-link covalently portions of the polypeptide chain which are apart in the linear sequence but come together in three dimensions. The present research program builds on the twin expertises of our laboratories in mild chemical methods for solid-phase peptide synthesis and in organosulfur chemistry; within this granting period we have developed a number of novel and useful procedures for the selective protection of cysteine residues and controlled creation of sulfur-sulfur bonds in peptides. Steps can be carried out while a peptide remains anchored to a polymeric support, thereby taking advantage of the pseudo-dilution phenomenon which favors intramolecular cyclization. Solution cyclizations and those mediated by novel polymer-bound reagents are also of interest. Our multi-faceted approach assesses a repertoire of sulfhydryl protecting and/or activating groups, anchoring linkages, mild conditions for deprotection and/or cleavage and/or oxidation, and polymeric supports for applicability to these continuing challenges. Two predetermined residues are selectively deblocked, accompanied or followed either by co-oxidation or by "directed" techniques to create a pairwise cross-link. Controlled experiments test the relative influence of reaction conditions, resin substitution level, and support characteristics on the yield and purity of monomeric material. The best methods are applied to achieve the syntheses of target molecules with one to three disulfides, including oxytocin, somatostatins, conotoxins, and neutrophil defensins. As we are able to work out syntheses of the parent structures, and as appropriate, their parallel and/or anti-parallel dimers, analogs are contemplated where one or more disulfide is removed, isosterically replaced, ring size is decreased or increased, more conformational rigidity is introduced, and/or disulfides are intentionally mispaired. A proposed trisulfide modification exploits some recent advances from this research program. The covalent structures of the synthetic peptides will be verified, the secondary and tertiary structures will be studied by established biophysical techniques, and biological activities will be determined. Ultimately, chemical synthesis of rationally-designed analogs of our targeted disulfide-containing peptides, and similar work in other systems, may lead to more potent, selective, and longer-lasting drugs.