Date of Award

2001

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Pharmaceutical Sciences

First Advisor

Lenore Martin

Abstract

In the past decade, a large number of naturally occuring thiazole and oxazole-containing peptides have been isolated from microbial and marine origins. These peptides exhibit important antimicrobial, antiviral, and anticancer activities. Solid phase synthesis of peptides provides the methods to prepare and investigate novel compounds for possible use as antibiotics. Three combinatorial peptide libraries, library 1, an enantiomeric peptide library, library 2, with guanidinium, thiazole and benzothiophene side chains and library 3, designed from a template natural product, microcin Bl 7, were tested against Vibrio anguillarum (wild type), Escherichia coli (ZK 4) and Saccharomyces cerevisiae in zone inhibition and cell culture growth inhibition assays. Library 2, with guanidinium, thiazole and benzothiophene side chains exhibited significant antimicrobial activity towards V anguillarum and E. coli, with greater activity than did the enantiomeric peptide library, library 1, or the library based on microcin Bl 7, library 3. a-Helical antimicrobial peptides act by general permeabilization of bacterial membranes. Pleurocidin, a 25 amino acid peptide was extracted from the skin secretions of winter flounder. Pleurocidin is histidine rich, forms a well-defined amphipathic a-helix and exhibits no toxicity towards eukaryotic cells. Two novel C-terminally truncated pleurocidin amide peptides were synthesized by Solid Phase Peptide Synthesis (SPPS) and their identities were confirmed by Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDl-TOF MS). The antimicrobial activities of the two C-terminally truncated peptides werecompared to pleurocidin amide against E. coli (ZK 4) and V anguillarum. Methyl 2-S-(1 '-Boc-2'-phenylethyl) thiazole-4-carboxylate can be used as a useful building block in combinatorial peptide libraries. A convenient synthesis of methyl 2-S- (1 '-Boc-2'-phenylethyl) thiazole-4-carboxylate was developed. The synthetic scheme was based on the formation of the aldehyde from Boe-phenylalanine via reduction of N-methoxy-N-methylphenylalanine. Condensation of the resulting Boc-phenylalaninal with L-cysteine methyl ester yielded methyl 2-(1 '-Boc-phenylethyl) thiazolidine-4-carboxylate in good yield. Subsequent oxidation by activated Mn02 afforded methyl 2-(1 '-Boc-2'phenylethyl) thiazole-4-carboxylate but the yields were much lower. Topoisomerases are a class of enzymes that catalyzed topological interconversions of supercoiled DNA. Inhibition of topoisomerases I or II is a target for many anticancer drugs. DNA gyrase is a type II topoisomerase unique to bacteria, and inhibition of DNA gyrase is a target for selective antimicrobial agents. Sixteen compounds of tetrapeptide library 2 were screened for their topoisomerase I, and II inhibition. The inhibition assay depended on the differential migration of supercoiled DNA versus relaxed DNA. The results were inconclusive.

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