BIOSYNTHESIS ON MICROBIAL METABOLITES: PART I: STUDIES ON A RED PIGMENT FROM STREPTOMYCES. PART II: TRACERS STUDIES ON ANSAMYCIN TYPE ANTIBIOTICS

SHENG-WAN LEE, Purdue University

Abstract

Part I. Studies on a Red Pigment from Streptomyces. The mechanism of antibiotic biosynthesis was examined via chemical/biochemical studies on mutants blocked along the biosynthetic pathway of a red pigment complex produced by Streptomyces coelicolor A3(2). The culture conditions for large scale production of the red pigment complex and isolation and purification procedures were worked out. Spectroscopic data indicated that the complex contains two main pigments, undecylprodigiosin and butylcycloheptylprodiginine and a minor one possibly related to dipyrrolyldipyrrolemethene. Cross feeding assays using unsubstituted pyrrole, and 2-pyrrolecarboxaldehyde, were carried out on the five mutant classes. A mutasynthesized and prodigiosin-related pigment was isolated from E class mutant fed with 3-methoxy-5-phenylpyrrole-2-carboxaldehyde. It has a novel structure distinctive from the known prodigiosins. Part II. Tracers Studies on Ansamycin Type Antibiotics. As ansamycin antibiotics, both naphthomycin and ansatrienine were isolated from Streptomyces collinus Tu 105 and Tu 1892, respectively. Their biosynthesis was studied using stable isotope and radiotracer techniques. As a prerequisite, CMR assignments of naphthomycin and the necessary degradation for ansatrienine were established for analysis of the isotope distribution. Potential precursors were prepared in ('13)C- or ('14)C-labeled form, whichever was most appropriate. ('13)C-NMR analysis of naphthomycin and ansatrienine samples biosynthesized from 3-amino-5-hydroxy-{carboxy-('13)C}benzoic acid indicated that the C(,7)N moiety in both compounds is derived from this precursor. The remainder of the naphthomycin molecule was shown to be made up of seven propionate units and six acetate units assembled in a head-to-tail fashion. This followed from feeding experiments with {1-('13)C}acetate, {2-('13)C}acetate, and {1-('13)C}propionate. An indirect incorporation of acetate into the propionate derived portions of naphthomycin possibly through methylmalonyl pathway was also observed. In ansatrienine, D-alanine, L-alanine and methionine were shown to be the precursors for the alanyl and methoxy moieties. Both shikimic acid and 2,5-dihydrobenzoic acid are specifically and efficiently incorporated into the cyclohexanecarbonyl side chain of ansatrienine probably through a sequence of dehydration and reduction reactions.

Degree

Ph.D.

Subject Area

Pharmacology

COinS