The biosynthesis of manumycin type metabolites

Abstract

The biosynthesis of manumycin type metabolites has been thoroughly studied, mainly with the asukamycin producer, Streptomyces nodosus. A complete biosynthetic pathway has been elucidated from two approaches: (i) synthesizing and feeding labeled compounds to S. nodosus and the manumycin A producer, S. parvulus; (ii) tracing and isolating pathway related metabolites by feeding an isotopically labeled precursor. 3-Amino-4-hydroxybenzoic acid (3,4-AHBA) was identified as the key precursor of the mC7N unit of manumycins by synthesizing and feeding 3,4-[7- 13C]-AHBA. The discovery of a shunt metabolite, 7-(3-(N-acetylamino-4-hydroxyphenyl)-( 2E, 4E, 6E)-hepta-2,4,6-trienoic acid (85) and other type I manumycin (epoxyquinol mC7N unit) co-metabolites produced by S. nodosus helped to elucidate the biosynthetic pathway which proceeds from 3,4-AHBA by the "lower" polyketide chain extension followed by attachment of the "upper" chain and subsequently of the C5N unit. The quantitative studies on the composition of fatty acids and type I manumycins from S. nodosus revealed that the production of cyclohexanecarboxylic acid ( 39) is a rate limiting step of asukamycin biosynthesis. This limitation results in formation of shunt metabolite 85 and type I manumycin co-metabolites which differ from asukamycin at the starter unit of the "upper" chain by using branched chain starter units instead of 39. The multi-step synthesis and feeding of N1-(2-hydroxy-5-oxo-cyclopent-1-enyl)-7-[3-(7-cyclohexyl-hepta-( 2E, 4E, 6E)-trienoyl)-amino-4-hydroxyphenyl]-[1,2- 13C2]hepta-(2E, 4E, 6E)-trienamide (71) and its incorporation into asukamycin further demonstrated that oxidation/epoxidation is the last reaction on the biosynthetic pathway to the type I manumycins. The discovery of a series of new type II manumycins (hydroxyquinol mC7N unit) and the study of the fermentation course indicated that the type II manumycins produced at a later stage are formed from the type I manumycins by reduction of the epoxide.