Biosynthesis of Ganefromycin:  Results from Blocked Mutants and Bioconversion Experiments

Abstract

The biosynthetic pathway of ganefromycin alpha (8) was investigated using blocked mutants of Streptomyces lydicus spp. tanzanius, the ganefromycin alpha producer, in conjunction with bioconversion experiments with the products of these mutants. Compounds 1-7 and 9-15, which are structurally related to ganefromycin alpha, were produced by cultures of secretor mutants showing blockage or diminished production of 8. These compounds were isolated, characterized, and subjected to bioconversion experiments using converter and other secretor mutants. Some of the compounds were shown to be products resulting from blocks at various stages in the biosynthetics pathway beyond construction of the polyketide skeleton (e.g., furan ring closure, hydroxylation, glycosylation, etc.). Other compounds were not bioconverted by biosynthetically capable mutants and were deemed shunt products. A mutant's metabolites and bioconverting ability were used to surmise the location of the block. A picture of the later sequence of events leading to the synthesis of ganefromycin alpha emerged, including C23-hydroxylation, C13a-O-methylation, C21a-hydroxylation, and C21a-O-glycosylation. Some of the later steps in the biosynthetic pathway for ganefromycin alpha are proposed.

Biosynthesis of polyketides by trans-AT polyketide synthases

“…The post-PKS steps in the biosynthesis of ganefromycins 234-237 were investigated in studies by Carter and coworkers. 394,415 When the methyltransferase inhibitor sinefungin was added to cultures of the producer Streptomyces lydicus, a series of new ganefromycins was produced that lacked the O-methyl group at C13. 394 In addition, some compounds carried only a single unmethylated sugar unit, suggesting that the glycosyltransferase(s) that add further sugars recognizes only methylated precursors.…”

“…Another approach used by these researchers consisted of generating random mutants of the producer strain by treatment with the mutagenizing agent N-methyl-N 0 -nitro-Nnitrosoguanidine. 415 The compounds resulting from blocked biosynthesis were arranged in a biosynthetic order by crossfeeding experiments, which revealed a post-PKS route as shown in Fig. 41.…”

“…Several additional polyketides that are likely shunt products were also identified in this study. 415 tunicate and its symbionts, providing yet another example for the importance of trans-AT systems for the secondary metabolism of symbionts. The available sequences can now be used to isolate the entire gene cluster(s) and to predict the product.…”

Isolation and Preliminary Charactrization of Strptomyces Flavopersicus Mutants Blocked in Spectinomycin Biosynthesis

“…Detailed characterization of the erythromycin pathway has 27 been performed on the basis of blocked mutants and cosynthesis experiments (16,18). The biosynthetic pathway of ganefromycin was investigated using blocked mutants of Str.lydicus in conjunction with bioconversion experiments with the products of these mutants (7).…”

Novel Amination and 1,2-Amino,hydro-Elimination between 2,3-Diketopyrido[4,3,2-de]quinolines and Primary Amino Compounds

“…For example, the pyrido[4,3,2- de ]quinoline core structure has been found in many sponges and tunicates (Chart ). The chemistry and pharmacological properties of these marine natural products have been the subject of much current interest. , Many of these marine products have generated interest both as challenging problems for structure elucidation − and synthesis, − as well as for their biological activities. − …”