Tuscolid and Tuscoron A and B: Isolation, Structural Elucidation and Studies on the Biosynthesis of Novel Furan-3(2H)-one-Containing Metabolites from the MyxobacteriumSorangium Cellulosum

Three novel metabolites, tuscolid (1) and tuscoron A (2) and B (3), were isolated from the myxobacterium Sorangium cellulosum (strains So ce1401 and So ce1383). The structures were elucidated by detailed NMR spectroscopic analysis, and their biosynthesis was studied by feeding C-13-labelled precursors. The results revealed that the macrolide 1 and the acyclic derivative 2 are closely related polyketides containing, as a characteristic structural feature, a furan-3(2H)-one ring system. The related minor component tuscoron B (3) was identified as an unstable structural analogue of tuscoron A. The relative stereochemistry of the tetrahydropyran ring and of C-13 to C-17 of tuscolid (1), and of the dihydropyran ring of tuscoron A (2), was determined on the basis of H-1-H-1-coupling constants and NOE correlations. A tentative mechanism for the conversion of 1 into 2 is discussed. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).