Biosynthesis of the antibiotic maduramicin. Origin of the carbon and oxygen atoms as well as the 13C NMR assignments.

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Abstract
The biosynthesis of maduramicin .alpha. and .beta. in a culture of Actinomadura yumaensis was studied using 13C, 14C and 15O labeled precursors. The .alpha. component of this recently discovered polyether antibiotic, containing 47 C atoms in a 7-ring system, is derived from 8 acetate, 7 propionate and 4 methionine molecules. The .beta. component which is missing 1 methoxy group incorporates 3 methionine methyl groups. The carbohydrate moiety was enriched by methionine, but not significantly by acetate or propionate. Studies of the incorporation of 13C labeled precursors permit the 13C NMR assignment of maduramicin. The origin of O2 atoms of maduramicin was examined by feeding [1-13C, 18O2]acetate and [1-13C,18O2]propionate separately in the fermentation culture and the resulting doubly labeled maduramicin samples were analyzed by the isotopic shifts in the 13C NMR spectra. These results are consistent with the initial formation of a triene, which is converted to maduramicin by cyclization of the triepoxide.