Biosynthetic formation of the S-methyl group of the angucycline antibiotic urdamycin E

Biosynthetic studies on the angucycline antibiotic urdamycin E (1), produced by Streptomyces fradiae (strain Tü 2717), resulted in methionine being the precursor of the S-methyl group which is transfered in a unique way as an intact unit from methionine thus showing a new structural element biogenetically deriving from this amino acid; the discussed mechanism for this unusual reaction is an enzymatic cleavage of methionine yielding SMe^- which attacks the electrophilic 5,6-double bond of the (1)-precursor urdamycin A (2), thus forming (1) by a non-enzymatic Michael addition followed by a proton rearrangement and oxidation by molecular oxygen.