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Abstract:
Samples of methionine carrying a chiral CHDT-group have been prepared from and degraded chemically to chiral acetic acid. With this powerful tool inversion mechanisms were detected for the methylations on sulphur, oxygen and carbon atoms in the biosynthesis of methionine, loganin and cyanocobalamin, respectively. Chirality of the methyl group of methionine is retained during formation of the C-24 methyl group in ergosterol biosynthesis. A stereochemical scheme for the unusual course of this reaction is presented and the current stage of experiments aimed at its verification is discussed.