Biosynthesis of cyclosporin A

Abstract Short term feeding of the mould Tolypocladium inflatum with 14 C-labelled amino acids revealed a selective incorporation of l -leucine, l -valine, glycine and d , l -alanine into cyclosporins A and C. Feeding of l -[ Me - 14 C]methionine exclusively labelled the N -methyl moieties of the cyclosporins. The distribution of radioactivity from this substrate was directly proportional to the number of the relevant N -methyl amino acids in cyclosporin A, indicating a simultaneous methylation of these residues.