text: Because of anisomycins wide use as a protein synthesis inhibitor, there have been many studies centered on the biosynthesis of anisomycin. One study by Butler in 1974 proposed possible precursors to this natural product. Fermentation of Streptomyces' with labeled amino acids was followed by a degradation of the radioactive anisomycin and deacetylanisomycin products to determine the locations of the labeled carbons. Although its pyrrolidine-based structure suggests that it is derived from proline, the results from the experiments indicated that tyrosine, glycine, methionine, and acetate are the primary precursors for the biosynthesis of anisomycin. Tyrosine and, to a limited degree, phenylalanine, contribute to C-2 of the pyrrolidine ring. Methionine is likely responsible for the methylation of the hydroxyl group on the aromatic ring as S-adenosylmethionine (SAM). Glycine or acetate account for C-4 and C-5 on the pyrrolidine ring. It was noted that deacetylanisomycin was a prominent product in the first few days of fermentation, suggesting that acetylation of the C-3 hydroxyl group by acetyl Co-A is the final step in the biosynthesis of anisomycin. The source of the nitrogen within the ring and C-3 were undetermined. However, C-3 is not likely to be provided by the carboxylic acid group of tyrosine because tracking of radioactivity indicated that tyrosine undergoes decarboxylation during fermentation.