Biosynthesis of the Cytochalasans. Biosynthetic studies on chaetoglobosin A and 19‐ O ‐acetylchaetoglobosin A

Incorporation of [1‐ 13 C]‐, [2‐ 13 C]‐ and [1,2‐ 13 C 2 ]‐acetate, [1‐ 13 C]‐propionate, [ 13 C‐CH 3 ]‐ L ‐methionine and [3‐ 14 C]‐ DL ‐tryptophan into chaetoglobosin A ( 1 ) and 19‐ O ‐acetylchaetoglobosin A ( 2 ) by Chaetomium globosum demonstrated that the building blocks of 1 and 2 are 9 and 10 units of acetate/malonate respectively, 3 units of methionine and 1 unit of tryptophan. Propionate is incorporated indirectly after several biological transformations. Using [2‐ 13 C, 2‐ 2 H 3 ]‐acetate as precursor, the starter unit of the polyketide‐chain was identified. Experiments which [ 13 C, 2 H 3 ‐CH 3 ‐ L ‐methionine demonstrated that the three C ‐methylations occur with retention of all three H‐atoms of the methyl group. Incorporation experiments with various 14 C‐ and 3 H‐labelled tryphtophan samples and with [2‐ 2 H]‐ and [2‐ 15 N]‐ L ‐tryptophan showed that the amino acid is incorporated intact with retention of both the α‐H‐ and the α‐N‐atom. On the basis of these results a more detailed general scheme of the cytochalasan biogenesis is proposed.