Biosynthesis of the Cytochalasans. Part III. 13C‐NMR. of cytochalasin B (phomin) and cytochalasin D. Incorporation of [1‐13C]‐ and [2‐13C]‐sodium acetate

Sequential single frequency decoupling and partially relaxed Fourier transform (PRFT) are used to assign the natural abundance 13C‐NMR. spectra of cytochalasin B (phomin) (1) and cytochalasin D (2). Cultures of Phoma spec. S 298 were fed [2‐13C]‐sodium acetate, and the distribution of this precursor in cytochalasin B (phomin) (1) was determined by 13C‐NMR. spectroscopy. Likewise, the labelling patterns in cytochalasin D (zygosporin A) (2) from Zygos‐posium masonii could be identified after incorporation of [2‐13C]‐sodium acetate and [l‐13C]‐sodium acetate. The results confirm previous proposals for the biogenesis of the cytochalasans from phenylalanine, methionine, and a C18, or C16, polyketide part.