Use of 13C in biosynthetic studies. The labelling pattern in tenellin enriched from isotope-labelled acetate, methionine, and phenylalanine

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Abstract
The biogenetic origin of the C atoms in tenellin was established by adding 13C-enriched compounds to cultures of Beauveria bassiana and determining the isotopic distribution in the metabolite by 13C NMR spectrometry. Tenellin was formed by condensation of an acetate-derived polyketide chain with a phenylpropanoid unit that may be phenylalanine. Alternate C atoms of the polyketide chain were labeled with sodium [1-13C]- and [2-13C]-acetate; sodium [1,2-13C]acetate was incorporated as intact two C units, the presence of which in tenellin was apparent from coupling between adjacent 13C-enriched carbons. Substituent methyl groups of the polyketide-derived alkenyl chain were labeled with L-[Me-13C]methionine. The labeling patterns from DL-[carboxy-13C]phenylalanine and DL-[.alpha.-13C]phenylalanine indicated a rearrangement of the propanoid component at some stage in the synthesis. The mass spectrum of tenellin from cultures administered L-[15N]phenylalanine showed isotopic enrichment similar to that obtained with 13C- or 14C-labeled phenylalanine. During incorporation of L-[carboxy-14C, .beta.-3H]phenylalanine, 96% of the tritium label was lost, discounting the possibility of a 1,2-hydride shift during biosynthesis of the metabolite.

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