Use of 13 C in biosynthetic studies. Location of isotope from labeled acetate and formate in shanorellin by 13 C nuclear magnetic resonance spectroscopy.

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Cultures of the ascomycete Shanorella spirotricha supplemented with 13C-iabeled acetate and formate produced 13C-enriched shanorellin (2,6-dimethyl-3-hydroxymethyl-5-hydroxy-1,4-benzoquinone). The distribution of isotope in shanorellin was determined by 13C nuclear magnetic resonance spectrometry. [1-13C]acetate labeled C-1 C-3, and C-5, and [2-13C]acetate labeled C-2, C-4, C-6, and the hydroxymethyl, while [13C]formate labeled the two methyl carbon atoms. The results confirm that shanorellin is biosynthesized from four molecules of acetate, with loss of one carboxyl group and addition of two methyl groups from a one-carbon donor. The labeling pattern is consistent with its formation via the acetate–polymalonate pathway although a malonate supplement was not specifically incorporated into the chain-extending units.