The biosyntheses of seseandelin (1) and sescandelin B (2) were studied by feeding of [C-13]labelled precursors to Sesquicillum candelabrum. The labelling pattern of those compounds enriched from the [1-C-13], [2-C-13], and [1,2-C-13]acetates, and from the [C-13]formate showed that both compounds were derived from a pentaketide chain and a C-1 unit. The isocoumarin skeleton of 1 and 2 is considered to have been formed by the cyclization of a pentaketide chain and a C-1 unit, and of a pentaketide, respectively.
