Biosynthetic incorporation of labeled sodium acetate into oxosorbicillinol in Trichoderma sp. USF-2690 suggests that oxosorbicillinol is derived from six acetate units, and subsequent bioconversion of the labeled oxosorbicillinol to bisvertinolone in the fermentation of the strain suggests that bisvertinolone is biosynthesized from oxosorbicillinol and sorbicillinol in a Michael-type reaction.