Labelled acetone and levulinic acid are formed when [14C]acetate is being converted to mycophenolic acid in Penicillium brevicompactum.

Evidence is presented that is compatible with the hypothesis that the farnesyl unit involved in the biosynthesis of mycophenolic acid in Penicillium brevicompactum is degraded by two successive oxidative cleavages at the double bonds distal from the phthalide nucleus. Acetone and levulinic acid are two non-aromatic degradation products.