Fungal maleidrides are an important family of bioactive secondary metabolites that consist of 7, 8, or 9‐membered carbocycles with one or two fused maleic anhydride moieties. The biosynthesis of byssochlamic acid (a nonadride) and agnestadride A (a heptadride) was investigated through gene disruption and heterologous expression experiments. The results reveal that the precursors for cyclization are formed by an iterative highly reducing fungal polyketide synthase supported by a hydrolase, together with two citrate‐processing enzymes. The enigmatic ring formation is catalyzed by two proteins with homology to ketosteroid isomerases, and assisted by two proteins with homology to phosphatidylethanolamine‐binding proteins.

Three novel dimeric xanthones, cryptosporioptides A–C were isolated from Cryptosporiopsis sp. 8999 and their structures elucidated.

Deoxyscytalidin is a common biosynthetic intermediate to the nonadride scytalidin in the fungus Scytalidium album and in Diffractella curvata gives the octadride zopfiellin.