Microbial transformation of cycloastragenol

► A microbial biotransformation study was performed on cycloastragenol. ► Seven new biotransformation products were reported. ► The fungi provided mainly hydroxylated metabolites. ► Glomerella fusarioides ATCC 9552 provided a rare 16,24-epoxy cyclization product. ► Baeyer-Villiger oxidation by Cunninghamella blakesleeana resulted in a ring cleavage.