Incubation of parthenin (1,6-beta-dihydroxy-4-oxo-10-alpha-H-ambrosa-2,11(13)-dien-12-oic acid-gamma-lactone) with the fungus Beauveria bassiana affords the C-11 reduction product, 1,6-beta-dihydroxy-11-beta-methyl-4-oxo-10-alpha-H-ambrosa-2-ene-12-oic acid-gamma-lactone. A C-11 hydroxylation product, 1,6-beta,11-alpha-trihydroxy-11-beta-methyl-4-oxo-10-alpha-H-ambrosa-2-ene-12-oic acid-gamma-lactone was obtained from the broth of the fungus Sporotrichum pulverulentum using the same substrate.