In a study of the stereo-electronic requirements for microbiological h
ydroxylation by Rhizopus stolonifer, ent-19-hydroxygibberell-16-en-20-
oic acid 20,19-lactone, ent-7,19-dihydroxygibberell-16-en-20-oic acid
20,19-lactone and ent-19-hydroxygibberell-16-en-7,20-dioic acid 20,19-
lactone 7-methyl ester are shown to be hydroxylated at the 15alpha-pos
ition.