Microbiological oxidation of triterpenoids. II. 15α-Hydroxyglycyrrhetic and 7β,15α-hydroxyglycyrrhetic acids - Canonica,L.; Ferrari,M.; Jommi,G.; Pagnoni,U.M.; Pelizzoni,F.; Ranzi,B.M. (Gazz Chim Ital, 1967)