Microbial oxidation and glucosidation of echinocystic acid by Nocardia corallina

Echinocystic acid (3β,16α-dihydroxy-olean-12-en-28-oic acid 1) is a complex compound with many bioactivities. Microbial transformation of echinocystic acid (1) by Nocardia corallina CGMCC4.1037 has been studied. Incubation of echinocystic acid with N.corallina CGMCC4.1037 afforded three metabolites: 3-oxo-16α-hydroxy-olean-12-en-28-oic acid (2), 3β,16α-dihydroxy-olean-12-en-28-oic acid 28-O-β-d-glucopyranoside (3), and 3-oxo-16α-hydroxy-olean-12-en-28-oic acid 28-O-β-d-glucopyranoside (4). Product (4) was a new product. Their structure elucidation was mainly based on the HRMS and NMR data. The possible mechanism of the regio-selective oxidation of the 3-OH and a probable sequence of these transformations were also discussed. This is the first report on the microbial transformation of echinocystic acid (1). This method may open a new route to the future modification of echinocystic acid (1).