Microbial hydroxylation of (±)- and (-)-(2Z,4E)-5-(1′,2′-epoxy-2′,6′,6′-trimethylcyclohexyl)-3-methyl-2,4-pentadienoic acid into (±)- and (-)-xanthoxin acid by Cunninghamella echinulata

Microbial hydroxylation of (+/-)-(2 Z, 4E)-5-(1', 2'-epoxy-2', 6', 6' -trimethylcyclohexyl)-3-methyl-2, 4-pentadienoic acid (3a) with Cercospora cruenta, a fungus producing (+)-abscisic acid, gave a four-stereoisomeric mixture consisting of (+)- and (-)-santhoxin acid (4a), and (+)- and (-)-epi-xanthoxin acid (5a) bg an HPLC an:analysis with a chiral column. Screening of the microorganisms capable of oxidizing (+/-)-3a showed that Cunninghamella echinulata stereoselectively oxidized (+/-)-3a to xanthoxin acid (4a) with the some degree of enantioselectivity as (-)-3a to (-)-4a.