Stereoselective Oxidation at C-4 of Flavans by the Endophytic Fungus Diaporthe sp. Isolated from a Tea Plant

Abstract

The microbial transformation of five flavans (1—5) by endophytic fungi isolated from the tea plant Camellia sinensis was investigated. It was found that the endophytic filamentous fungus Diaporthe sp. oxidized stereoselectively at C-4 position of (+)-catechin (1) and (−)-epicatechin (2) to give the correspondent 3,4-cis-dihydroxyflavan derivatives (6, 10), respectively. (−)-Epicatechin 3-O-gallate (3) and (−)-epigallocatechin 3-O-gallate (4) were also oxidized by the fungus into 3,4-dihydroxyflavan derivatives (10, 12) via (−)-epicatechin (2) and (−)-epigallocatechin (11), respectively. Meanwhile, (−)-gallocatechin 3-O-gallate (5), (−)-catechin (ent-1) and (+)-epicatechin (ent-2), which possess a 2S-phenyl substitution, resisted the biotransformation.