Preparation of (+)-catechin, (-)-epicatechin, (-)-catechin, (+)-epicatechin, and their 5,7,3',4'-tetra-O-benzyl analogues

摘要

Processes for preparing racemic mixtures of 5,7,3′,4′-tetra-O-benzyl-(±)-catechin and (±)-epicatechin involves (i) condensing 2-hydroxy-4,6-bis(benzyloxy)-acetophenone and 3,4-bis(benzyloxy)benzaldehyde, cyclizing the resulting compound, oxidizing the resulting compound; (ii) dihydroxylating (E)-3-(3′,4′-bis(benzyloxy)phenyl)prop-2-ene-1-ol and reducing the 1,2-diol; or (iii) coupling 3,5-bis(benzyloxy)phenol with (E)-3,5-bis(benzyloxy)-2-(3′,4′-bis(benzyloxy)phenyl)allyl)phenol and cyclizing the resulting chalcone. A process for preparing the benzylated epimers of catechin and epicatechin involves seven steps. 3,4-Bis(benzyloxy)benzaldehyde is coupled with 2-hydroxy-4,6-benzyloxy-acetophenone to form a chalcone. The chalcone is selectively reduced to an alkene. The phenolic group of the alkene is protected. The protected alkene is asymetrically dihydroxylated. The resulting compound is deprotected, cyclized, and finally hydrolyzed. Epimers resulting from these processes are chemically resolved or separated by chiral high pressure liquid chromatography. Also disclosed is a method for preparing enantiomerically pure 5,7,3′,4′-tetra-O-benzyl-(+)-catechin from a racemic mixture using dibenzoyl-L-tartaric acid monomethyl ester. Further, disclosed is an improved process for preparing dibenzoyl-L-tartaric acid monomethyl ester.