Conformational studies of (−)-epicatechin-Mosher ester

An in depth ab initio investigation into the factors governing the conformational behaviour of α-methoxy-α-trifluoromethyl-α-phenylacetic acid (MTPA) esters, extensively utilized to determine the absolute stereochemistry of secondary alcohols and amides, discloses the hyperconjugative interactions responsible for the important syn- and anti-periplanar conformational rigidity and the predominance of the former over the latter. The first flavonoid-Mosher ester crystal structure is reported.

The crystal structure of (−)-epicatechin-(R)-MTPA is described and the origin of the conformational behaviour observed for MTPA esters is explained.