STRUCTURES AND BIOGENESIS OF RHOIPTELEANINS, ELLAGITANNINS FORMED BY STEREOSPECIFIC INTERMOLECULAR C-C OXIDATIVE COUPLING, ISOLATED FROM RHOIPTELEA-CHILIANTHA

Seven novel ellagitannins named rhoipteleanin A-G were isolated from t he fruits of Rhoiptelea chiliantha and their structures were unequivoc ally established on the basis of spectroscopic and chemical evidence. In the molecules of rhoipteleanin A-F, (S,S)-flavogallonyl esters span ned two glucopyranose moieties; hence, these tannins represent the fir st dimeric ellagitannins generated by stereospecific intermolecular C- C oxidative coupling between the galloyl and hexahydroxydiphenonyl gro ups. The change in the H-1-NMR chemical shifts of specific proton sign als of 1(beta)-O-galloylpedunculagin, the biogenetic precursor of rhoi pteleanin A, in deuterium oxide at various concentrations suggested th at the stereochemically regulated hydrophobic interaction between two molecules of the precursor restricts the intermolecular C-C coupling t o S-biphenyl bond formation.