Ellagitannin Chemistry. Preparative and Mechanistic Studies of the Biomimetic Oxidative Coupling of Galloyl Esters

The construction of strictly the (S)-hexahydroxydiphenyl (HHDP) unit via biomimetic cyclization of suitably protected glucose-derived digalloyl esters has been achieved in good yield. Studies on substrates of increasing complexity utilizing a range of oxidants (Pb(OAc)₄, VOF₃, Tl₂O₃) have helped define the scope and limitations of this approach to ellagitannin synthesis. Computer modeling of key cyclization precursors helped elucidate the molecular-level structural details which undergird the Haslam/Schmidt biosynthesis model for this class of naturally occurring secondary plant metabolites.