Ellagitannin chemistry. Syntheses of tellimagrandin II and a dehydrodigalloyl ether-containing dimeric gallotannin analogue of coriariin A

The first chemical synthesis of the naturally occurring ellagitannin tellimagrandin II is reported. Key steps of the synthesis include the atropselective oxidative coupling of suitably protected galloyl rings at the O(4) and O(6) positions of a glucopyranose core, and the stereoselective acylation of the derived anomeric alcohol with a galloyl chloride. In addition, the synthesis of a novel gallotannin-ellagitannin hybrid is described. This dimeric construct relied on a hetero-Diels-Alder cycloaddition/reductive rearrangement sequence to deliver the intact skeleton from a monomeric pentagalloylglucose-based orthoquinone.