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 tellim agrandin II is reported. Key steps of the synthesis include the atropselect ive oxidative coupling of suitably protected galloyl rings at the O(4) and O(6) positions of a glucopyranose core, and the stereoselective acylation o f the derived anomeric alcohol with a galloyl chloride. In addition, the sy nthesis of a novel gallotannin-ellagitannin hybrid is described. This dimer ic construct relied on a hetero Diels-Alder cycloaddition/reductive rearran gement sequence to deliver the intact skeleton from a monomeric pentagalloy lglucose-based orthoquinone.