An effective synthesis of isoorientin: the regioselective synthesis of a 6-C-glucosylflavone.

Isoorientin, a 6-C-beta-D-glucopyranosyl-3',4',5,7-tetrahydroxyflavone, was synthesized in a 15% overall yield, in ten steps, starting from the commercially available phloroacetophenone. The C-glucosyl phloroacetophenone derivative, a synthetic intermediate that contains a free hydroxyl group that is para to the glucosyl moiety, was obtained by hydrogenolysis by taking advantage of differences in the hydrogenolysis rates between a benzyl protecting group and a 2-methylbenzyl protecting group. Aldol condensation of the C-glucosyl phloroacetophenone derivative with 3,4-bis-benzyloxybenzaldehyde afforded the corresponding chalcone as a precursor of the 6-C-glucosyl flavone. Construction of the flavone system by application of I2-DMSO, followed by deprotection, yielded isoorientin.