Tannins and Related Polyphenols of Melastomataceous Plants. I. Hydrolyzable Tannins from Tibouchina semidecandra COGN.

Abstract

Four new hydrolyzable tannins, methylvescalagin and nobotanins, A, D and F, along with eleven known polyphenolics, have been isolated from the leaves of Tibouchina semidecandra COGN. Based on spectral and chemical evidence, nobotanin D was characterized as 1, 6-di-O-galloyl-2, 3-O-(S)-hexahydroxydiphenoyl-β-D-glucose (16), and the structures of nobotanins A (17) and F (18) were established as dimeric hydrolyzable tannins possessing a valoneoyl group as a linking unit between the monomers.