Tannins and Related Compounds. CXIX. Samarangenins A and B, Novel Proanthocyanidins with Doubly Bonded Structures, from Syzygium samarangens and S. aqueum

Two proanthocyanidins named samarangenins A (1) and B (2) have been isolated, together with a variety of flavan-3-ols, proanthocyanidins and hydrolyzable and complex tannins, from the leaves of Syzygium samarangens (BLUME) MERR. et PERRY and S.aqueum (BURM f.) ALSTON (=Eugenia aquea BURM.). (Myrtaceae). Compounds 1 and 2 were characterized on the basis of spectroscopic and chemical evidence as novel dimeric proanthocyanidins, in which two flavanoid units are doubly linked through ether and carbon-carbon bonds.