TANNINS AND RELATED-COMPOUNDS .69. 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. aquem (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.