Tannins and Related Compounds. LIX. Aesculitannins, Novel Proanthocyanidins with Doubly-Bonded Structures from Aesculus hippocastanum L.

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A chemical examination of the seed shells of Aesculus hippocastanum L. has led to the isolation of proanthocyanidins A-6 (10) and A-7 (11), and aesculitannins A (12), B (13), C (14), D (15), E (16), F (17) and G (18). On the basis of chemical and spectroscopic evidence, proanthocyanidins A-6 (10) and A-7 (11) have been determined to be A-type dimers each possessing a C-4, C-6 interflavanoid linkage, while aesculitannins A (12), B (13), C (14), D (15), E (16), F (17) and G (18) have been characterized as oligomeric proanthocyanidins possessing A-type unit (s) in each molecule. In addition, the presence of (-) -epicatechin (1), proanthocyanidins B-2 (2), B-5 (3), A-2 (4), A-4 (5) and C-1 (6), epicatechin- (4β → 6) -epicatechin- (4β → 6) -epicatechin (7), and cinnamtannins B₁ (8) and B₂ (9) was also demonstrated.