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The four theoretically possible diastereoisomeric 4 → 8 linked procyanidin dimers with two 2,3-cis-flavanoid units, epicatechin-(4β→ 8)-epicatechin (6), epicatechin-(4β→ 8)-ent-epicatechin (8), ent-epicatechin-(4α→ 8)-epicatechin (7), and ent-epicatechin-(4α→ 8)-ent-epicatechin (2), have been synthesized together with the 2,3-trans diastereoisomers catechin-(4α→ 8)-catechin (14) and catechin-(4α→ 8)-ent-catechin (15). The preferred rotamer conformations of the deca-acetate derivatives of (6), (8), (14), and (15) in chloroform were deduced from their 13C n.m.r. and high-field 1H n.m.r. spectra. The 1H n.m.r. spectra of the preferred conformers of the pairs of acetate derivatives of (6) and (15), and (8) and (14), were qualitatively similar as the relative configuration about the interflavanoid bond of one pair has a meso-relationship to the other.
Foo et al. (Sat,) studied this question.