THIOLYSIS OF BIRCH BARK PROCYANIDINES: STRUCTURAL DEPENDENCE IN FORMATION OF 2,3-CIS-3,4-CIS-FLAVAN-4-BENZYLTHIOETHERS FROM PROCYANIDINS

Article abstract of DOI:10.1016/0031-9422(90)80143-5

Thiolytic studies of the birch bark procyanidins, epicatechin-(4β->8)-catechin (B₁), epicatechin-(4β->6)-catechin (B₇) and epicatechin-(4β->8)-epicatechin-(4β->8)-catechin, provided, in addition to known β-thioethers, evidence for the presence of the first 2,3-cis-3,4-cis-flavan-4-benzylthioethers.Their formation is dependent on the 2,3-stereochemistry of the 'lower' terminal flavan unit and apparently on the relative lability of the interflavanoid linkage.By contrast, epicatechin-(4β->8)-epicatechin (B₂), epicatechin-(4β->6)-epicatechin (B₅) and epicatechin-(4β->8)-epicatechin-(4β->8)-epicatechin (C₁), afforded only 2,3-cis-3,4-trans-flavan-4-benzylthioethers.