Flavan-3-ols and procyanidins from the bark of Salix purpurea L.

From a commercial aqueous ethanolic extract obtained from the bark of Salix purpurea L. the flavan-3-ols catechin, epicatechin, gallocatechin, catechin-3-O-(1-hydroxy-6-oxo-2-cyclohexene-1-carboxylic acid)-ester, the dimeric procyanidins B1, B3 and the trimeric procyanidins epicatechin-(4B-->8)-catechin-(4alpha-->8)-catechin and epicatechin-(4beta-->8)-epicatechin-(4beta-->8)-catechin were isolated. Structure elucidation was performed by NMR, CD, MS, degradation and optical rotation methods. A fraction containing higher oligomeric procyanidins was investigated by 13C NMR. Data indicate an average degree of oligomerization of 4 to 5 flavan-3-ol units with dihydroxylated B-rings and predominance of 2,3-cis-stereochemistry.