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Abstract
Reactions of polymeric procyanidins with phloroglucinol at pH 12.0 and temperatures of 23 or 50°C gave epicatechin-(4β)-phloroglucinol (7), by cleavage of the interflavanoid bond between procyanidin units with subsequent addition of phloroglucinol, and (+)-catechin from the terminal unit. The phloroglucinol adduct (7) rearranged to an enolic form of 8-(3,4-dihydroxyphenyl)-7-hydroxy-6-(2,4,6-trihydroxyphenyl)bicyclo[3.3.1]nonane-2,4,9-trione (9). Rearrangement of a dimeric procyanidin phloroglucinol adduct resulted in the formation of 3'-{8-(3,4-dihydroxyphenyl)-7-hydroxy-2,4,9-trioxobicyclo[3.3.1]nonan-6-yl}-4-(3,4-dihydroxyphenyl)-2',3,4',5,6',7-hexahydroxyflavan (10), also in an enolic form. (+)-Catechin, from the terminal unit, gave catechinic acid, an enolic form of 6-(3,4-dihydroxyphenyl)-7-hydroxybicyclo[3.3.1]nonane-2,4,9-trione (4).
Citation
Laks, Peter E.; Hemingway, Richard W.; Conner, Anthony H. 1987. Condensed tannins. Base-catalysed reactions of polymeric procyanidins with phloroglucinol: Intramolecular rearrangements. Journal of the Chemical Society Perkin Trans. I. 1875-1881
