Synthetic study of doubly-linked oligocatechins
Pages Oral24-
Details
Pages Oral24-
The A-type procyanidins, such as procyanidin A2 (1) and cinnamtannin B1 (2), are unique among the oligomeric catechins by a characteristic dioxabicyclo[3.3.1]nonane platform formed by a double interflavan linkage. Potential bioactivities of these compounds are starting to be revealed, such as insulin-enhancing activity of 2 associated with diabetes remedy,[3] although detailed study has been hampered by the scarcity of natural products.
In addressing the chemical synthesis, the key challenge is the viability to construct the double interflavan linkages, where worth considering is the putative biogenesis of such double interflavan linkages.
We report herein the stereoselective syntheses of procyanidin A2 (1) and cinnamtannin B2 (2) based on the annulation strategy. Ethylenedioxy-bridged flavan units were prepared by DDQ oxidation of protected flavan units, which allowed dual activation at C2 and C4 position of the flavan unit, enabling annulation with nucleophilic units to construct double linked skeleton in regio- and stereoselective manner.
