Tannins and Related Compounds. CVI. Preparation of Aminoalditol Derivatives of Hydrolyzable Tannins Having α-and β-Glucopyranose Cores, and Its Application to the Structure Elucidation of New Tannins, Reginins A and B and Flosin A, Isolated from Lagerstro

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To avoid tautomerism in the hydrolyzable tannins which lack an acyl group at the glucose C-1 position, a new method for the protection fo the C-1 atom has been developed. That is reaction of the tannins with p-anisidine in the presence of acetic acid, followed by sodium cyanoborohydride reduction, afforded, without notable hydrolysis of ester bonds, the aminoalditol derivatives (1a-7a) in 50-80% yields. The proton and carbon-13 nuclear magnetic resonance (^1H-and ^<13>C-NMR) spectra of these derivatives exhibited much simpler signal patterns typical of an open-chain form of glucose, and almost all the singals could be assigned.Application of this method to the structure elucidation of the new tannins, flosin A (22) and reginins A (23) and B (24), isolated from the leaves of Lagerstroemia flos-reginae RETZ. (Lythraceae), established their structures including the orientation of the 4,6-positioned valoneoyl group. In addition, the structure of a new hydrolyzable tannin, lagerstroemin (21), which was concomitantly isolated from the above species, was elucidated.
社団法人日本薬学会の論文
1991-03-25