Condensed tannins. 11. Isolation of a condensed tannin from black-wattle heartwood, and synthesis of (±)-7:3′:4′-trihydroxyflavan-4-ol

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Abstract
An optically active condensed tannin has been isolated from the heartwood of black wattle. The tannin resembles the accompanying (+)-7:3'':4''-trihydroxy-flavan-3:4-diol in most chemical and physical properties, but is trimeric on a C15 basis. Evidence available suggests that the tannin is a polymer of 7:3'':4''-trihydroxyflavan-3:4-diol condensed possibly through the heterocyclic ring system. ([plus or minus])-7:3'':4''-Trihydroxyflavan-4-ol has been synthesized from ([plus or minus])-butin by catalytic hydrogenation. The sterochemical significance of the reduction is discussed. The properties of the flavan-4-ol in comparison with those of the flavan-3-ol suggest that the hydroxyl group in position 4 might be involved in the biochemical condensation of flavan-3:4-diols, and also in the redness developed in these compounds and in associated or related condensed tannins.