A new flavan-3,4-diol from Acacia auriculiformis by paper ionophoresis

1. The heartwood of A. auriculiformis contains a typical mixture of analogues consisting of three isomeric flavan-3,4-diols, a dihydroflavonol, flavanone, flavonol and chalcone based on the 4′,7,8-trihydroxyl pattern. These were resolved by preparative paper chromatography and preparative paper ionophoresis. 2. Crystalline (−)-teracacidin [(2R,3R,4R)-4′,7,8-trihydroxy-2,3-cis-flavan-3,4-cis-diol] was obtained in high (10%) yield, and a new crystalline derivative of (−)-isoteracacidin [(−)-2,3-cis-3,4-trans isomer] was isolated. The crystalline methyl ether of a new (+)-2,3-trans-3,4-cis isomer was isolated. 3. The absolute configurations of (−)-isoteracacidin (2R,3R,4S) and of the (+)-2,3-trans-3,4-cis isomer (2R,3S,4S) were tentatively assigned on the basis of nuclear-magnetic-resonance spectroscopy, paper ionophoresis and paper-chromatographic comparison with the epimerization products of (−)-teracacidin. 4. Possible reasons for the absence of polymeric leuco-anthocyanidin tannins are discussed. 5. (±)-4′,7,8-Trihydroxydihydroflavonol and (±)-4′,7,8-trihydroxyflavanone were isolated for the first time. 6. The bark polyphenols consist mainly of polymeric leuco-delphinidins and leuco-cyanidins which redden exceptionally rapidly to light. The mechanism of this phenomenon is discussed.