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

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Abstract
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[image],7,8-trihydroxyl pattern. These were resolved by preparative paper chromatography and preparative paper ionophore-sis. Crystalline ([long dash])-teracacidine [(2R,3R,4R)-4[image],7,8-trihydroxy-2,3-cis-flavan-3,4-cis-diol] was obtained in high (10%) yield, and a new crystalline derivative of ([long dash])-isoteracacidin[([long dash])-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. The absolute configurations of ([long dash])-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 ([long dash])-teracacidin. Possible reasons for the absence of polymeric leuco-anthocyanidin tannins are discussed. (+)-4[image],7,8-Trihydroxy-dihydroflavonol and (+)-4[image]7,8-trihydroxyflavanone were isolated for the first time. 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.