Novel flavan-3,4-diols from Acacia cultriformis
Flavan-3,3′,4,4′,7-pentaols (mollisacacidins) of (2R,3S,4R)- and (2R,3S,4S)-configurations are common to the heartwoods of a number of authentic samples of Acacia cultriformis. These are accompanied in some instances by a stereochemically analogous pair of flavan-3,4,4′,7-tetraols (guibourtacacidins) and the 8-O-methyl derivatives of (2R,3S,4R)-flavan-3,4,4′,7,8-pentaol (teracacidins) and (2R,3S,4S)-flavan-3,3′,4,4′,7,8-hexaol (melacacidins). This represents the first isolation of methyl ethers of natural flavan-3,4-diols.
Complete analysis of the n.m.r. spectra of their methyl ethers and methyl ether diacetates enables comparison of the chemical shifts of benzenoid protons for the first time.