Thin-layer chromatography of biflavonyls on silica gel : Structure—chromatographic behaviour correlations

Abstract

The chromatographic behaviour of 28 biflavonyls, including partially and fully methylated ethers, has been examined in five solvent systems. Benzene—pyridine—formic acid (36:9:5) has been found to be the most satisfactory developing system both for identification and separation of the biflavonyls and their methyl ethers while benzene—pyridine—ethyl formate—dioxan (5:1:2:2) has been claimed best for fully methylated biflavonyls. Both solvent systems have been used for the first successful separation of biflavonyls and their methyl ethers by preparative thin-layer chromatography. Relative R F values coupled with variations in the shades of the spots developed by spraying with diazotised sulphanilic acid may be used for ascertaining, approximately, the extent of the methylation in partial methyl ethers of the same series. The characteristics shades of fully methylated biflavonyls in UV light have been found to provide a means for their quick and satisfactory identification. An attempt has been made to correlate the structure of biflavonyls and their methyl ethers with their chromatographic behaviour. Isomeric pairs of fully methylated biflavonyls involving different interflavonyl linkages, such as hinokiflavone (C4′OC8″, C4′OC6″), amentoflavone (C3′C8″, C3′C6″), cupressuflavone (C8C8″) and agathisflavone (C6C8″) have easily been distinguished and oriented.