High-performance liquid chromatography of aryltet-rahydronaphthalene lignans

Abstract The retention behaviour of some aryltetrahydronaphthalene lignans is studied. Adsorption chromatography on silica eluted with n -heptane dichloromethane-meth- anol (90:10:4) and reversed-phase chromatography on a C C18 column with methanol- water (45:55) as mobile phase are effective for the resolution of the seven known diastereoisomers of podophyllotoxin. Methanol is essential for the separation of the diastereoisomers by reversed-phase chromatography, but is less useful for the separation of the functional-group derivatives of podophyllotoxin. Acetonitrile and/or di-methyl sulphoxide are superior for the resolution of functional derivatives, but are unable to separate the diastereoisomers. A ternary mobile phase of acetonitrile- methanol -water (22.5:22.5:55), dimethyl sulphoxide-methanol-water (10:25:35) or a quaternary solvent mixture of acetonitrile-dimethyl sulphoxide-methanol-water (20:20:10:50) is required for the separation of a mixture containing diastereoisomers and functional-group derivatives. The relative retention of the lignans can be explained by the relative ability of a lignan to interact with the adsorption site or by its relative hydrophobicity in reversed-phase chromatography.