Countercurrent chromatography (CCC) was used for the enrichment of α-tocodienol (α-T2), a rare vitamin E-related minor compound previously tentatively detected in palm oil. Hitherto, only one isomer has been mentioned to occur at traces in palm oil. However, CCC fractionation followed by GC/MS measurements of all fractions resulted in the detection of two α-T2 isomers in five different palm oil vitamin E dietary supplement capsules. Five repetitive CCC separations of ~ 1 g sample and additional purification steps by column chromatography provided ~ 2 mg of two equally abundant α-T2 isomers with a purity of ~ 85%. The positions of the double bonds in the alkyl side chain could be assigned by means of two characteristic chemical shifts in the 1H NMR spectrum. Accordingly, the structures of the α-T2 isomers were 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridec-3,11-dienyl)chroman-6-ol (double bonds in 3',11'-position) and 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridec-7,11-dienyl)chroman-6-ol (double bonds in 7',11'-position). Natural occurrence of both isomers was proven by GC/MS screening of crude palm oil after saponification and CCC separation. Moreover, GC/MS analysis allowed the tentative assignment of γ-tocomonoenol (γ-T1) and β-tocomonoenol (β-T1) as trace compounds in palm oil.
Keywords: Countercurrent chromatography; NMR spectroscopy; Palm oil; Vitamin E; α-Tocodienol isomers.