Structure elucidation of deoxylutein II isomers by on-line capillary high performance liquid chromatography–1H nuclear magnetic resonance spectroscopy

Thermal and iodine-catalyzed photochemical (Z/E)-isomerization of deoxylutein II [(3R,6′R)-3-hydroxy-3′,4′-didehydro-β,γ-carotene, anhydrolutein I] (2), the dehydration product of lutein [(3R,3′R,6′R)-β,ɛ-carotene-3,3′-diol] (4), yielded multi-component mixtures of (Z)-isomers. By I2-catalyzed photoisomerization, (9Z)-2, (9′Z)-2, (13Z)-2, (13′Z)-2 and (15Z)-2 are generated as main products. In addition, this thermodynamic-equilibrium mixture contains traces of (9Z,9′Z)-2 and other (di-Z)-isomers in minor concentrations. Thirteen isomers are chromatographically separated and detected on-line by UV–vis and mass spectrometry. (all-E)-Deoxylutein II (2) and six of its (Z)-configured isomers are separated by capillary HPLC (acetone-d6/D2O = 85:15) and detected on-line by 1H NMR spectroscopy in a microprobe. With the microprobe and the active detection volume of 1.5 μl, it is possible to perform structure elucidation with very small amounts available for various (Z)-isomers of deoxylutein II (2) in the isomerization mixture.