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

Abstract

Thermal and iodine-catalyzed photochemical ( Z/ E)-isomerization of deoxylutein II [(3 R,6′ R)-3-hydroxy-3′,4′-didehydro-β,γ-carotene, anhydrolutein I] ( 2), the dehydration product of lutein [(3 R,3′ R,6′ R)-β,ɛ-carotene-3,3′-diol] ( 4), yielded multi-component mixtures of ( Z)-isomers. By I 2-catalyzed photoisomerization, (9 Z)- 2, (9′ Z)- 2, (13 Z)- 2, (13′ Z)- 2 and (15 Z)- 2 are generated as main products. In addition, this thermodynamic-equilibrium mixture contains traces of (9 Z,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-d 6/D 2O = 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.