Isolation by high-pressure liquid chromatography of cis-trans isomers of β-apo-12'-carotenal and determination of their configurations by 1H NMR spectroscopy

Article abstract of DOI:10.1016/0584-8539(95)01525-Y

High pressure liquid chromatography of an isomeric mixture of β-apo-12'-carotenal, which was obtained by iodine-sensitized photo-isomerization, resolved eleven peaks of cis-trans isomers.The configurations of eight isomers, i.e., all-trans, 9-, 13-, 15-, 13'-mono-cis, and 9,13-, 9,13'- and 13,13'-di-cis, were determined by 1H NMR spectroscopy. 1H,1H COSY and long-range 1H,1H COSY spectra was used for the assignments of all the 1H signals.The isomerization shifts of the olefinic 1H signals and the NOE correlations, which were idenfied in the 1H,1H NOESY spectra, were used for the configurational determinations.In relation to the difference in isomeric composition between retinoids and carotenoids, the cis configurations found in the present compound (C25 aldehyde) are compared with those found in retinal (C20 aldehyde) and β-apo-8'-carotenal (C30 aldehyde) having a shorter and a longer conjugated chain, respectively.