ISOLATION AND STRUCTURAL ELUCIDATION OF THE PREDOMINANT GEOMETRICAL-ISOMERS OF ALPHA-CAROTENE

The recent development and application of a polymeric C-30 stationary phase have given unique separations of cis-trans carotenoid isomers in reversed-phase (RP) liquid chromatography (LC) owing to the exception al shape selectivity of this stationary phase. In the present research , several geometrical isomers of alpha-carotene were at least partiall y resolved from a photo-isomerized mixture when chromatographed on a 3 -mu m polymeric C-30 column. Double bond configurations of the five pr edominant cu-carotene peaks, as isolated on a semi-preparative C-30 co lumn, were unambiguously assigned using H-1 nuclear magnetic resonance (NMR) spectroscopy, giving the following order of elution: 13-cis, 13 '-cis, all-trans, 9-cis, and 9'-cis geometrical forms. Electronic abso rption spectra for these isomers were in agreement with the identifica tion of peaks. The alpha-carotene isomers separated and identified her ein had not been previously resolved in RPLC. Confirmation of the stru ctures of geometrical alpha-carotene isomers will aid further studies on the possible physiological roles of these compounds in biological t issues.