Isolation and structural elucidation of the geometrical isomers of lutein and zeaxanthin in extracts from human plasma

Abstract

All-E-(3R,3'R,6'R)-lutein, all-E-(3R,3'R)-zeaxanthin, all-E-(3R,3'S,6'R)-3'-epilutein and some geometrical isomers of the former two dihydroxycarotenoids have been separated from an extract of human plasma by semipreparative high-performance liquid chromatography on a silica-based nitrile-bonded column. In the order of chromatographic elution, the isolated fractions were identified as all-E-lutein, all-E-zeaxanthin, all-E-3'-epilutein, 9Z-lutein, 9'Z-lutein, a mixture of 13Z-lutein and 13'Z-lutein, 9Z-zeaxanthin, 13Z-zeaxanthin and 15Z-zeaxanthin. The structures of all compounds, including the relative configuration at C(3') and C(6') of the luteins and the position of the stereomutated double bonds in the geometrical isomers, were unambiguously established by 1H nuclear magnetic resonance spectroscopy. The absolute configuration of the three all-E compounds was derived by circular dichroism and is also assumed to be valid for the geometrical isomers. The ultraviolet-visible absorption and mass spectra of each of the individually isolated compounds were also in agreement with the proposed structures.