All-E-(3R,6'R)-3-hydroxy-3',4'-didehydro-beta,gamma-carotene (
anhydrolutein I) and all-E-(3R,6'R)-3-hydroxy-2',3'-didehydro-beta,epsilon-carotene (2',3'-anhydrolutein II) have been isolated and characterized from extracts of human plasma using semipreparative high-performance liquid chromatography (HPLC) on a C18 reversed-phase column. The identification of anhydroluteins was accomplished by comparison of the UV-Vis absorption and mass spectral data as well as HPLC-UV-Vis-mass spectrometry (MS) spiking experiments using fully characterized synthetic compounds. Partial synthesis of anhydroluteins from the reaction of
lutein with 2% H2SO4 in
acetone, in addition to
anhydrolutein I (54%) and 2',3'-anhydrolutein II (19%), also gave (3'R)-3'-hydroxy-3,4-dehydro-beta-carotene (3',4'-anhydrolutein III, 19%). While
anhydrolutein I has been shown to be usually accompanied by minute quantities of 2',3'-anhydrolutein II (ca. 7-10%) in human plasma, 3',4'-anhydrolutein III has not been detected. The presence of
anhydrolutein I and II in human plasma is postulated to be due to
acid catalyzed
dehydration of the dietary
lutein as it passes through the stomach. These anhydroluteins have also been prepared by conversion of
lutein diacetate to the corresponding anhydrolutein
acetates followed by alkaline hydrolysis. However, under identical acidic conditions, loss of
acetic acid from
lutein diacetate proceeded at a much slower rate than
dehydration of
lutein. The structures of the synthetic anhydroluteins, including their absolute configuration at C(3) and C(6') have been unambiguously established by 1H NMR and in part by 13C NMR, and circular dichroism.