Increased intake of lutein from vegetables promotes increased density of the macular pigment and therefore may protect against age-related macular degeneration. Our objective was to use a 13C tracer and high-precision gas chromatography-combustion interfaced-isotope ratio mass spectrometry (GC-C-IRMS) to investigate metabolism of a lutein dose equivalent to that absorbed from vegetables. Biosynthetic per-labeled (>99% 13C) lutein was purified from a commercially available extract of algal biomass. Subjects (n = 4) ingested 3 mg of [13C]lutein with a standardized low-carotenoid breakfast. Blood samples were collected at baseline and then hourly for 12 h; additional blood samples were drawn at 16, 24, 48, 72, 96, 192, 360, and 528 h. To produce perhydro-beta-carotene suitable for analysis by GC-C-IRMS, the plasma lutein fraction was hydrogenated on palladium-on-carbon catalyst with acid-catalyzed hydrogenolysis. The stable carbon isotope (13C/12C) ratio measured by GC-C-IRMS was used to calculate the plasma concentration of [13C]lutein. There was a rapid increase in [13C]lutein in plasma until peak enrichment at 16 h followed by a decline to the next measurement at 24 h. At 528 h, small changes in 13C enrichment from baseline could still be measured in plasma lutein. High-precision GC-C-IRMS enables complete definition of the appearance and disappearance of [13C]lutein in plasma after ingestion of a dose similar to that absorbed from foods.

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Substituted phenylacetic acids are readily decarboxylated when treated with ceric ammonium nitrate in aqueous acetonitrile solutions containing nitric acid to give carbon dioxide and the corresponding benzyl alcohol, benzaldehyde, and benzyl nitrate. Oxygen-trapping experiments indicate that benzyl radicals are formed as intermediates. A Hammett plot of the relative rates of oxidation of meta-and para-substituted phenylacetic acids vs. + values gave a p of -2.91 ± 0.29. The oxidative decarboxylation is proposed to be a one-electron process with the rate-determining step being the decomposition of a carboxylic acid-cerium(IV) complex to a benzyl radical and carbon dioxide through a very polar transition state.The oxidative decarboxylation of carboxylic acids has been studied extensively. Many of the oxidants used for this reaction are metallic ones such as lead(IV),2 cobalt(III),3 silver(II),4 manganese(III),5 thallium(III),6 and chromic acid,7 but nonmetallic oxidants8 have also been used. In addition, oxidative decarboxylations have been effected electrolytically.9

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