Simultaneous measurement of plasma vitamin D(3) metabolites, including 4ß,25-dihydroxyvitamin D(3), using liquid chromatography-tandem mass spectrometry.

Simultaneous and accurate measurement of circulating vitamin D metabolites is critical to studies of the metabolic regulation of vitamin D and its impact on health and disease. To that end, we have developed a specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method that permits the quantification of major circulating vitamin D(3) metabolites in human plasma. Plasma samples were subjected to a protein precipitation, liquid-liquid extraction, and Diels-Alder derivatization procedure prior to LC-MS/MS analysis. Importantly, in all human plasma samples tested, we identified a significant dihydroxyvitamin D(3) peak that could potentially interfere with the determination of 1α,25-dihydroxyvitamin D(3) [1α,25(OH)(2)D(3)] concentrations. This interfering metabolite has been identified as 4ß,25-dihydroxyvitamin D(3) [4ß,25(OH)(2)D(3)] and was found at concentrations comparable to 1α,25(OH)(2)D(3). Quantification of 1α,25(OH)(2)D(3) in plasma required complete chromatographic separation of 1α,25(OH)(2)D(3) from 4ß,25(OH)(2)D(3). An assay incorporating this feature was used to simultaneously determine the plasma concentrations of 25OHD(3), 24R,25(OH)(2)D(3), 1α,25(OH)(2)D(3), and 4ß,25(OH)(2)D(3) in healthy individuals. The LC-MS/MS method developed and described here could result in considerable improvement in quantifying 1α,25(OH)(2)D(3) as well as monitoring the newly identified circulating metabolite, 4ß,25(OH)(2)D(3).

Stereoselective convergent synthesis of 24,25-dihydroxyvitamin D3 metabolites: a practical approach.

Vitamin D3 active metabolites 24R,25-(OH)2-D3, 24S,25-(OH)2-D3, and 1 alpha, 24R,25-(OH)3-D3 were synthesized by a convergent and stereoselective approach. In the synthetic route, the stereogenic center at C-24 was generated through ultrasonically induced aqueous conjugate addition of iodide 6 to Seebach's dioxolanone 5, and the vitamin D triene system was constructed using the Lythgoe approach. The synthesis, which is both short (seven steps from iodide 6) and efficient (32-40% overall yield), allows the preparation of large quantities of the metabolites and provides a novel example of a highly stereoselective reaction promoted by the zinc-copper couple in aqueous media.