Add time:07/18/2019         Source:sciencedirect.com

Gas chromatography/mass spectrometric (GC/MS) analysis of 24R,25-dihydroxyvitamin D3 (24,25-(OH)2D3, 1a) in rat serum is examined using 6,19,19-trideuterated derivative (24,25-(OH)2[6,19,19-2H]D3, 1c) as an internal standard. Pyro- and isopyro-24,25-(OH)2D3 (2a and 3a) are synthesized and the structures are determined unambiguously by their spectral data including nuclear overhauser enhancement study of the NMR spectra. The two peaks which appear on the total ion chromatogram of 24,25-cyclic n-butyl boronate-3-trimethylsilyl derivative of 24,25-(OH)2D3 are identified to be those of the pyro and isopyro isomers (2a and 3a) by direct comparison with the synthetic standards. Analysis of the GC/MS spectrum of 24,25-(OH)2[6,19,19-2H]D3 (1c) indicated that the CH3(19) is preferentially eliminated in the fragmentation giving rise to a base peak (M-TMSOH-Me)+. Thus the molecular ion peak, which is about 20% of the base peak, rather than the base peak is used for GC/MS assay of 24,25-(OH)2D3 in serum.

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