Synthesis of 13C Labeled Vitamin D Metabolites for Their Use in LC-MS/MS: Valuable Tools for Cancer Research and Other Applications

Background/Aim: Simultaneous assessment of various vitamin D metabolites in human biofluids by liquid chromatography tandem mass spectrometry (LC-MS/MS) represents a new promising tool for the differential diagnosis of vitamin D-related diseases. Particularly, besides 25(OH)VD2/3, low-abundant medicinally relevant vitamin D metabolites, such as 24,25(OH)2VD2/3, 1,25(OH)2VD2/3, and 1,24,25(OH)3VD2/3, along with their 3-epi-derivatives have to be considered. Materials and Methods: The assessment of these metabolites by LC-MS/MS requires the development of calibration and reference standards, that is, their labeling with multiple deuterium-, or even better, 13C-atoms. Results: Overall, 10 13C-labeled vitamin D metabolites have been chemically synthesized and obtained in good yield and high purity. Conclusion: Access to a wide variety of 13C-labeled highly pure vitamin D metabolites enables the advancement of LC-MS/MS applications towards a better understanding of differential diagnosis of vitamin D-related diseases.