A short practical approach to 24R,25-dihydroxyvitamin D3

Stereoselective Synthesis of 24-Fluoro-25-Hydroxyvitamin D3 Analogues and Their Stability to hCYP24A1-Dependent Catabolism

Two 24-fluoro-25-hydroxyvitamin D₃ analogues (3,4) were synthesized in a convergent manner. The introduction of a stereocenter to the vitamin D₃ side-chain C24 position was achieved via Sharpless dihydroxylation, and a deoxyfluorination reaction was utilized for the fluorination step. Comparison between (24R)- and (24S)-24-fluoro-25-hydroxyvitamin D₃ revealed that the C24-R-configuration isomer 4 was more resistant to CYP24A1-dependent metabolism than its 24S-isomer 3. The new synthetic route of the CYP24A1 main metabolite (24R)-24,25-dihydroxyvitamin D₃ (6) and its 24S-isomer (5) was also studied using synthetic intermediates (30,31) in parallel.

Introduction of fluorine atoms to vitamin D3 side-chain and synthesis of 24,24-difluoro-25-hydroxyvitamin D3

During our ongoing studies of vitamin D, we focused on the vitamin D₃ side-chain 24-position, which is the major metabolic site of human CYP24A1. In order to inhibit the metabolism of vitamin D₃, 24,24-difluorovitamin D₃analogues are important candidates. In this paper, we report the practical introduction of the difluoro-unit to the 24-position to synthesize 24,24-difluoro-CD ring (1) and 24,24-difluoro-25-hydroxyvitamin D₃ (2).

Clinical utility of simultaneous quantitation of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D by LC-MS/MS involving derivatization with DMEQ-TAD

CONTEXT

The discovery of hypercalcemic diseases due to loss-of-function mutations in 25-hydroxyvitamin D-24-hydroxylase has placed a new demand for sensitive and precise assays for 24,25-dihydroxyvitamin D [24,25-(OH)2D].

OBJECTIVE

We describe a novel liquid chromatography and tandem mass spectrometry-based method involving derivatization with DMEQ-TAD {4-[2-(6,7-dimethoxy-4-methyl-3,4-dihydroquinoxalinyl)ethyl]-1,2,4-triazoline-3,5-dione} to simultaneously assay multiple vitamin D metabolites including 25-hydroxyvitamin D (25-OH-D) and 24,25-(OH)2D using 100 μL of serum with a 5-minute run time.

DESIGN

The assay uses a newly synthesized internal standard d6-24,25-(OH)2D3 enabling the quantitation of 24,25-(OH)2D3 as well as the determination of the ratio of 25-OH-D3 to 24,25-(OH)2D3, a physiologically useful parameter.

SETTING

We report data on more than 1000 normal and disease samples involving vitamin D deficiency or hypercalcemia in addition to studies involving knockout mouse models.

RESULTS

The assay showed good correlation with samples from quality assurance schemes for 25-OH-D (25-OH-D2 and 25-OH-D3) determination (-2% to -5% bias) and exhibited low inter- and intraassay coefficients of variation (4%-7%) and lower limits of quantitation of 0.25-0.45 nmol/L. In clinical studies, we found a strong correlation between serum levels of 25-OH-D3 and 24,25-(OH)2D3 (r(2) = 0.80) in subjects over a broad range of 25-OH-D3 values and a marked lack of production of 24,25-(OH)2D3 below 25 nmol/L of 25-OH-D. The ratio of 25-OH-D3 to 24,25-(OH)2D3, which remained less than 25 in vitamin D-sufficient subjects (serum 25-OH-D < 50 nmol/L) but was greatly elevated (80-100) in patients with idiopathic infantile hypercalcemia.

CONCLUSIONS

The new method showed good utility in clinical settings involving vitamin D deficiency; supplementation with vitamin D and idiopathic infantile hypercalcemia, as well as in animal models with ablation of selected cytochrome P450-containing enzymes involved in vitamin D metabolism.