Chemical Synthesis and Biological Activities of 20S,24S/R‑Dihydroxyvitamin D3 Epimers and Their 1α-Hydroxyl Derivatives

Bioactive vitamin D3 metabolites 20S,24S-dihydroxyvitamin D3 [20S,24S(OH)2D3] and 20S,24R-dihydroxyvitamin D3 [20S,24R­(OH)2D3] were chemically synthesized and confirmed to be identical to their enzymatically generated counterparts. The absolute configurations at C24 and its influence on the kinetics of 1α-hydroxylation by CYP27B1 were determined. Their corresponding 1α-hydroxyl derivatives were subsequently produced. Biological comparisons of these products showed different properties with respect to vitamin D3 receptor activation, anti-inflammatory activity, and antiproliferative activity, with 1α,20S,24R­(OH)2D3 being the most potent compound.