Synthesis of vitamin D3 derivatives with nitrogen-linked substituents at A-ring C-2 and evaluation of their vitamin D receptor-mediated transcriptional activity

Abstract

Binding of a series of novel 1α,25-dihydroxyvitamin D₃ (1,25-VD₃) derivatives, having a nitrogen-linked substituent at the 2α- or 2β-position of the A-ring (2-N-substituted compounds), with the vitamin D receptor (VDR) was investigated by means of computational docking studies. Selected compounds were synthesized by coupling A-ring synthons 6 and/or 7 with CD-ring-bearing bromomethylene 5 under Trost's conditions. The 2α- and 2β-stereoisomers of the A-ring synthons were synthesized from L-serine (8) as a single chiral source by installing vinyl and propargyl groups at opposite ends of the molecule. The activity of the obtained compounds was evaluated by means of a luciferase-based VDR transcriptional activity assay in NIH3T3 cells. Relatively small substituents incorporating a hydrogen-bonding donor, i.e., NHAc and NHMs, were effective for eliciting VDR transcriptional activity, and 2β-NHMs-1,25-VD₃ (Xa) showed the highest activity, being more potent than 1,25-VD₃. Derivatives with bulky substituents were inactive. These new insights into the structure–activity relationships of 1,25-VD₃ derivatives may be helpful in separating the various biological activities of 1,25-VD₃ and in generating novel therapeutic drug candidates.