Synthesis of vitamin D₃ and calcitriol dimers as potential chemical inducers of vitamin D receptor dimerization.

The design and synthesis of vitamin D₃ dimers and 1a,25-dihydroxyvitamin D₃ (calcitriol) dimers are described. The dimers were designed with a view to doubly binding the vitamin D receptor (VDR) and inducing the receptor homodimerization. In the dimers the units are linked through the C-11 position in ring C by an alkyl side chain of six or 10 carbon atoms, far from the hydroxy groups responsible for the VDR binding. The linker is formed by olefin metathesis of an olefinic side chain at the C-11 position introduced by stereoselective cuprate addition. The synthesis, which is both short and convergent, uses the Wittig-Horner approach to construct the vitamin D triene system and allows the preparation of dimers with a linker of modulated length with the purpose of optimizing the vitamin D₃-VDR interaction.