Synthesis of (22R)- and (22S)-22,25-Dihydroxyvitamin D3 and determination of their biological activity

Synthesis and biological activity of 22-iodo- and (E)-20(22)-dehydro analogues of 1alpha,25-dihydroxyvitamin D3

Construction of 25-hydroxy-steroidal side chain substituted with iodine at C-22 was elaborated on a model PTAD-protected steroidal 5,7-diene and applied to a synthesis of (22R)- and (22S)-22-iodo-1alpha,25-dihydroxyvitamin D3. Configuration at C-22 in the iodinated vitamins, obtained by nucleophilic substitution of the corresponding 22S-tosylates with sodium iodide, was determined by comparison of their iodine-displacement processes and cyclizations leading to isomeric five-membered (22,25)-epoxy-1alpha-hydroxyvitamin D3 compounds. Also, 20(22)-dehydrosteroids have been obtained and their structures established by 1H NMR spectroscopy. When compared to the natural hormone, (E)-20(22)-dehydro-1alpha,25-dihydroxyvitamin D3 was found 4 times less potent in binding to the porcine intestinal vitamin D receptor (VDR) and 2 times less effective in differentiation of HL-60 cells. 22-Iodinated vitamin D analogues showed somewhat lower in vitro activity, whereas (22,25)-epoxy analogues were inactive. Interestingly, it was established that (22S)-22-iodo-1alpha,25-dihydroxyvitamin D3 was 3 times more potent than its (22R)-isomer in binding to VDR and four times more effective in HL-60 cell differentiation assay. The restricted mobility of the side chain of both 22-iodinated vitamin D compounds was analyzed by a systematic conformational search indicating different spatial regions occupied by their 25-oxygen atoms. Preliminary data on the in vivo calcemic activity of the synthesized vitamin D analogues indicate that (E)-20(22)-dehydro-1alpha,25-dihydroxyvitamin D3 and 22-iodo-1alpha,25-dihydroxyvitamin D3 isomers were ca. ten times less potent than the natural hormone 1alpha,25-(OH)2D3 both in intestinal calcium transport and bone calcium mobilization.

Synthesis and biological activity of vitamin D3 analogues

Many analogues of vitamin D metabolites including stereochemical isomers and fluorine substituents were synthesized, and their biological activities were determined by in vitro and in vivo assays. Among those analogues, 24,24-F2-1,25-(OH)2D3 and 26,26,26,27,27,27-F6-1,25-(OH)2D3 are more active than the most potent naturally occurring vitamin D3 metabolite, 1,25-(OH)2D3.