Synthesis and biological activity of novel vitamin D analogs: 24,24-difluoro-25-hydroxy-26,27-dimethylvitamin D3 and 24,24-difluoro-1α,25-dihydroxy-26,27-dimethylvitamin D3

We synthesized 24,24-difluoro-25-hydroxy-26,27-dimethylvitamin D₃(16), and 24,24-difluoro-1α,25-dihydroxy-26,27-dimethylvitamin D₃(21), from 3/β-hydroxy-22,23-dinorcholenic acid 3-acetate. Compound 16 was found to be a highly potent vitamin D analogue with bioactivity similar to that of 25-hydroxyvitamin D₃in vivo. Compound 16 was bound by vitamin D binding protein with an affinity slightly less than that of 25-hydroxyvitamin D₃. It was bound to the intestinal cytosol receptor for 1,25-dihydroxyvitamin D₃with approximately the same affinity as that of 25-hydroxyvitamin D₃. In the organ-culture duodenum, 16 induced the synthesis of calcium binding protein with a potency approximately 1/20 that of 1,25-dihydroxyvitamin D₃. Compound 21 was also noted to be a highly potent vitamin D analogue with bioactivity in vivo similar to that of 1,25-dihydroxyvitamin D_3.It was bound to vitamin D binding protein with an affinity considerably less than that of 1,25-dihydroxyvitamin D₃. It was bound to the intestinal cytosol receptor for 1,25-dihydroxyvitamin D₃with an affinity slightly iess than that of the native hormone. In the organ-culture duodenum, 21 was noted to be about 3 times more active than 1,25-dihydroxyvitamin D3 in the induction of calcium binding protein. The introduction of fluorines at C-24 and extension of the sterol side chain at C-26 and C-27 by methylene groups results in vitamin D analogues that have biological activity in vivo similar to those of the respective nonfluorinated natural sterols.