The synthesis and biological activity of 25-hydroxy-26,27-dimethylvitamin D 3 and 1,25-dihydroxy-26,27-dimethylvitamin D 3: highly potent novel analogs of vitamin D 3

Abstract

We synthesized 25-hydroxy-26,27-dimethylvitamin D 3, 9, and 1,25-dihydroxy-26,27-dimethylvitamin D 3,14, from chol-5-enic acid-3β-ol and tested their biological activity in vivo and in vitro. 9 was found to be a highly potent vitamin D analog with bioactivity similar to that of 25-hydroxyvitamin D 3. 9 bound to rat plasma vitamin D binding protein with approximately one-third the affinity of 25-hydroxyvitamin D 3. In a duodenal organ culture system and in a competitive binding assay with chick intestinal 1,25-dihydroxyvitamin D receptor, 9 was significantly more potent than 25-hydroxyvitamin D 3. 1,25-Dihydroxy-26,27-dimethylvitamin D 3, 14 was also highly active in vivo. At doses of 1000–5000 pmol/rat, its action was more sustained than that of 1,25-dihydroxyvitamin D 3.14 bound to vitamin 0 binding protein about 18 times less effectively than 1,25-dihydroxyvitamin D 3. 14 bound to the chick intestinal cytosol receptor with an affinity one-half that of 1,25-dihydroxyvitamin D 3. In a duodenal organ culture system, 14 was about half as active as 1,25-dihydroxyvitamin D 3. Extension of the sterol side chain, at C-26 and C-27, by methylene groups, prolongs the bioactivity of a vitamin D sterol hydroxylated at C-1 and C-25; the corresponding sterol, hydroxylated only at C-25, does not show any alteration of its bioactivity in vivo. These newly synthesized analogs may potentially be of therapeutic use in various mineral disorders.