Removal of the 26-methyl group from 19-nor-1α,25-dihydroxyvitamin D₃ markedly reduces in vivo calcemic activity without altering in vitro VDR binding, HL-60 cell differentiation, and transcription.

Twelve new analogues of 19-nor-1α,25-dihydroxyvitamin D₃ (5-16) were prepared by convergent syntheses, employing the Wittig-Horner reaction. The necessary Grundmann type ketones (45-48), possessing fixed configurations of the hydroxyl group at C-25, were obtained by a multistep procedure from commercial vitamin D₂ and enantiomers of 1,3-butanediol (23 and 24). We have examined the influence of removal of one of the methyl groups located at C-25 on the biological in vitro and in vivo activity. The in vivo tests showed that the synthesized vitamin D compounds (5-16) exhibit reduced calcemic activity both in bone and in the intestine. However, in vitro potency of 2-methylene and 2α-methyl compounds (5-10, 13, and 14) remained similar or enhanced as compared to that of 1α,25-(OH)₂D₃.