Methyl substitution of the 25-hydroxy group on 2-methylene-19-nor-1alpha,25-dihydroxyvitamin D3 (2MD) reduces potency but allows bone selectivity.

The discovery of 2-methylene-19-nor-1alpha,25-dihydroxyvitamin D3 (2MD) as a bone selective and bone anabolic form of vitamin D has stimulated an investigation of structure/function of bone selectivity. Four new 2-substituted-19-norvitamin D analogs 3-6 have been developed to study the structure-activity relationship at C-25. As predicted, removing the 25-hydroxy group (compound 3) from the very potent analog 2MD and its 2-methyl derivatives (5 and 6) dramatically reduces in vitro activities, but biological potency is nearly fully restored in vivo likely due to in vivo 25-hydroxylation. The introduction of a methyl group at C-25 (compound 4) that blocks in vivo 25-hydroxylation reduces biological activity both in vitro and in vivo. However, analog 4 retains bone selectivity making it interesting as a possible therapeutic for bone loss diseases.