Synthesis and Biological Evaluation of Phosphonate Analogues of 1 $\alpha$, 25-Dihydroxyvitamin $D_3$

A new series of phosphonate side chain analogues of 1$\alpha$,25-dihydroxyvitamin $D_3$ (1) have been synthesized. Antiproliferative activities of theses analogues (8a,b and 9a,b) using human keratinocyte cell shows that analogues which have natural A-ring show higher activity than unnatural A-ring series and almost equally active to 1 $\alpha$,25-Dihydroxyvitamin $D_3$(1) at 1 $\mu$M level.