Synthesis and Binding-analysis of 5E-[19-(2-bromoacetoxy)methyl]25-hydroxyvitamin D 3 and 5E-25-hydroxyvitamin D 3-19-methyl[(4-azido-2-nitro)phenyl]glycinate: Novel C 19-modified Affinity and Photoaffinity Analogs of 25-hydroxyvitamin D 3

Abstract

Synthesis of novel C 19-modified affinity and photoaffinity analogs of vitamin D 3 and 25-hydroxyvitamin D 3(25-OH-D 3) is described. A key step in the synthesis is a Horner–Emmons reaction between C 19-nor-cyclovitamin D 3-C 19-ketone or C 19-nor-25-hydroxy-cyclovitamin D 3-C 19-ketone and diethyl cyanomethylphosphonate. Competitive radioligand binding assays with human serum vitamin D-binding protein (DBP) and 5E-[19-(2-bromoacetoxy)methyl]25-hydroxyvitamin D 3 and 5E-25-hydroxyvitamin D 3-19-methyl[(4-azido-2-nitro)phenyl]glycinate, 25-OH-D 3-analogs containing affinity and photoaffinity probes at C 19-position, demonstrated that these compounds displaced radiolabeled 25-OH-D 3 from the binding pocket of DBP in a dose-dependent manner. Thus, these affinity and photoaffinity analogs are potentially useful in determining the ligand binding site topographies of DBP and possibly the vitamin D receptor.