Synthesis and binding-analysis of 5E-[19-(2-bromoacetoxy)methyl]25-hydroxyvitamin D3 and 5E-25-hydroxyvitamin D3-19-methyl[(4-azido-2-nitro)phenyl]glycinate:: Novel C19-modified affinity and photoaffinity analogs of 25-hydroxyvitamin D3

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 in 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 it 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. (C) 1998 by Elsevier Science Inc.