Synthesis and characterization of 20-hydroxyvitamin D3 with the A-ring modification

Abstract Two novel 20-hydroxyvitamin D 3 analogues ( 4a,b ) with the A-ring modification have been synthesized by a convergent manner. An alternative pathway of vitamin D 3 metabolism by cytochrome P450scc CYP11A1 was reported to afford 20-hydroxyvitamin D 3 ( 3 ), functions of which remain to be explored. Based on the structure of the 20-hydroxy metabolite, novel analogues ( 4a,b ) with the modifications, including the 1α-hydroxy, 25-hydroxy and 2α-methyl groups, have been designed. The side chain of the requisite CD-ring portions ( 9a,b ) was introduced by Grignard reaction as a key step, and the stereochemistry at the C20 position was confirmed by the X-ray crystal structure analysis of the synthetic intermediate ( 8b ). Preliminary biological characterization using the bovine thymus vitamin D receptor suggested that the introduction of the active motifs into the 20-hydroxyvitamin D 3 scaffold elevated the receptor affinity.