On the side chain conformation of 1α,25-dihydroxyvitamin D3 responsible for binding to the receptor

Side chain mobility of 1,25(OH)2D3(1) and its 20-epimer (2) was analyzed and shown in a three-dimensional dot map that indicates the two distinct spatial regions accessible by the terminal 25-hydroxyl group for each vitamin. The biological activities of two analogs (3 and 4) of 1, which possess restricted side chain flexibility, were tested and the results suggest the spatial region of 1 responsible for binding to VDR and DBP.