Vitamin D in Solution: Conformations of Vitamin D 3 , 1α,25-Dihydroxyvitamin D 3 , and Dihydrotachysterol 3

Abstract

Solution conformations of the A and seco B rings of vitamin D₃, 1_α, 25-dihydroxyvitamin D₃, 1_α-hydroxyvitamin D₃, and dihydrotachysterol₃ have been established by high resolution, 300-megahertz proton magnetic resonance spectroscopy. The A ring of these steroids is dynamically equilibrated between two chair conformers. For vitamin D₃, 1_α-hydroxyvitamin D₃, and 1_α,25-dihydroxyvitamin D₃ the relative proportions of the two conformers are 1 : 1, whereas dihydrotachysterol3 exists principally as only one conformer. Thus, the substituent groups on the A ring may be either equatorially or axially oriented, and suggests a refinement of the existing topological model for vitamin D hormonal activity.