A proton magnetic resonance relaxation time study of several vitamin D derivatives

Abstract

PMR relaxation time studies at 200 and 400 MHz were measured for vitamins D2, D3 and the biologically active 1.alpha.,25-(OH)2D3. A comparison of these relaxation times at the 2 frequencies allows the evaluation of the dipolar correlation times for the different protons in the molecule. These are very short and range from < 0.7 .times. 10-10 to 1.2 .times. 10-10 s. Application of the Solomon equation to the relaxation times of the 19Z and 19E protons allows a calculation of the interuclear distance since these 2 geminal protons relax each other predominantly by the dipolar mechanism. Using the T1 values, the calculated distances are 1.98 .+-. 0.10 .ANG. for 1.alpha.,25-(OH)2D3, 2.01 .+-. 0.10 .ANG. for D3 and 1.95 .+-. 0.10 .ANG. for D2. The calculated distance based on a neutron diffraction distance for the C-H bond is 1.91 .ANG.. The measurement of the relaxation times also allows a definitive spectral assignment of the 21- and 28-methyl protons for vitamin D2.