A proton magnetic resonance nuclear Overhauser enhancement study. Application to vitamin D derivatives D2 and D3

Abstract

Nuclear Overhauser effect [nOe] difference experiments on vitamins D2 and D3 at 400 MHz allow an unambiguous assignment for the HE and HZ protons bonded to the C-19 carbon. This assignment is especially important since the A ring, and hence the C-19 atom, undergoes a conformational interconversion. The importance of proton nOe difference experiments in determining points of configuration indicate that the assignment of resonances based on allylic coupling constants in a molecule undergoing a conformational equilibrium can be incorrect.