Investigation of the thermal isomerization of 1α,25‐dihydroxycholecalciferol by nuclear magnetic resonance spectroscopy

Abstract

This investigation of the kinetics and thermodynamics of the thermal isomerization reaction of la,25-dihydroxycholecalciferol, the physiologically active metabolite of vitamin D3, is based on the simultaneous determinations of la,25-(OH)2D~ and its previtamin analog by nuclear magnetic resonance spectroscopy which distinguishes these compounds from possible impurities. The kinetics at different temperatures are used to obtain the activation parameters for the sigmatropic [ 1,7] thermal interconversion process which is shown to be compatible with a reaction that is unimolecular and concerted. The nature of the transition state of the activated complex, the reaction energetics, and the relative stabilities of la,25-(OH)zD3 and vitamin D3 are discussed.