Chemistry and Biological Activity of Vitamin D, its Metabolites and Analogs

Abstract

Publisher Summary This chapter reviews the chemistry and biochemistry of vitamin D and its metabolites and analogs. The new developments in the understanding of the functional metabolism of vitamin D and its regulation have opened a variety of new approaches to the old problems of bone disease on one hand and more theoretical problems of the structure–function relationship with regard to vitamin D on the other. It has been observed that the vitamin has more than one target of action, namely, intestinal calcium absorption, mobilization of calcium from bone, possible calcification of bone, and renal tubular reabsorption of ions. The fact that vitamin D must be metabolized to an active forms before it can function opens new and exciting avenues in the management of a number of metabolic bone diseases. Earlier, Fraser and Kodicek had made the important observation that the tritium deficient metabolite was made solely by the kidney and had demonstrated that this metabolite could be generated in vitro from 25-OH-D 3 with chicken kidney homogenates. The discovery of Steenbock and associates that vitamin D is produced by irradiation of plant and animal sterol fractions led to the synthesis of vitamin D 2 and vitamin D 3 by the irradiation of ergosterol and 7-dehydrocholesterol. Hypoparathyroid patients and patients suffering from vitamin-D-resistant rickets would greatly benefit from administration of 1,25-(OH) 2 D 3 or an analog. The breakthroughs in the understanding of vitamin D metabolism have produced a new profile for the calcium homeostatic mechanisms and the regulation of intestinal calcium absorption.