Synthesis and biological activity of 1 alpha,23,25,26-tetrahydroxyvitamin D3

Concise synthesis of 23-hydroxylated vitamin D3 metabolites

Three 23-hydroxylated vitamin D₃ derivatives, which are metabolites of 25-hydroxyvitamin D₃ produced by CYP24A1 and a related diastereomer, were efficiently synthesized. Each C23 hydroxy unit was constructed by the Claisen condensation reaction with ethyl acetate or the Grignard reaction with 2-methylallymagnesium chloride. Stereochemistry at the C23 position was determined by a modified Mosher's method. The triene structures were constructed by the Wittig-Horner reaction utilizing the A-ring phosphine oxide moiety.

The avian as an animal model for the study of the vitamin D endocrine system

This paper presents a summary of experimental studies which utilized the White Leghorn cockerel, Gallus domesticus, as a suitable avian model for a detailed analysis of the mode of action of the seco-steroid vitamin D. It is now apparent that there exists a complex endocrine system which coordinates the metabolism of the parent vitamin D into a family of over 30 metabolites; the principal metabolites are 1,25(OH)2D3 and 24R,25(OH)2D3, which together orchestrate the spectrum of biological responses attributable to vitamin D. Key advances in elucidation of the scope of vitamin D endocrine system include the tissue distribution of both its steroid receptor and its gene-induced product, a 28,000 dalton calcium binding protein, termed calbindin-D28k. To date no less than 23 tissues have been found to have specific 1,25(OH)2D3 receptors; of these at least 10 were identified in avian studies. Similarly, nine avian tissues have been found to express the vitamin D-induced calcium binding protein, calbindin-D28k. These observations collectively demonstrate both the broad scope of the vitamin D endocrine system and the appropriateness of using avians as valid models for vitamin D endocrine research which has applicability and validity for mammals, including man.