Ring-A-seco analogs of 1α,25-dihydroxy-19-norvitamin D3.

The steroid hormone 1α,25-dihydroxyvitamin D3 [1α,25-(OH)2D3] is the most active metabolite of vitamin D3 which exerts its control over a multitude of biological processes related to calcium and phosphorus homeostasis, cell proliferation and differentiation, and immune regulation. Unfortunately, the therapeutic application of 1α,25-(OH)2D3 is limited by induction of hypercalcemia. The need for vitamin D compounds with selective biological profiles has stimulated the synthesis of more than three thousand analogs of 1α,25-(OH)2D3. Most of these compounds have structural modifications in the side chain and A-ring; there is also an increasing number of modifications in the CD-rings and limited number in the triene system (seco-B ring). Herein, we report the synthesis and biological evaluation of seco-A-19-nor analogs of 1α,25-dihydroxyvitamin D3, developed to study the role of ring A in the biological activity of 1α,25-(OH)2D3. Interestingly, compounds 2 and 4 show substantial ability to bind the vitamin D receptor and the former is also characterized by selective intestinal calcium transport activity. This article is part of a Special Issue entitled 'Vitamin D Workshop'.