Abstract
The active form of vitamin D(3), 1α,25-dihydroxyvitamin D(3) (1,25D(3)), regulates a number of physiological and pathological processes, including cell proliferation and differentiation. Thousands of analogues of 1,25D(3) have been developed with the aim of selective effects for medical use. Here we describe the synthesis of two new unconventional vitamin D analogues bearing A-ring modifications with ortho-carborane (dicarba-o-closo-1,2-dodecaborane) units. The ligands function as agonists for VDR with similar antiproliferative activities as 1,25D(3). Whereas mice treated with the analogues 4 and 5 exhibited similar hypercalcemic activities as 1,25D(3), only compound 4 and 1,25D(3) induced the strong activation of CYP24A1 mRNA expression but not compound 5.