Novel A-ring homodimeric C-3-carbamate analogues of 1a,25-dihydroxyvitamin D 3 : Synthesis and preliminary biological evaluation Daniel Oves, a Susana Ferna ´ndez, a Lieve Verlinden, b Roger Bouillon, b Annemieke Verstuyf, b Miguel Ferrero a and Vicente Gotor a, * a Departamento de Quı ´mica Orga ´ nica e Inorga ´ nica and Instituto Universitario de Biotecnologı ´a de Asturias, Universidad de Oviedo, 33006-Oviedo (Asturias), Spain b Laboratorium voor Experimentele Geneeskunde en Endocrinologie, Katholieke Universiteit Leuven, Gasthuisberg, B-3000 Leuven, Belgium Received 24 May 2006; revised 30 June 2006; accepted 6 July 2006 Available online 1 August 2006 Abstract—The synthesis of a new class of vitamin D 3 analogues in which two units of 1a,25-dihydroxyvitamin D 3 are linked at the C-3 position by a dicarbamate functionality of variable length is described. The analogues demonstrated no affinity for the vitamin D receptor and possessed no antiproliferative or transactivating properties. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction 1a,25-Dihydroxyvitamin D 3 [1a,25-(OH) 2 -D 3 , 1, Figure 1], the most active metabolite of vitamin D 3 (2), plays a major role in many biological processes including calcium–phosphorus homeostasis, cell differentiation and proliferation, and immune reactions. 1 However, the mechanisms for these differential actions have not been clearly defined. In the last two decades, various analogues 2 of 1a,25-(OH) 2 -D 3 have been developed to improve the biological profile of the natural hormone for a potential therapeutic application. 3 Some of these derivatives have similar or more potent antiproliferative, yet reduced hypercalcemic actions, than the natural hor- mone. An increasing number of synthetic vitamin D derivatives are currently in use as drugs for treatment of various human diseases and new candidates are in human clinical trials. 2a,4 The genomic actions of 1a,25-(OH) 2 -D 3 are mediated by the vitamin D nuclear receptor (n-VDR), which is a member of the nuclear steroid hormone receptor super- family. 5 Structure-function analysis of the n-VDR protein reveals distinct domains involved in nuclear localization, DNA binding, ligand binding, receptor dimerization, and gene transactivation. 6 It is believed that n-VDR-mediated gene expression is initiated by binding of 1a,25-(OH) 2 -D 3 to the ligand binding domain of n-VDR which is assumed to cause conformational changes in the receptor protein. Thus, a detailed under- standing of the complementarity of the ligand shape with that of the interior surface of the nuclear VDR receptor ligand domain is the key to understand not only the structural basis of receptor action, but also to design new analogues of 1a,25-(OH) 2 -D 3 . The n-VDR is a ligand-dependent transcription factor that regulates target gene expression by interacting with response ele- ments in gene promoters. 0968-0896/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.bmc.2006.07.021 Keywords: Vitamin D 3 analogues; Enzymatic catalysis; Biological evaluation. * Corresponding author. Tel./fax: +34 98 510 3448; e-mail: vgs@fq. uniovi.es R 1 R 2 R 3 H 1 3 25 1, R 1 = R 2 = R 3 = OH, 1α,25-Dihydroxyvitamin D 3 2, R 1 = R 3 = H; R 2 = OH, Vitamin D 3 Figure 1. 1a,25-Dihydroxyvitamin D 3 , the most active metabolite of vitamin D 3 . Bioorganic & Medicinal Chemistry 14 (2006) 7512–7519