Vitamin D Analogues via Dynamic Combinatorial Chemistry

Calcitriol (1alpha,25-(OH)2D3, 1,25D) is known for its calcium regulatory function, but also for being a powerful inhibitor of cell growth in a variety of normal and neoplastic cells. As such, it is a lead structure in the development of new cancer drugs. The goal of our project is to identify analogues of calcitriol which bind tightly to the vitamin D receptor (VDR) yet do not exhibit unwanted hypercalcemic effects. The development of novel analogues using conventional chemistry and dynamic chemistry was investigated. First, the numerous building blocks required for the exploration of the different libraries were created through the use of conventional techniques. We then developed different synthetic schemes based primarily on thiol alkylation and amide couplings, enabling rapid parallel synthesis of potential 1,25D analogues. Preliminary investigations allowed us to implement with our collaborators a set of biological assays to evaluate our compounds. Although some analogues appeared to bind to the VDR, it was found that none of the 8 analogues tested in the preliminary studies seemed to be vitamin D receptor (VDR) agonists.;Finally, we created dithiol building blocks, amenable to disulfide exchange in dynamic libraries. Chemically stable, these disulfide entities easily generated libraries of at least 30 members from as few as 7 building blocks. Our preliminary disulfide libraries seemed uninfluenced by VDR's presence. These results still allowed us to understand better the characteristics and limitations of dynamic systems applied to the development of novel vitamin D analogues.;In a second part, our research focused on the study of dynamic combinatorial chemistry as a tool for the synthesis of 1,25D analogues. Our first dynamically-generated libraries were created via thioester exchange. It was found that the rate of thioester exchange was dependent on the nature of the thiols involved and the acyl portion of the thioesters. Aliphatic acid thioesters exchanged more slowly than aromatic acid thioesters. The use of branched (alpha-substituted) thiols also slowed the rate compared to primary ones. However, the use of large concentration of aliphatic or aromatic thiols could accelerate the thioester exchange. When thioesters were placed in presence of protein targets in a dynamic system, their inherent electrophilic nature rendered them prone to chemical decomposition (hydrolysis and acylation of protein nucleophilic residues) at basic pHs. Nonetheless, we created thioester libraries of up to 40 members from as few as 7 building blocks under near neutral conditions. We showed that these dynamic libraries ere influenced by the presence of proteins. We have not been able to confirm if thioester libraries were influenced exclusively by the VDR via its binding site. Some of our observations challenged the viability of the thioester exchange as a reversible process in the context of VD 3 analogue synthesis.