CONICET | Buscador de Institutos y Recursos Humanos

The nematode worm Caenorhabditis elegans (ce) is an important model organism for biomedical research.1 The study of the nuclear receptor ceDAF-12, has acquired special attention because it is involved in multiple physiological functions, such as developmental timing, metabolism, fertility and longevity.2 Its ligands named dafachronic acids, are C-27 cholesterol metabolites, compounds 1 and 3 being the most active and abundant in the animal. The configuration of the C-25 methyl group is an important determinant on the activity of the ligand-receptor complex; transactivation assays and in vivo experiments have shown that the 25S dafachronic acids (1, 3) are more active than the 25R diastereoisomers (2, 4). Recently, we developed a model for the ligand binding domain (LBD) of the ceDAF-12 receptor, that allowed us to simulate its complexes with ligands 3 and 4 using molecular dynamics and explain their relative activities at the molecular level.3 The model showed that removal of the C-25 methyl would not impede the strong interaction of the carboxylate with the NR, predicting that the 27-nor-dafachronic acids are putative ceDAF-12 ligands. Based on these findings, we report the molecular dynamics study for the binding of the 27-nor-dafachronic acid 5, its synthesis and biological activity in vitro. Compound 5 was prepared by two sequential 2-carbon homologations of aldehyde 6 (Scheme). The key steps for this transformation were two Wittig reactions each followed by regioselective reduction of the side chain double bond. Compound 5 induced DAF-12 activity in transient transfections of GAL4-DAF12 and GAL4-LUC reporter in HEK-293T cell cultures. Molecular dynamics simulation of the ceDAF-12-LBD/5 complex showed that the side-chain of 5 adopts mostly a torsioned conformation and the carboxylate binds strongly to the 3 arginines in the LBD.

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