Fluorinated oxysterol analogues: Synthesis, molecular modelling and liver X receptor activity

Abstract

Liver X receptors (LXRs) are nuclear receptors that play central roles in the transcriptional control of lipid metabolism. They also modulate immune and inflammation responses in macrophagues and have multiple roles in cancer biology. The ability of LXRs to integrate metabolic and inflammation signaling makes them particularly attractive targets for intervention in human metabolic diseases. The undesirable effect of LXR agonists on hepatic lipogenesis has prompted the development of LXR antagonists and inverse agonists.2 Several cholestenoic acids are endogenous LXR ligands (e.g. 25R-cholestenoic acid (1)),3 recently we showed that compound 2, a 27-nor analogue of 1, is an inverse agonist and antagonist of LXRs. We have now prepared two fluorinated analogues 3 and 4 from the readily available aldehyde 5. The key step was a Reformatsky reaction with ethyl bromodifluoroacetate under high intensity ultrasound (HIU) irradiation, followed by a BartonMcCombie type deoxygenation to give difluoroester 6 (scheme). LXR activity was evaluated in a luciferase reporter assay in HEK293T cells co-transfected with full length human LXRa and LXRb. At 10 uM the difluoroacid 3 was an inverse agonist and antagonist, similar to its nonfluorinated analog 2, while the difluoroalcohol 4 was an agonist. To investigate the molecular basis of action of ligands 3 and 4, we performed molecular dynamics simulations in our model of LXR.4 The LXR-4 complex maintained a stable agonist conformation similar to that of LXR-GW3965 complex (synthetic agonist) with both fluorine atoms and the 26-hydroxyl alternating in the interaction with His-435. A major change was observed for the LXR-3 complex although different to that observed with inverse agonist 2: Helix-11 is destabilized changing the secondary structure in this region of LXR that carries part of the AF-2 domain (where coactivators and corepressors bind), but without affecting the position of helix-12