Synthesis, Identification, and Chemoenzymatic Functionalisation of Inhibitors of Sterol Transport Proteins

Sterol transport proteins (STPs) mediate intracellular sterol transport, organelle contact sites, and lipid metabolism. Their mis-regulation has been associated with lipid storage disorders, atherosclerosis, and a wide range of cancers. Despite their importance, the similarities in their sterol-binding domains have made the identification of selective modulators difficult. Crucially, very few STP inhibitors have been reported, often with little or no selectivity annotations, and the majority of these target a small fraction of STPs, highlighting a significant gap in the field. Therefore, the development of potent and selective small molecule STP inhibitors is of great significance for both basic and translational lipid biology.
To address this problem, a novel cholic-acid inspired compound collection of consisting of 69 molecules was synthesised through the combination of different compound library synthesis strategies for the identification of potent and selective modulators of STPs. The fusion of the cisdecalin AB-ring system as found in cholic acid as a primary sterol scaffold with a range of different fragments found in natural products followed by various ring distortions enabled the synthesis of diverse sterol-inspired compounds. Through the screening of the analogues by fluorescence polarisation, differential scanning fluorimetry, and cholesterol transport assays, the complex and three-dimensional spirooxepinoindole was identified as a privileged scaffold for STPs. With careful optimisation of the scaffold the selectivity could be directed towards a single transporter, as showcased by the development of (−)-Asteroxin-1 as a potent and selective Aster-A inhibitor (Figure 1).
In the effort to further improve potency and selectivity of the lead compound, late-stage chemoenzymatic functionalisation of (–)-Asteroxin-1 and its late intermediates was performed (Figure 1) achieving both enzyme- and substrate-dependent selectivity and oxidation sites not easily accessible by classical chemical means.