Development of Putative Bivalent Dicovalent Ligands for the Adenosine A1 Receptor

Accumulating evidence suggests that G protein-coupled receptors (GPCRs) can exist and function in homodimer and heterodimer forms. The adenosine A1 receptor (A₁R) has been shown to form both homodimers and heterodimers, but there is a lack of chemical tools to study these dimeric receptor populations. This work describes the synthesis and pharmacological evaluation of a novel class of bivalent GPCR chemical tools, where each ligand moiety of the bivalent compound contains a sulfonyl fluoride covalent warhead designed to be capable of simultaneously reacting with each A₁R of an A₁R homodimer. The novel compounds were characterised using radioligand binding assays, including washout assays, and functionally in cAMP assays. The bivalent dicovalent compounds were competitive A₁R antagonists and showed evidence of covalent binding and simultaneous binding across an A₁R homodimer. Greater selectivity for A₁R over the adenosine A₃ receptor was observed for bivalent dicovalent over the equivalent monovalent compounds, indicating subtype selectivity can be achieved with dual occupation by a bivalent dicovalent ligand.