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 (AR) 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 AR of an AR homodimer. The novel compounds were characterised using radioligand binding assays, including washout assays, and functionally in cAMP assays. The bivalent dicovalent compounds were competitive AR antagonists and showed evidence of covalent binding and simultaneous binding across an AR homodimer. Greater selectivity for AR over the adenosine A 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.