Synthesis of novel bivalent and multivalent ligands targeting the β₂ adrenergic and A₁ adenosine receptor and the synthesis of functionalised poly-l-lysine dendrimers

Research in the area of simultaneously targeting more than one G protein-coupled receptor (GPCR) with bivalent ligands has increased in recent times. Numerous bivalent ligands have been reported and their functional properties determined. The bivalent ligands may be classed into two groups; (A) ligands binding to GPCR homodimers or (B) ligands binding to GPCR heterodimers. Heterobivalent ligands consist of two different monomeric ligands which bind to their respective receptor ligand and usually separated by a spacer of some sort. These bivalent ligands contain two potential pharmacophores that elicit individual physiological responses. By exploiting the cross talk between the p2-adrenergic (P2AR) and adenosine A, receptors (AiAR) on adenylate cyclase activity, we synthesized a series of bivalent agonists for both GPCRs to generate responses from more than one receptor. We have demonstrated a relationship between the various p2-adrenergic and A, adenosine bivalent parameters of linker and bifunctionality by using data that are drawn from in vitro assays. The bivalent compounds A-(2-hydroxy-5-(l-hydroxy-2-(6-(A'6- adenosinyl) hexylamino)-ethyl) phenyl) formamide (12e) (K„ 311 nM) and N-(2-hydroxy5-(l-hydroxy-2-(4-(A6-adenosinyl) butylamino)-ethyl)phenyl)formamide (12c) (Kj, 863 nM) displayed reasonable binding affinities for the PAR when compared with the control (-)isoproterenol (K;, 136 nM), and both compounds also exhibited a persuasive bifunctional trend for both receptors at various drug concentrations. The bivalent compound 12e was also found to have significant EC50 potency (6 nM) at the p2AR in DDT cells. Compounds 12c and 12e produced potent PAR-mediated stimulation of cAMP with the same maximum response as the full agonist (-) isoproterenol, whereas compounds, A-(5-(2-((2-(2-(jV6-adenosinylethoxy) ethoxy) ethyl) amino)-1 -hydroxyethyl)-2- -IV- hydroxyphenyl)formamide (18) and A-(5-(2-((2-(2-(A6-adenosinyl ethoxy)ethoxy)ethyl) amino)-l-hydroxyethyl)-2-hydroxyphenyl) desformamide (12d) had an AiAR-mediated suppression of the maximal stimulatory response such that they appeared as partial 13- agonists.