Substituted 1,3-dipropylxanthines as irreversible antagonists of A1 adenosine receptors

This report describes the synthesis of 29 xanthines containing a chemoreactive chloroaryl, beta-chloroethylamino, alpha,beta-unsaturated carbonyl, bromoacetyl, 3-(fluorosulfonyl)benzoyl, or 4-(fluorosulfonyl)benzoyl group as part of an exocyclic 1-, 3-, or 8-substituent. The xanthines inhibited the binding of [3H]-8-cyclopentyl-1,3-dipropylxanthine ([3H]CPX) to the A1 adenosine receptor (A1AR) of DDT1 MF2 cells at IC50s in the low-nanomolar to low-micromolar range. Seven of the 29 analogues irreversibly inhibited the binding of [3H]CPX without changing the KD of that ligand; five were 1,3-dipropylxanthines having the following reactive groups as 8-substituents: (bromoacetamido)methyl (24), (bromoacetamido)ethyl (25), (bromoacetamido)propyl (26), [4-(fluorosulfonyl)benzamido]methyl (33) or 3-[[4-(fluorosulfonyl)benzoyl]oxy]cyclopentyl (42). Both 8-cyclopentyl-3-[3-[[4- (fluorosulfonyl)benzoyl]oxy]propyl]-1-propylxanthine (53) and 8-cyclopentyl-1,3-bis[3-[[4- (fluorosulfonyl)benzoyl]oxy]propyl]xanthine (55) inhibited [3H]CPX binding irreversibly. Five of the ligands, including 26, 33 (IC50 = 49 microM), and 53 (IC50 = 9 microM), antagonized the binding of [3H]NECA to the A2aAR of PC12 cells, but unlike binding to the A1AR, binding to the A2aAR was completely reversible. The potency of 33 (IC50 = 2 microM, 72% loss of CPX binding at 1 microM) and 53 (IC50 = 0.01 microM, 74% loss of CPX binding at 0.05 microM) and their selectivity for the A1AR suggest that those two ligands may be useful in studies of the structure and function of that receptor.