Synthesis and pharmacological evaluation of novel 1,3,8- and 1,3,7,8-substituted xanthines as adenosine receptor antagonists.

A number of novel xanthines bearing a variety of substituents at positions 1, 3, 7 and 8 were prepared and evaluated for their binding affinity to the human adenosine receptor A(1), A(2A), A(2B) and A(3) subtypes. Several of the 1,3,8- and 1,3,7,8-substituted xanthines showed moderate-to-high affinity at human A(2B) and A(1) receptors, with the most active compound (14q) having a pK(i) of 7.57 nM for hA(2B) receptors and a selectivity over hA(2A) receptors of 8.1-fold and hA(1) receptors of 3.7-fold.