Imidazo[1,2-a]quinoxalin-4-amines:: A novel class of nonxanthine A1-adenosine receptor antagonists

The syntheses and A(1) adenosine receptor affinities of a number of imidazo[1,2-alpha]quinoxalin-4-amines are reported. Structure activity relationships within the series and in comparison with other similar tricyclic nonxanthine adenosine antagonists are discussed, leading to a putative common binding mode of these nitrogen-containing heterocycles to A(1) adenosine receptors. Secondary amino compounds displayed the best affinities toward A(1) receptors, while the tertiary amines were almost devoid of activity, thus suggesting a crucial role for the hydrogen bond-forming 4-NH group. Remarkably higher potencies for l-methyl and N-cyclopentyl derivatives were also found. 4-Cyclopentylamino-1-methylimidazo[1,2-alpha]quinoxaline (IRFI 165) is the most potent compound in this series, having K-i(A(1)) = 7.9 nM. It is also provided with a good A(1) selectivity both versus A(2a) and A(3) subtypes and was selected for further pharmacological studies. (C) Elsevier, Paris.