Synthesis of a series of 8-(substituted-phenyl)xanthines and a study on the effects of substitution pattern of phenyl substituents on affinity for adenosine A(1) and A(2A) receptors.

A new series of 8-(substituted-phenyl)xanthines have been synthesized and compounds were evaluated for their affinity for A(1) and A(2) adenosine receptors (AR) using radioligand binding assays. The effects of varying the positions of 8-phenyl substituents on affinity and selectivity at A(1) and A(2A) adenosine receptors have been studied. Isovanilloid 1,3-dimethyl-8-[4-methoxy-3-(2-morpholin-4-ylethoxy)phenylxanthine (9d) displayed the highest affinity and selectivity towards A(2A) AR subtypes with K(i)=100nM over A(1) receptors (Ki>100mM). It has been observed that substitution pattern on 8-phenyl group greatly affects the affinity and selectivity at adenosine receptors, with A(2A) tolerating bulkier substituents than did A(1) receptors.