Synthesis of 8-(cyclopentyloxy)phenyl substituted xanthine derivatives as adenosine A2A ligands

The present paper describes the synthesis of a series of 8-(cyclopentyloxy)phenyl-xanthines and their evaluation for affinity for A1 and A2 adenosine receptors using radioligand binding assays. The effects of moving the cyclopentyloxy substituent with or without an ortho methoxy group on the various positions of the 8-phenyl ring have been studied. The vanilloid based xanthines 8-[4-(cyclopentyloxy)-3-methoxyphenyl]-1,3-dimethylxanthine (6a) (K(i)= 100 nM) and 8-[(4-cyclopentyloxy)-3-methoxyphenyl] -3-methyl-1-propylxanthine (12) (K(i) = 150 nM) displayed the highest affinity at A2A receptors as well as over 1000 fold selectivity over the A1 adenosine receptor subtype.