A series of 8-phenylxanthine derivatives has been synthesized with oxyacetic acid on the para phenyl position to increase aqueous solubility and minimize nonspecific binding and iodinatable groups on the 1-or 3-position of the xanthine ring. The structure-activity relationship for binding of these compounds to A, adenosine receptors of bovine and rat brain and A, receptors of human platelets was examined. The addition of arylamine or ...