Abstract: The invention is based on the discovery that compounds of Formula I are unexpectedly highly potent and selective inhibitors of the adenosine A1 receptor. Adenosine A1 antagonists can be useful in the prevention and/or treatment of numerous diseases, including cardiac and circulatory disorders, degenerative disorders of the central nervous system, respiratory disorders, and many diseases for which diuretic treatment is suitable. In one embodiment, the invention features a compound of formula I: R3 is an optionally substituted group selected from: and wherein X1, X2, Z, R1, R2, and R6 are as described in the specification.