Adenosine receptor antagonist 5 (Compound 39) is a selective antagonist for human adenosine A3 receptor (hA3R) with K i of 12 nM. Adenosine receptor antagonist 5 inhibits IB-MECA -induced cAMP accumulation in NCI-H1792 cell, inhibits the proliferation of cancer cell LK-2 and NCI-H1792. Adenosine receptor antagonist 5 exhibits a fast metabolic rate in human liver microsomes.