KF-26777 is a drug which acts as a potent and selective antagonist for the adenosine A₃

Adenosine A3 receptor

The adenosine A3 receptor, also known as ADORA3, is an adenosine receptor, but also denotes the human gene encoding it.- Function :Adenosine A3 receptors are G protein-coupled receptors that couple to Gi/Gq and are involved in a variety of intracellular signaling pathways and physiological functions...

 receptor

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

, with sub-nanomolar affinity (A₃ Ki=0.2nM) and high selectivity over the other three adenosine receptor

Adenosine receptor

The adenosine receptors are a class of purinergic receptors, G protein-coupled receptors with adenosine as endogenous ligand.-Pharmacology:...

 subtypes. Simple xanthine

Xanthine

Xanthine , is a purine base found in most human body tissues and fluids and in other organisms. A number of stimulants are derived from xanthine, including caffeine and theobromine....

 derivatives such as caffeine

Caffeine

Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...

 and DPCPX have generally low affinity for the A₃ subtype and must be extended by expanding the ring system and adding an aromatic group to give high A₃ affinity and selectivity.