Compounds of formula (I) are A2B receptor antagonists: Wherein R1 is optionally substituted aryl or an optionally substituted 5- or 6-membered heteroaryl ring; R2 and R3 are independently selected from hydrogen, C1-C6 alkyl, C3-C8 cycloalkyl, C3-C8 cycloalkyl-(C1-C6)-alkyl, aryl-(C1-C6)-alkyl optionally substituted in the ring part thereof, a 5- or 6-membered monocyclic heterocyclic group optionally linked via a C1-C6 alkylene chain and optionally substituted in the ring part thereof, benzimidazol-2-yl-methyl, pyrid-3-yl-carbonyl, or (1-methyl-piperidin-4-yl)-carbonyl-methyl; or R2 and R3 taken together with the nitrogen atom to which they are attached form an optionally substituted 5- or 6-membered ring; R4 is C1-C3 alkyl, C2-C3 alkenyl, —N(—R5)—R6, or optionally substituted heteroarylmethylamino; and R5 and R6 are independently selected from hydrogen or C1-C3 alkyl; or R5 and R6 taken together with the nitrogen atom to which they are attached form an optionally substituted 4- to 6-membered saturated ring.