Disclosed is a novel compound having P2X3 or P2X2/3 receptor antagonisticeffect. Specifically disclosed is a compound represented by formula (I). (Intheformula, (a) R a and R b combine together to form =Z, and R c is a grouprepresentedby R1c, or alternatively (b) R b and R c combine together to form a bond, andR a is a group represented by -Y-R1a； R1a and R1c each independentlyrepresents ahydrogen atom, a substituted or unsubstituted alkyl group or the like； R2 andR3 each independently represents a substituted or unsubstituted aryl group orthelike； R4a and R4b each independently represents a hydrogen atom, a substitutedor unsubstituted alkyl group or the like； X represents -N(R5)- or the like； R5represents a hydrogen atom, a substituted or unsubstituted lower alkyl grouporthe like； Y represents -O- or the like； Z represents =O or the like； and nrepresentsan integer of 0-4.)
