In the present invention, a novel 2-alkynyl-N9-propargyladenine represented by formula (I)wherein R1 represents a halogen atom, a furyl group, or a triazolyl group R2 and R3 each represents a hydrogen atom or a C1-8 alkyl group, or form a cycloalkyl group by bonding to each other and X represents a hydrogen atom or a hydroxyl group, or a pharmaceutically acceptable salt thereof, has a stronger and longer-lasting effect as a therapeutic agent for Parkinsonian syndromes.
