Compounds having the structural formula I or a pharmaceutically acceptable salt thereof, wherein R is R1-isoxazolyl, R1-oxadiazolyl, R1-dihydrofuranyl, R1-pyrazolyl, R1-imidazolyl, R1-pyrazinyl or R1-pyrimidinyl; R1 is 1, 2 or 3 substituents selected from H, alkyl, alkoxy and halo; Z is optionally substituted-aryl, or optionally substituted-heteroaryl; are disclosed, as well as their use in the treatment of central nervous system diseases, in particular Parkinson's disease and Extra Pyramidal Syndrome, pharmaceutical compositions comprising them, and combinations with other agents.