The present invention provides compounds represented by general formula (I):or pharmaceutical acceptable salts thereof, wherein R1 and R2 are each hydrogen, lower acyl, lower alkoxycarbonyl or the like R3 is lower alkyl, halo-lower alkyl, cycloalkyl, heterocycloalkyl, optionally substituted aryl, optionally substituted heteroaryl or the like R4 is cyano, lower alkoxycarbonyl, carboxy or the like, which exhibit potent COMT inhibitory activities. The present invention also provides pharmaceutical compositions containing said compound, and uses thereof.
