The present invention provides compounds represented by general formula (I): or pharmaceutical acceptable salts thereof, wherein R 1 and R 2 are each hydrogen, lower acyl, lower alkoxycarbonyl or the like R 3 is lower alkyl, halo-lower alkyl, cycloalkyl, heterocycloalkyl, optionally substituted aryl, optionally substituted heteroaryl or the like R 4 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.
