Compounds of formula (I), wherein R1 is as defined in the claims, exhibit COMT enzyme inhibiting activity and are thus useful as COMT inhibitors. Methods of treatment and pharmaceutical dosage forms are also disclosed.화학식 I의 화합물은 COMT 효소 억제 활성을 나타내고, 따라서 COMT 억제제로서 유용하다.화학식 I상기 화학식 I에서, R1은 특허청구범위에서 정의된 바와 같다.