Compounds of formula (I) ##STR00001## wherein: X is CH or CH--R.sub.2; R.sub.1 is C.sub.1-C.sub.6 linear or branched alkyl or C.sub.1-C.sub.6 linear or branched alkenyl; R.sub.2 is hydrogen, C.sub.1-C.sub.6 linear or branched alkyl or C.sub.1-C.sub.6 linear or branched alkenyl, C.sub.6-C.sub.14 aryl or C.sub.6-C.sub.14 aryl(C.sub.1-C.sub.6) linear or branched alkyl or C.sub.6-C.sub.14 aryl(C.sub.1-C.sub.6) linear or branched alkenyl, with the aryl group optionally substituted by one or more substituents, either the same or different, selected from the group consisting of halogen, hydroxy, C.sub.1-C.sub.6 alkoxy linear or branched or C.sub.1-C.sub.6 alkenyloxy linear or branched, amino, optionally mono- or disubstituted with C.sub.1-C.sub.6 linear or branched alkyl; R.sub.3 is NH.sub.2, or NHR.sub.4; R.sub.4 is C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 hydroxyalkyl, C.sub.1-C.sub.3 alkoxyalkyl, amino(C.sub.1-C.sub.6)alkyl, where the amino group is optionally substituted with one or two C.sub.1-C.sub.3 linear or branched alkyl groups, or with one or two C.sub.2-C.sub.3 alkenyl groups C.sub.6-C.sub.14 aryl or C.sub.6-C.sub.14 aryl(C.sub.1-C.sub.6)alkyl, with the aryl group optionally substituted by one or more substituents, either the same or different, selected from the group consisting by halogen, hydroxy, C.sub.1-C.sub.6 alkoxy linear or branched or C.sub.1-C.sub.6 alkenyloxy linear or branched, amino, mono- or di-substituted with C.sub.1-C.sub.6 alkyl linear or branched or C.sub.1-C.sub.6 alkenyl linear or branched; and their pharmaceutically acceptable salts. These compounds are antagonists of the adenosine A.sub.2a receptor and useful as medicaments, in particular for the treatment of Parkinson's disease.