An N-containing heterocyclic compound of the formula: ##STR1## wherein R.sup.1 is lower alkyl optionally substituted with hydroxy, halogen or a heterocyclic group, carboxy, esterified carboxy, carbamoyl optionally substituted with heterocyclic(lower)alkyl or lower alkylamino(lower)alkyl, N-containing heterocycliccarbonyl optionally substituted with lower alkyl, or ureido optionally substituted with lower alkylamino(lower)alkyl, andR.sup.3 is hydrogen or halogen;R.sup.2 is phenyl substituted with nitro, andX is .dbd.N--or ##STR2## in which R.sup.4 is lower alkyl or halo(lower)alkyl, or is taken together with R.sup.1 to form an N-containing heterocyclic group optionally substituted with oxo and lower alkylamino(lower)alkyl; orR.sup.2 is lower alkyl, andX is ##STR3## in which R.sup.4 is phenyl substituted with nitro; and a pharmaceutically acceptable salt thereof, processes for the preparation thereof and pharmaceutical (e.g. antihypertension) compositions comprising the same.