Compounds having effects to dilate coronary artery and peripheral blood vessels and to depress the blood pressure, and useful as drugs for cardiovascular disease are represented by the following general formula:
wherein R, represents a hydrogen atom, an alkyl group having 1-5 carbon atoms, an alkenyl group having 2-5 carbon atoms, an aralkyl group having 7-13 carbon atoms or an acyl group having 1-7 carbon atoms, R. and R 3 are the same or different groups and each represents a substituted or unsubstituted alkyl group having 1-5 carbon atoms, an alkenyl group having 2-5 carbon atoms, a disubstituted aminoalkyl group having 1-5 carbon atoms or a substituted or unsubstituted heterocyclic group, R 4 and R 5 are the same or different groups and each represents a hydrogen atom, a halogen atom or a nitro group, and R 6 and R 7 are the same or different groups and each represents an alkyl group having 1-5 carbon atoms; the pharmaceutically acceptable acid addition salt thereof are also effective therapeutic compounds.