Abstract: The compound of the formula: ##STR1## wherein: R.sub.1 and R.sub.2 are, independent from each other, hydrogen, C.sub.1-10 straight chain alkyl, C.sub.1-10 branched alkyl, or C.sub.3-10 cyclic or bicyclic alkyl;R.sub.3 is an acyl substituent selected from the group consisting of formyl, alkanoyl of 2 to 7 carbon atoms, alkenoyl of 3 to 7 carbon atoms, alkylsulfonyl of 1 to 7 carbon atoms, aroyl of 7 to 12 carbon atoms, arylalkenoyl of 9 to 20 carbon atoms, arylsulfonyl of 6 to 12 carbon atoms, arylalkanoyl of 8 to 12 carbon atoms or arylalkylsulfonyl of 7 to 12 carbon atoms;A is selected from the group consisting of: ##STR2## wherein: R.sub.4 is hydrogen, C.sub.1-6 alkyl, C.sub.1-6 perfluoroalkyl, C.sub.1-6 alkoxy, C.sub.1-6 perfluoroalkoxy, amino, C.sub.1-6 alkylamino, C.sub.2-12 dialkylamino, C.sub.1-6 alkylsulfonamido, alkylcarboxamido containing 2 to 7 carbon atoms, nitro, cyano or carboxyl;or a pharmaceutically acceptable salt thereof, are smooth muscle relaxants.