Abstract: Compounds of the formula: ##STR1## or tautomeric forms and a pharmaceutically acceptable salt, and pharmaceutically acceptable solvates thereof, wherein:A.sup.1 is a substituted or unsubstituted oxazole substituted by up to 4 substituents selected from the group consisting of C.sub.1-6 -alkyl, C.sub.1-6 -alkoxy, phenyl, and halogen or any two substituents on adjacent carbon atoms, together with the carbon atoms to which they are attached, form a benzene ring, and wherein the carbon atoms of the benzene ring represented by the said two substituents are unsubstituted or substituted with up to three groups selected from halogen, C.sub.1-6 -alkyl, phenyl, C.sub.1-6 -alkoxy, halo-C.sub.1-6 -alkyl, hydroxy, amino, nitro, carboxy, C.sub.1-6 -alkoxycarbonyl, C.sub.1-6 -alkoxycarbonyl-C.sub.1-6 -alkyl, C.sub.1-6 -alkylcarbonyloxy, and C.sub.1-5 -alkylcarbonyl;R.sup.l is a hydrogen atom, a C.sub.1-6 -alkyl group, a C.sub.1-6 -alkylcarbonyloxy group, a phenyl-C.sub.