The invention relates to a compound, and pharmaceutically acceptable salts, having the formula I: ##STR00001## wherein: R represents an alkyl or alkynyl group having 1-4 carbon atoms, or a phenyl group optionally substituted by C.sub.1-4 alkyl, alkylthio, alkoxy, halogen, nitro, acylamino, methylsulfonyl or methylenedioxy, or represents tetrahydronaphthyl, R.sup.1 represents hydrogen, trifluoro (C.sub.1-4) alkyl, alkyl or alkynyl, X represents hydrogen, alkyl having 1-4 carbon atoms, alkoxy, trifluoroalkyl, hydroxy, halogen, methylthio or aralkoxy, R.sup.2 represents: a C1-C10 alkyl group, a phenyl group optionally substituted by one or more of the following groups: a C1-C10 alkyl group, a halogen group, a nitro group, hydroxy group, and/or an alkoxy group.