A compound with hypoglycaemic activity having formula (II) or a pharmaceutically acceptable ammonium or acid addition salt thereof:
wherein
R' and R 2 are the same or different and represent hydrogen, Ci-6 alkyl, C 1-6 alkoxy, hydroxy or halogen; R 3 and R' are the same or different and represent hydrogen or C 1-6 alkyl; R' represents hydrogen or C 1-6 alkyl; R 6 represents C 1-6 alkyl, phenyl optionally substituted with up to 3 groups selected from halogen, C 1-6 alkyl, and C 1-6 alkoxy; or benzyl optionally substituted with up to 3 groups selected from halogen, C 1-6 alkyl and C 1-6 alkoxy; or R 5 and R 6 together represent the remaining members of a 5- or 6- membered ring optionally containing an oxygen, sulphur or additional nitrogen atom and being optionally substituted with C 1-6 alkyl, carboxy or C 1-6 alkoxycarbonyl; and R' represents phenyl, optionally substituted with up to 3 groups selected from halogen, C 1-6 alkyl and C 1-6 alkoxy, C 1-6 alkoxy carbonyl, C 1-6 alkanoyl, C 1-6 alkyanoyloxy, nitro, hydro, amino, substituted amino, and carboxy.