Abstract: Compounds of formula I ##STR1## and pharmaceutically acceptable salts thereof in which one of A or B represents N and the other represents N or C--R.sub.3 ; R.sub.1 represents hydrogen, halo, alkyl, hydroxy, carboxyalkenyl, alkoxycarbonylalkenyl, hydroxyalkyl, carboxyalkyl, alkoxycarbonylalkyl, alkoxy, halogenated alkyl, carboxy, alkoxycarbonyl, alkanoylamino or carbamoylalkenyl; R.sub.2 represents hydrogen, alkyl, halo, alkoxy, hydroxy, alkanoyloxy, or phenoxy; R.sub.3 represents hydrogen or alkyl; R.sub.4 represents hydrogen, halo, alkoxycarbonyl, cyano, benzyloxycarbonyl, alkanoyl, benzoyl, alkyl, carboxy, alkylthio or carbamoyl; R.sub.5 represents hydrogen or alkyl; R.sub.9 represents hydrogen or alkyl; R.sub.10 represents phenyl, pyridyl or pyrimidinyl substituted by OR.sub.6 and optionally further substituted wherein R.sub.6 represents hydrogen, alkyl, alkoxycarbonyl or carbamoyl, alicyclic hydrocarbon, phenyl, cycloalkylalkyl, arylalkyl or pyridyl; or when R.sub.10 represents phenyl, OR.sub.