Compounds of the general formula (I): ##STR1## and pharmaceutically acceptable salts thereof, in whichA, B, C and D each represent --CH.dbd. or --N.dbd., with the proviso that at least one of them is --N.dbd.;X represents --NH--, --O-- or --S--;Y represents --(CH.sub.2).sub.p -- wherein p is an integer from 0 to 4, --C(CH.sub.3).sub.2 --, --CH.sub.2 CH.dbd.CH--, --CH.sub.2 CO--, --CF.sub.2 -- or --CH.sub.2 COCH.sub.2 --;R.sup.1 represents a hydrogen atom, a C.sub.1-4 alkyl group, a halogen atom or a C.sub.1-4 alkoxy group;R.sup.2 represnts a hydrogen atom, a hydroxyl group, a saturated or unsaturated C.sub.1-6 alkyl group, a C.sub.1-6 alkoxy group, a carboxyl group, a saturated or unsaturated C.sub.1-12 alkoxycarbonyl group which may be optionally substituted, a cycloalkoxycarbonyl group, a saturated or unsaturated five- or six-memebered heterocyclic group containing at least one nitrogen atom optionally with one or more nitrogen and/or oxygen atoms, which may be optionally condensed and/or substituted, --CONR.sup.3 R.sup.4, --NR.sup.3 R.sup.4, --OCOR.sup.3 or --NHCONHR.sup.3 wherein R.sup.3 and R.sup.4, which may be the same or different, represent a C.sub.1-6 alkyl group which may be optionally substituted or a cycloalkyl group, andm and n each represent an integrer from 0 to 2.The compounds are useful in treating ulcers.