Bicyclic compounds

A compound of the formula [I] and pharmaceutically acceptable salts thereof, ##STR9## wherein R.sup.1 and R.sup.2 are the same or different and each is hydrogen or a straight or branched chain alkyl having 1 to 6 carbon atoms;

• R.sup.3 and R.sup.4 are the same or different and each is hydrogen, a straight or branched chain alkyl having 1 to 6 carbon atoms, carboxy or lower alkoxycarbonyl;
• R.sup.5 is hydrogen or straight or branched chain alkyl having 1 to 6 carbon atoms;
• X is oxygen or NR.sup.6 ;
• R.sup.6 is hydrogen, lower alkyl, lower alkoxy, phenyl lower alkyl or phenyl lower alkoxy, and the said lower alkyl can be substituted by carboxy, lower alkoxycarbonyl, amino, lower alkylamino, lower alkoxycarbonylamino or phenyl lower alkylamino, and the phenyl ring of the said phenyl lower alkyl, phenyl lower alkoxy or phenyl lower alkylamino can be substituted by lower alkyl, lower alkoxy, fluorine, chlorine, bromine, iodine, carboxy or lower alkoxycarbonyl wherein each lower alkyl is a straight or branched alkyl having 1 to 6 carbon atoms, and each lower alkoxy is a straight or branched alkoxy having 1 to 6 carbon atoms;
• A is straight or branched alkylene having 1 to 6 carbon atoms,
• n is 0 to 1.