New furanone derivatives, process for preparation thereof and use thereof

A method comprising administering an effective amount of a compound or its pharmaceutically acceptable salt to a subject in need of treatment of diabetic cataract and/or neuropathy, said compound being of the formula:

• ##STR7## wherein A is a lower alkylene group;
• R.sup.1 is a carboxy, hydroxy, lower alkoxycarbonyl, lower alkoxycarbonylamino, phenyl(lower)alkyloxy, benzoyloxy or lower alkanoyloxy group;
• R.sup.2 is a hydrogen or halogen atom or a halo(lower)alkyl group;
• R.sup.3 is a hydrogen or halogen atom;
• R.sup.4 is hydroxy, lower alkoxy, lower alkanoyloxy or lower alkoxycarbonyloxy group;
• and
• R.sup.5 is a hydrogen or halogen atom;
• Q is the number of double bonds which is equal to 0 or 1;
• n is an integer of 0 or 1, provided that when Q is 0, n is 1 and when Q is 1, n is 0.