Method for stabilizing arylcarboxylic acid, stabilizer thereof and aqueous solution containing stabilized arylcarboxylic acid

A method for stabilizing an carboxylic acid or a pharmacologically acceptable salt thereof, which comprises adding a heterocyclic base of the formula (II):

• wherein
• A and A′ are each a carbon atom or a nitrogen atom;
• X is a carbon atom or a nitrogen atom;
• Y and Z are each a carbon atom or Y and Z taken together optionally form CH;
• R2, R3, R4, R5, R6, R7 and R8 are the same or different and each is a hydrogen atom, a halogen, a carboxyl group, an optionally substituted lower alkyl group, an optionally substituted cycloalkyl group, an optionally substituted acyl group, an optionally substituted aryl group or an optionally substituted heterocyclic group,
• wherein R4 and R5 optionally form a 4- to 6-membered heterocyclic group with the adjacent nitrogen atom and X, and R6 and R7 optionally form a 4- to 6-membered heterocyclic group with the adjacent Y and Z, provided that when X is a nitrogen atom, R5 is void;
• and
• is a single bond or a double bond, provided that when A is a carbon atom, Y and Z are each CH and is a double bond, and when A is a nitrogen atom, Y and Z combinedly form CH and is a single bond,
• to an carboxylic acid of the formula (I):
• L1—R1COOH (I)
• wherein
• L1 is an optionally substituted heterocyclic group having not more than 14 carbon atoms;
• and
• R1 is an optionally substituted alkyl group having not more than 4 carbon atoms or a single bond,
• or a pharmacologically acceptable salt thereof.