The invention relates to a compound of the formula I in which: R.sub.1 represents, independently of each other, a halogen atom; an aliphatic hydrocarbon-based group optionally substituted and/or optionally interrupted by one or more oxygen or sulfur atoms; a nitro group; a cyano group; an amino group; a mono- or dialkylamino group; an alkylcarbonyl group; a carboxyl group; an alkylcarbonylamino group; an alkylsulfonyl group; R.sub.2 represents, independently of each other, a cyano group; a hydroxyl group, an alkylcarbonyl group; a carboxyl group; an alkoxycarbonyl group; an unsubstituted amide group; or a linear or branched alkyl group substituted by a cyano, hydroxyl, carboxyl, alkoxycarbonyl or unsubstituted amide group; i and j independently being 1 to 5, with the exclusion of the compound for which i and j=1 and R.sub.1=carboxyl and R.sub.2=alkoxycarbonyl or R.sub.1=CF.sub.3 and R.sub.2=carboxyl, and also the pharmaceutically acceptable derivatives, salts, solvates and stereoisomers thereof, including mixtures thereof in all proportions.