Compounds of general formula (I): ##STR1## in which: R.sub.1, R.sub.2, R.sub.3 and R.sub.4, which may be identical or different, denote a hydrogen atom, a halogen atom or a lower alkyl, lower alkenyl, lower alkyloxy or lower alkenyloxy group, optionally substituted with one or more halogen atoms,R.sub.5 denotes a carboxyl, (lower alkyloxy)carbonyl, (lower alkenyloxy)carbonyl or (lower alkynyloxy)-carbonyl,their isomers, stereoisomers and diastereoisomers, and also their addition salts with a pharmaceutically acceptable base.Medicinal products.