Abstract: Compounds of general formula (I): ##STR1## in which: R.sub.1 represents a hydrogen atom or a lower alkyl group,A represents a hydrogen atom, and in this case B represents a group CO-G, G being:either a heteroaryl group selected from furan, indole, pyrrole, pyridine, quinoline, isoquinoline and benzofuran, optionally substituted with one or more lower alkyl or lower alkoxy groups or a halogen atoms,or a linear or branched lower alkyl group substituted with a carboxyl group,or a linear or branched lower alkenyl group substituted with a carboxyl group,or a phenyl or naphthyl group substituted with a carboxyl group,or alternatively A forms with B a group CO(CH.sub.2).sub.n CH(CH.sub.