chain of an amino acid having at least one free carboxylic acid group, R1 is a hydrogen atom or a pharmaceutically acceptable metal salt, R2 is a single amino acid connected to the --SO2 bridge through its amine function, R3 is --CH2 --CO--NH--R4, R4 is alkyl, phenyl or benzyl, and further when X is --SO3 R1, then at least one of Y or V is other than H and where V is --CH2 --CO--NH--CHR--COOH, at