A compound of formula I wherein M is one of the groups M A, M B and M C represented below and either R 1 represents H and, when M is M A, R 2 represents SO 3 H, phosphonooxymethyl or the group L 2A represented below wherein R 2A represents (C 1 -C 4)alkylamino(C 1 -C 4)alkyl, [di(C 2 -C 4)alkylamino]methyl, {(methyl)[(C 2 -C 4)alkyl]amino}methyl, [di(C 1 -C 4)alkylamino](C 2 -C 4)alkyl, morpholin-4-yl-(C 1 -C 4)alkyl, phosphonooxy(C 1 -C 4)alkyl, 2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4)alkyl or [2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl]-(C 1 -C 4)alkyl, or, when M is M B or M C, R 2 represents PO 3 H 2, SO 3 H, phosphonooxymethyl or the group L 2BC represented below wherein R 2BC represents (C 1 -C 4)alkylamino(C 1 -C 4)alkyl, [di(C 1 -C 4)alkylamino](C 1 -C 4)alkyl, morpholin-4-yl-(C 1 -C 4)alkyl, phosphonooxy(C 1 -C 4)alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4)alkyl or [2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl]-(C 1 -C 4)alkyl, or R 2 represents H and R 1 represents PO 3 H 2, SO 3 H, phosphonooxymethyl or the group L 1 represented below wherein R 1A represents (C 1 -C 4)alkylamino(C 1 -C 4)alkyl, [di(C 1 -C 4)alkylamino](C 1 -C 4)alkyl, morpholin-4-yl-(C 1 -C 4)alkyl, phosphonooxy(C 1 -C 4)alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4)alkyl or [2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl]-(C 1 -C 4)alkyl; it being understood that the molecule is always such that its R 2 group is attached to the oxygen atom of its M A, M B and M C group; or a salt of this compound. M is one of the groups M A, M B and M C represented below and either R 1 represents H and, when M is M A, R 2 represents SO 3 H, phosphonooxymethyl or the group L 2A represented below wherein R 2A represents (C 1 -C 4)alkylamino(C 1 -C 4)alkyl, [di(C 2 -C 4)alkylamino]methyl, {(methyl)[(C 2 -C 4)alkyl]amino}methyl, [di(C 1 -C 4)alkylamino](C 2 -C 4)alkyl, morpholin-4-yl-(C 1 -C 4)alkyl, phosphonooxy(C 1 -C 4)alkyl, 2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4)alkyl or [2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl]-(C 1 -C 4)alkyl, or, when M is M B or M C, R 2 represents PO 3 H 2, SO 3 H, phosphonooxymethyl or the group L 2BC represented below wherein R 2BC represents (C 1 -C 4)alkylamino(C 1 -C 4)alkyl, [di(C 1 -C 4)alkylamino](C 1 -C 4)alkyl, morpholin-4-yl-(C 1 -C 4)alkyl, phosphonooxy(C 1 -C 4)alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4)alkyl or [2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl]-(C 1 -C 4)alkyl, or R 2 represents H and R 1 represents PO 3 H 2, SO 3 H, phosphonooxymethyl or the group L 1 represented below wherein R 1A represents (C 1 -C 4)alkylamino(C 1 -C 4)alkyl, [di(C 1 -C 4)alkylamino](C 1 -C 4)alkyl, morpholin-4-yl-(C 1 -C 4)alkyl, phosphonooxy(C 1 -C 4)alkyl, phosphonooxymethoxy, 2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl, (2-(phosphonooxy)-phenyl)-(C 1 -C 4)alkyl or [2-(phosphonooxy-(C 1 -C 4)alkyl)-phenyl]-(C 1 -C 4)alkyl; it being understood that the molecule is always such that its R 2 group is attached to the oxygen atom of its M A, M B and M C group; or a salt of this compound.