A compound of the formula (I): wherein A is an aromatic or heteroaromatic ring system or partially or fully reduced derivatives thereof； Q is hydrogen, C 1 -C 12 straight chain, branched or cyclic alkyl substituted with one or more hydroxy groups, or a mono- or di-saccharide moiety； Z is -CR 10 R 11 -, -NR 12 -, -C(O)O-, -C(O)NR 12 - or -O-, where R 10 and R 11 are independently selected from hydrogen, hydroxy, C 1 -C 6 alkyl, C 6 -C 10 aryl, C 1 -C 6 alkoxy and -N(R 13 ) 2 and where each R 13 is independently selected from hydrogen and C 1 -C 6 alkyl, and where R 12 is selected from hydrogen and C 1 -C 6 alkyl； R 1 is selected from hydrogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, -NR(R 13 ) 2 and -N(R 12 )-COR 14 ； where R 12 and R 13 are as defined above, and where R 14 is selected from hydrogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy and -NR 12 ； R 2 is selected from hydrogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, -N(R 13 ) 2 and -N(R 12 )-COCHR 2a R 2b ； where R 2a and R 2b are selected from hydrogen, hydroxy, C 1 -C 6 alkyl, C 1 -C 6 alkoxy, -N(R 13 ) 2 and -N(R 12 )-COR 14 ； where R 12 , R 13 and R 14 are as defined above； R 3 , R 4 and R 5 are independently selected from hydrogen, C 1 -C 6 alkyl and ± side chains of ±-amino acids or their enantiomers or their derivatives； R 6 is -CO 2 R 15 , -CONHR 16 , -CONHOR 16 , -CONHNHR 16 , -SO 2 N(R 16 ) 2 , -SO 2 R 17 or -P(O)(OR 18 )(OR 18 ) where each R 15 , R 16 , R 17 and R 18 is independently selected from hydrogen, C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, C 6 -C 10 aryl and C 7 -C 10 arylalkyl； B is an ±-amino acid residue, a ²-amino acid residue or an ±,±-disubstituted amino acid residue, such residue forming amide linkages with the adjacent molecules； W is -O- or CR 10 R 11 where R 10 and R 11 are as defined above； Y is an optionally substituted amino group, a moiety containing an optionally substituted amino group or a salt thereof: ---
