Abstract: A peptide comprising a unit of formula (I) and having a molecular weight of less than 2000 wherein each X is independently an organic group, e.g. a C1-6 alkyl or C1-6 alkenyl group, preferably —CH2—CH?CH2, or the two X groups taken together can form a covalent or non-covalent link between the two O groups, preferably a C1-10 saturated or unsaturated carbon chain optionally interrupted by one or more heteroatoms selected from O, S, N, P, or Si, especially a C3-10 carbon chain or one X represents an azido group and the other an C2-6-alkynyl group; both Z's are the same and are O or S; each Y is independently C, CH, CH2, N or NH; R1 is H or C1-6 alkyl; R2 is H or C1-6 alkyl; R5 is a C1-6 alkyl group, preferably isopropyl; or a salt, ester or prodrug thereof.

Abstract: A peptide comprising a unit of formula (I) and having a molecular weight of less than 2000 wherein each X is independently an organic group, e.g. a C1-6 alkyl or C1-6 alkenyl group, preferably —CH2—CH?CH2, or the two X groups taken together can form a covalent or non-covalent link between the two O groups, preferably a C1-10 saturated or unsaturated carbon chain optionally interrupted by one or more heteroatoms selected from O, S, N, P, or Si, especially a C3-10 carbon chain or one X represents an azido group and the other an C2-6-alkynyl group; both Z's are the same and are O or S; each Y is independently C, CH, CH2, N or NH; R1 is H or C1-6 alkyl; R2 is H or C1-6 alkyl; R5 is a C1-6 alkyl group, preferably isopropyl; or a salt, ester or prodrug thereof.