A glycopeptide of the formula S-L-X--P, wherein: S is selected from an optionally protected monosaccharide, an optionally protected polysaccharide, a polyalkylene oxide chain and a group of the formula II, wherein R.sub.1 and R.sub.3 are independently selected from H or Ac, R.sub.4 is Ac, and R.sub.2 is a group of formula IV, wherein R.sub.7 and R.sub.8 are each independently selected from an optionally protected monosaccharide and an optionally protected polysaccharide, A, B, C and D are each independently 1 or 2, and m is 1 to 5; -L- is a moiety of the formula III wherein R.sub.5 and R.sub.6 are independently selected from H and Me and n is 1 to 3; and P is a peptide chain containing at least one amino acid having on its side chain the atom X, wherein X is an oxygen, a sulphur atom or a --CH.sub.2-- moiety.