A conjugate, wherein said conjugate is - a product of interest Y selected from the group consisting of glycoproteins, nanoparticles and labels for medical imaging, conjugated via a linker L with - a compound having the formula wherein - the dotted line represents a bond which is present or not, - X represents an analogue of a phosphate group, - R is selected from the group consisting of H and OH, - A is selected from the group consisting of O, S and CH 2, and wherein - said compound having the formula is linked to the linker via the A moiety, - said linker L separates A and Y by a chain of 4 to 15 consecutive atoms, when said bond represented by the doted line is not present, X is selected from the group consisting of: o a saturated phosphonate group having the formula o a bis-fluoro phosphonate group having the formula o a fluoro phosphonate group having the formula o a saturated carboxylate group having the formula and o a malonate group having the formula - when said bond represented by the dotted line is present, X is selected from the group consisting of: o an unsaturated phosphonate group having the formula and o an unsaturated carboxylate group having the formula - a product of interest Y selected from the group consisting of glycoproteins, nanoparticles and labels for medical imaging, conjugated via a linker L with - a compound having the formula wherein - the dotted line represents a bond which is present or not, - X represents an analogue of a phosphate group, - R is selected from the group consisting of H and OH, - A is selected from the group consisting of O, S and CH 2, and wherein - said compound having the formula is linked to the linker via the A moiety, - said linker L separates A and Y by a chain of 4 to 15 consecutive atoms, when said bond represented by the doted line is not present, X is selected from the group consisting of: o a saturated phosphonate group having the formula o a bis-fluoro phosphonate group having the formula o a fluoro phosphonate group having the formula o a saturated carboxylate group having the formula and o a malonate group having the formula - when said bond represented by the dotted line is present, X is selected from the group consisting of: o an unsaturated phosphonate group having the formula and o an unsaturated carboxylate group having the formula - the dotted line represents a bond which is present or not, - X represents an analogue of a phosphate group, - R is selected from the group consisting of H and OH, - A is selected from the group consisting of O, S and CH 2, - said compound having the formula is linked to the linker via the A moiety, - said linker L separates A and Y by a chain of 4 to 15 consecutive atoms, when said bond represented by the doted line is not present, X is selected from the group consisting of: o a saturated phosphonate group having the formula o a bis-fluoro phosphonate group having the formula o a fluoro phosphonate group having the formula o a saturated carboxylate group having the formula and o a malonate group having the formula o a saturated phosphonate group having the formula o a bis-fluoro phosphonate group having the formula o a fluoro phosphonate group having the formula o a saturated carboxylate group having the formula and o a malonate group having the formula - when said bond represented by the dotted line is present, X is selected from the group consisting of: o an unsaturated phosphonate group having the formula and o an unsaturated carboxylate group having the formula o an unsaturated phosphonate group having the formula and o an unsaturated carboxylate group having the formula