A polysaccharide consisting of 2 to 100 units of monosaccharide bearing 2 to 100 units of the compound of claim 1, wherein R is CO (CH2) nCO X in which n is 3 to 8 and X is selected from the group consisting of asparagine, glutamin and lysine and Ri is CO (CH2) nCOX in which n is 2 to 14 and X is a bond attaching said compound to said polysaccharide.