A polymeric compound comprising 2 to 100 units of Dglucosamine, each unit bearing a compound of formula II : wherein R2 is a hydrogen or acetyl and R3 is phenyl or tButyloxy and wherein R is CO (CH2) nCOX in which n is 2 to 14 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 the compound of formul