the invention relates to a method of synthesis of a biopolymer derivative , preferably a chitosan derivative , comprising the formation of a peptide bond . the invention also relates to the biopolymer derivative , and use of the biopolymer derivative , preferably a chitosan derivative . the biopolymer derivative has broad uses in the industry , environmental protection and can be used in pharmaceutical and cosmetic compositions . the invention also relates to a composition for prevention of symptoms of allergy caused by heavy metals , especially palladium , cobalt , chromium and gold , in particular nickel .