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.