PROBLEM TO BE SOLVED: To provide an N-terminal derivative of a protein or peptide, the N-terminal derivative being useful for improving the pharmacokinetics and pharmacodynamics of proteins and peptides in order to address physical and chemical instability of the proteins.SOLUTION: The invention provides a method for producing an N-terminal derivative of a protein, wherein a polysaccharide having a sialic acid unit at the terminal at least, and preferably consisting of essentially only the sialic acid unit reacts in the N-terminal of the protein or peptide in an acidic aqueous solution, and produces the N-terminal derivative, and the N-terminal derivative is purified in an aqueous solution with a higher pH than the reaction condition.SELECTED DRAWING: None【課題】タンパク質の物理的及び化学的な不安定性に対処する、タンパク質及びペプチドの薬物動態及び薬力学を改善するのに有用である，タンパク質又はペプチドの、Ｎ末端誘導体の提供。【解決手段】少なくとも末端にシアル酸ユニットを有し、且つ好ましくは本質的にシアル酸ユニットのみから成るポリサッカライドが、酸性の水溶液中でタンパク質又はペプチドのＮ末端で反応し、Ｎ末端誘導体を生成させ、反応条件より高いｐＨの水溶液中で前記Ｎ末端誘導体を精製する、タンパク質のＮ末端誘導体を製造する方法。【選択図】なし
