utylpyrazine was prepared by cyclization of H-Phe-Leu-CH2Cl, followed by acetylation with acetic anhydride. This pyrazine derivative can react with amino groups of amino acids or peptides to produce acetyl amino acids or acetyl peptides without acetylation of hydroxy group of Tyr, Ser and Thr. Using this acetylating reagent, Ac-Tyr-Val-Ala-Asp-MCA, which is a specific substrate of the interleukin-I