Studies on Peptides. CXXXIX. : Solution Synthesis of a 42-Residue Peptide Corresponding to the Entire Amino Acid Sequence of Human Glucose-Dependent Insulinotropic Polypeptide (GIP)

Eight peptide fragments were prepared by known amide-forming reactions as building blocks for the solution synthesis of the dotetracontapeptide corresponding to the entire amino acid sequence of human intestinal GIP (gastric inhibitory polypeptide or glucose-dependent insulinotropic polypeptide). Besides Lys(Z), Trp(Mts) and Gln-OBzl, two new amino acid derivatives, Asp(OChp) and Glu(OChp) [Mts=mesitylenesulfonyl, Chp=cycloheptyl], were employed to suppress various side reactions. These fragments were successively assembled by the azide procedure to minimize racemization and all protecting groups employed were removed from the protected GIP by using 1M trifluoromethanesulfonic acid-thioanisole in trifluoroacetic acid.Synthetic GIP exhibited a significant glucose-dependent insulinotropic activity in dogs, but failed to produce any notable anti-gastric activity in rats.