Cholecystokinin (pancreozymin). Synthesis and properties of the N alpha-acetyl-derivative of cholecystokinin 27-33.

The acetyl-derivative of the biologically active C-terminal 7-peptide portion of cholecystokinin (CCK), N-acetyl-O-sulfate-L-tyrosyl-L-methionyl-glycyl-L-tryptophyl-L-methionyl-L-aspartyl-L-phenylalanine amide was prepared by the condensation of 2-peptide segments with 1-isobutyloxycarbonyl-2-isobutyloxy-1,2-dihydroquinoline as coupling reagent. The N-terminal residue, tyrosine was incorporated by the active ester method. The same 7-peptide was prepared also by stepwise chain-lengthening, starting with the C-terminal residue. The 9-fluorenylmethyloxycarbonyl group was applied for the protection of alpha-amino functions. In the release of amylase from acinar cells of the pancreas of guinea pigs, the acetyl-7-peptide amide was about 3 times more potent than CCK 27-33 and equal in potency to CCK 26-33. The new derivative strongly stimulated the contraction of the in situ guinea pig gall bladder.