Zur Synthese von Cholecystokinin-Pankreozymin. Darstellung von [28-Threonin, 31-Norleucin]- und [28-Threonin, 31-Leucin] Cholecystokinin-Pankreozymin-(25-33)-nonapeptid

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Abstract
The syntheses of 2 analogs related to the C-terminal nonapeptide amide sequence 25-33 of cholecystokinin-pancreozymin [CCK-PZ] are described. Based on the primary structure of the CCK-PZ-active cerulein and the experiences gained from the methionine replacement with leucine or norleucine in human little gastrin I, the analogs were designed by substituting methionine 28 with threonine, and methionine 31 with leucine and norleucine, respectively. Using a new method for the synthesis of tyrosine-O-sulfate-containing peptides and applying acid-labile side-chain protection in combination with the benzyloxycarbonyl group, the fully protected nonapeptide amide derivatives Z-Arg(Z2)-Asp(OBut)-Tyr-(SO3Ba1/2)-Thr(But)-Gly-Trp-Leu-Asp(OBut)-Phe-NH2 and Z-Arg(Z2)-Asp(OBut)-Tyr(SO3-Ba1/2)-Thr(But)-Gly-Trp-Nle-Asp(OBut)-Phe-NH2, were obtained. Upon hydrogenolytic and subsequent acidolytic removal of the protecting groups, followed by purification via chromatographic procedures the nonapeptide amides were isolated in satisfactory yields at a high degree of purity. In vivo and in vitro assays showed that a substitution of methionine 31 by norleucine with concomitant replacement of methionine 28 by threonine produced a fully active analog, whereas for the threonine 28, leucine 31 analog the pancreozymin-activity was lowered by a factor 10.