title: Synthesis of two analogs of a cyclic hexapeptide with disulfide bridge corresponding to bovine prothrombin precursor sequence 18-23. Extent of carboxylation by Vitamin K-Dependent carboxylase.
abstract: The synthesis of two analogs of sequence 18-23 of bovine prothrombin precursor is described. Hexapeptides Boc-Cys (Acm)-Leu-Glu(OBzl)-Glu(OBzl)-Pro-Cys (Acm)-OBzl and Ac-Cys(Acm-Leu-Glu(OBzl)-Glu(OBzl)-Pro-Cys(Acm)-OMe were synthesized in solution by stepwise addition of Boc-amino acids using dicyclohexylcarbodiimide/N-hydroxybenzotriazole as the coupling reagent. The acetamidomethyl groups were cleaved and oxidized, using iodine in methanol, to the protected cyclic disulfide in 62-69% yield. The O-benzyl groups were removed either by treatment with anhydrous hydrogen fluoride or hydrogen bromide in trifluoroacetic acid to give the cyclic hexapeptide disulfides, R1-Cys-Leu-Glu-Glu-Pro-Cys-OR2 where R1 - H or Ac and R2 = H or CH3. The cyclic hexapeptides were evaluated as substrates for vitamin K-dependent carboxylase. Both peptides are unusually poor substrates for the carboxylase, and each appears to inhibit carboxylation of Phe-Leu-Glu-Glu-Leu, a good substrate for the enzyme.
mesh_terms: D000818:Animals; D015415:Biomarkers; D019735:Carbon-Carbon Ligases; D002417:Cattle; D004220:Disulfides; D008025:Ligases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000378:metabolism*; D011498:Protein Precursors; D011516:Prothrombin / Q000138:chemical synthesis / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014812:Vitamin K / Q000494:pharmacology
chemical_list: D015415:Biomarkers; D004220:Disulfides; D010446:Peptide Fragments; D011498:Protein Precursors; D014812:Vitamin K; C008208:acarboxyprothrombin; C033099:cysteinyl-leucyl-glutamyl-glutamyl-prolyl-cysteine cyclic disulfide; C033200:acetylcysteinyl-leucyl-glutamyl-glutamyl-prolyl-cysteine methyl ester cyclic disulfide; D011516:Prothrombin; D008025:Ligases; D019735:Carbon-Carbon Ligases; C020660:glutamyl carboxylase