Synthesis and acid ionization constants of cyclic cystine peptides
- 12 January 2009
- journal article
- research article
- Published by Wiley in International Journal of Peptide and Protein Research
- Vol. 34 (4) , 346-351
- https://doi.org/10.1111/j.1399-3011.1989.tb01585.x
Abstract
Cyclic peptide disulfides of the general formula H-Cys-(Gly)n-Cys-OH (n = 0-4) were synthesized from the corresponding peptide derivatives [Boc-Cys(Trt)(Gly)n-Cys(Trt)-OBut] by oxidation with iodine in methanol and by subsequent removal of the terminal groups with trifluoroacetic acid. Acid ionization constants of the obtained peptides were determined by potentiometric titration in aqueous KC1 (0.1 mol/L) medium. All compounds have two dissociable hydrogens, corresponding to carboxyl (pK1 = 2.35-2.84) and to terminal amino group (pK2 = 5.61-6.93); pK1 values show first an upward and then a downward trend with the increase in ring size; the opposite is true for pK2 values. These trends could be tentatively attributed to the intramolecular salt bridge (-COO- ----NH3+-) formation.Keywords
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