1.Synthesis and chemical stability of a disulfide bond in a model cyclic pentapeptide: cyclo(1,4)-Cys-Gly-Phe-Cys-Gly-OH.
He HT1, Gürsoy RN, Kupczyk-Subotkowska L, Tian J, Williams T, Siahaan TJ. J Pharm Sci. 2006 Oct;95(10):2222-34.
Many cyclic peptides are formed using a disulfide bond to increase their conformational rigidity; this provides receptor selectivity and increased potency. However, degradation of the disulfide bond in formulation can lead to a loss of structural stability and biological activity of the peptide. Therefore, the objective of this study was to study the stability of peptide 1 (cyclo(1,4)-Cys-Gly-Phe-Cys-Gly-OH). This cyclic peptide was synthesized using Boc strategy via solution-phase peptide synthesis and purified using semi-preparative HPLC. The accelerated stability studies of the cyclic peptide were conducted in buffer solutions at pH 1.0-11.0 with controlled ionic strengths at 70 degrees C. The pH-rate profile shows that the peptide has an optimal stability around pH 3.0 with a V-shape between pH 1.0 and 5.0. Two small plateaus are observed at pH 5.0-7.0 and pH 8.0-10.0, indicating hydrolysis on different ionized forms of the cyclic peptide.
2.Kinetics of degradation and oil solubility of ester prodrugs of a model dipeptide (Gly-Phe).
Larsen SW1, Ankersen M, Larsen C. Eur J Pharm Sci. 2004 Aug;22(5):399-408.
Oil-based depot formulations may constitute a future delivery method for small peptides. Thus, a requirement is attainment of sufficient oil solubility for such active compounds. A model dipeptide (Gly-Phe) has been converted into lipophilic prodrugs by esterification at the C-terminal carboxylic acid group. The decomposition kinetics of octyl ester of Gly-Phe (IV) has been investigated at pH 7.4 (37 degrees C) and IV was shown to degrade by first-order kinetics via two parallel pathways (1) intramolecular aminolysis resulting in formation of a 2,5-diketopiperazine and (2) hydrolysis of the ester bond producing the dipeptide. The cyclisation reaction was dominating in the decomposition of methyl (II) butyl (III) octyl (IV) decyl (V) and dodecyl (VI) esters of Gly-Phe at pH 7.4. However, this degradation pathway was almost negligible for pH below 6. During degradation of the dipeptide esters in 80% human plasma pH 7.4 (37 degrees C) a minimal amount of cyclo(-Gly-Phe) was formed.
3.Dicarba analogues of the cyclic enkephalin peptides H-Tyr-c[D-Cys-Gly-Phe-D(or L)-Cys]NH(2) retain high opioid activity.
Berezowska I1, Chung NN, Lemieux C, Wilkes BC, Schiller PW. J Med Chem. 2007 Mar 22;50(6):1414-7. Epub 2007 Feb 22.
Dicarba analogues of the cyclic opioid peptides H-Tyr-c[d-Cys-Gly-Phe-d(or l)-Cys]NH2 were synthesized on solid phase by substituting allylglycines for the cysteines and cyclization by ring-closing metathesis between the side chains of the allylglycine residues. Mixtures of cis and trans isomers of the resulting olefinic peptides were obtained, and catalytic hydrogenation yielded the saturated -CH2-CH2- bridged peptides. The dicarba analogues retained high mu and delta agonist potencies. Remarkably, the trans isomer of H-Tyr-c[d-Allylgly-Gly-Phe-l-Allylgly]NH2 was a mu agonist/delta agonist with subnanomolar potency at both receptors.
