Separation and identification of peptide mixtures in a synthesis crude of carbetocin by liquid chromatography/electrospray ionization mass spectrometry

In order to separate and characterize the target peptide and the side-product peptide compounds of a synthesis crude of the peptide hormone carbetocin, liquid chromatography coupled to high-flow electrospray ionization mass spectrometry (LC/eS-MS) has been used. Carbetocin is an important drug with recognized therapeutical application for stimulation of uterine contractions to facilitate parturition. Stepwise solid phase peptide synthesis (SPPS) commonly results in unwanted side products associated with incomplete peptide chains. Consequently, this procedure requires extensive purification and characterization of the final synthesis crude. The linear solvation energy relationship (LSER) method has been applied to optimize the proportion of organic modifier of the mobile phase used in the established LC method. On the other hand, ES-MS has allowed rapid and reliable identification of the target peptide and the other impurities present in the carbetocin synthesis products.

Solid-phase synthesis and biological activity of the parallel dimer of deamino-oxytocin

The parallel dimer of deamino-oxytocin has been synthesized by a novel solid-phase route. Successive orthogonal deprotection and oxidation reactions, carried out while the peptide remained anchored to a polymeric support, resulted in the formation of two disulfide bridges and conversion, with minimal side reactions, of the linear monomeric precursor to the dimer. The purified dimer showed approximately 0.1% to 2% of the biological activities of the monomer, as well as prolonged action. The time course of response to the deamino-oxytocin dimer differed from that of the monomer (and of oxytocin), and is probably due to slow formation of monomer under the conditions of biological testing.

Conformationally biased analogs of oxytocin

Four diastereomeric analogs of oxytocin containing substituted phenylalanine in position 2 were synthesized. This modified phenylalanine side chain contained one methyl group attached to the beta-carbon and the second one at the 2' position of the aromatic ring. All analogs were found to be inhibitors of uterotonic activity of oxytocin with pA2 values ranging from 6.0 to 8.3; the most potent one (pA2 = 8.3) contained dimethylphenylalanine of the D-erythro configuration.

Synthesis and some pharmacological properties of [4-threonine,7-sarcosine]oxytocin, a peptide with high oxytocic potency, and of [4-threonine,7-N-methylalanine]oxytocin

Two analogues of oxytocin, [Thr4,Sar7]- and [Thr4,MeAla7]oxytocin, were synthesized and their pharmacological properties investigated. [Thr4,Sar7]oxytocin was found to exhibit high biological activity (uterotonic activity of 1174 +/- 104 and milk ejection activity of 731 +/- 57 units/mg) and high selectivity for oxytocin-like relative to vasopressin-like activities (antidiuretic activity of 0.037 +/- 0.012 unit/mg, undetectable pressor activity). [Thr4,MeAla7]oxytocin was characterized by markedly lower biological activities. In both analogues, the additivity of the effects of the residues in positions 4 and 7 of oxytocin on the biological activity of the analogues was ascertained.

Effect of changing the COOH-terminal amide group present in the hydrophilic cluster of oxytocin to dimethylamide

Oxytocinoic acid dimethylamide was synthesized by stepwise solution techniques as part of an ongoing evaluation of the effects on the biological activity of oxytocin caused by individually changing the groups that comprises the hydrophilic surface of the hormone to more hydrophobic and more bulky groups. The analogue exhibited approximately 3% of the potency of oxytocin in the in vitro uterotonic assay. In addition, it possesses potencies of less than 0.07, less than 0.01, and 0.096 unit/mg in the avian vasodepressor, rat pressor, and rat antidiuretic assays, respectively. In the in vitro uterotonic assay, oxytocinoic acid dimethylamide showed a reduced affinity for the oxytocin receptor, a nonparallel dose-response relationship, and most importantly a reduced intrinsic activity as compared to oxytocin. The results suggest that the replacement of the protons of the primary carboxyamide of Gly9-NH2 of oxytocin by methyl groups displaces the active elements from the orientation for obtaining maximal intrinsic activity in the isolated rat uterus.

Combined high oxytocic with negligible antidiuretic and pressor activities in multisubstituted oxytocins

Oxytocin analogues which combine high oxytocic activities with negligible antidiuretic and pressor activities have been studied. [4-Threonine,7-glycine]oxytocin, [1-(L-2-hydroxy-3-mercaptopropionic acid),4-threonine,7-glycine]oxytocin, and [1-(L-2-hydroxy-3-mercaptopropionic acid)]oxytocin were found to possess the following specific biological activities respectively: rat uterotonic, 270 +/- 10, 337 +/- 23, 1542 +/- 0.4; rat antidiuretic, 0.002 +/- 0.0008, 0.048 +/- 0.005, 40.3 +/- 2.4. The results are analyzed from a conformation-activity viewpoint in a continued attempt to evaluate the scope and limitations of this approach in comparison to structure-activity studies.

Synthesis and some pharmacological properties of [1-(L-2-hydroxy-3-mercaptopropanoic acid), 4-threonine]oxytocin (hydroxy [4-thr]oxytocin), a peptide with strikingly high oxytocic potency and of [1-(L-2-hydroxy-3-mercaptopropanoic acid)]oxytocin (hydroxy-oxytocin)

[1-(L-2-Hydroxy-3-mercaptopropanoic acid), 4-threonine]oxytocin (hydroxy[4-Thr]oxytocin) and [1-(l-2-hydroxy-3-mercaptopropanoic acid)]oxytocin (hydroxy-oxytocin) were synthesized by a combination of solid phase and classical methods of peptide synthesis. Protected octapeptides were synthesized by the solid-phase method and 1 + 8 couplings in solution were then employed to furnish the required key protected intermediates. Hydroxy[4-Thr]oxytocin has oxytocic potency as measured in the rat uterus suspended in a Mg2+-free solution, of about 4200 units/mg, eight times the potency of oxytocin, while its antidiuretic potency is approximately equal to that of oxytocin. It thus exhibits a significantly favorable oxytocic-antidiuretic sleectivity. Hydroxy-oxytocin has an oxytocic potency of approximatels 1300 units/mt, 2.5 times that of oxytocin. Threonine substitution in hydroxy-oxytocin has thus caused a significant enhancement in both oxytocic potency and selectivity. The enhancement in oxytocic potency of these two peptides relative to oxytocin and [4-Thr]oxytocin appears to correlate with their lipophilic characteristics, suggesting a significant role of lipophilicity in the interplay of oxytocin-like peptides with oxytocic receptors.

Alkylating analogs of bradykinin

Three analogs of bradykinin have been synthesized which bear a bromoacetyl function on the alpha-amino group or on an anilinic amino group at position 5 or 8. It was hoped that one or more of these analogs might act as an irreversible bradykinin antagonist or as a long-acting converting enzyme inhibitor. Although none of the analogs exhibited the desired pharmacological properties, the methods described for the synthesis and characterization of peptides bearing anilinic bromoacetyl groups are of potential utility in the development of antagonists of other tyrosine--or phenylalanine--containing peptides.