Design, synthesis, conformational analysis, and biological activity of Cα¹-to-Cα⁶ 1,4- and 4,1-disubstituted 1H-[1,2,3]triazol-1-yl-bridged oxytocin analogues

Abstract

Oxytocin (OT) is a neurohypophyseal peptide hormone containing a disulphide-bridged pseudocyclic conformation. The biomedical use of OT peptides is limited amongst others by disadvantageous pharmacokinetic parameters. To increase the stability of OT by replacing the disulphide bridge with the stable and more rigid [1,2,3]triazol-1-yl moiety, we employed the Cu²⁺-catalysed side chain-to-side chain azide-alkyne 1,3-cycloaddition. Here we report the design, synthesis, conformational analysis, and in vitro pharmacological activity of a homologous series of Cα¹-to-Cα⁶ side chain-to-side chain [1,2,3]triazol-1-yl-containing OT analogues differing in the length of the bridge, location, and orientation of the linking moiety. Exploiting this macrocyclisation approach, it was possible to generate a systematic series of compounds providing interesting insight into the structure-conformation-function relationship of OT. Most analogues were able to adopt similar conformation to endogenous OT in water, namely, a type I β-turn. This approach may in the future generate stabilised pharmacological peptide tools to advance understanding of OT physiology.

Graphical Abstract

Keywords:

• Oxytocin
• β-turn conformation
• disulphide replacement
• intramolecular macrocyclisation
• CuAAC

Acknowledgements

AS is a participant of BioTechNan project - Interdisciplinary Environmental Doctoral Studies KNOW in the field of Biotechnology and Nanotechnology, cofinanced by the European Union. The PhD of AS was performed in the context of a Cotutorate between the PhD Schools in Chemical Sciences of the University of Florence (XXXV Ciclo) and of the Wroclaw University of Science and Technology. A.M.P. thanks Ms. Thi Hong Ha Nguyen for her technical support in peptide synthesis and purification.

Author contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. FN, LM and AS synthesised the building blocks and linear peptides and performed the CuAAC cyclisation; AS, ML, OL and RL recorded the NMR and CD spectra; MES collected the selected serum; ML and OL interpreted the NMR data and performed conformational analysis; BR, NT and CWG carried out and analysed the pharmacological assays, AMP, CWG, MC and PR developed the project, designed the experiments and analysed all data. All authors participated in interpretation of their experimental data.

Disclosure statement

The authors report no conflicts of interest.

Additional information

Funding

Work in the laboratory of CWG has been supported by the Austrian Science Fund (FWF, P32109).