Synthesis of the antimicrobial peptide murepavadin using novel coupling agents

The problem of antimicrobial resistance is becoming a daunting challenge for the human society and health care systems around the world. Hence, there is a constant need to develop new antibiotics to fight resistant bacteria, among other important social and economic measures. In this regard, murepavadin is a cyclic antibacterial peptide in development. The synthesis of murepavadin was undertaken in order to optimize the preparative protocol and scale-up. In our hands, classical approaches using carbodiimide/hydroxybenzotriazole rendered low yields. In addition, benzotriazole-based reagents have been reported to exhibit explosive properties. The use of the new TBEC carbodiimide and reagents based on OxymaPure^® and Oxy-B is discussed together with proper use of chromatographic conditions for the adequate characterization of the peptide crudes. Higher yields and purities are obtained with the new reagents compared to traditional protocols. Finally, the antimicrobial activity of the different synthetic batches was tested in three Pseudomonas aeruginosa strains, including highly resistant varieties which consisted of two carbapenem-resistant strains and an extended spectrum ß-lactamase (ESBL) producer. All murepavadin batches yielded the same MIC values, independently of the synthetic approach used, which demonstrates that the chiral integrity of the molecule was preserved throughout the whole synthetic procedure.