Synthesis and study of antibiotic cyclopeptides

Abstract

There is currently an important clinical worldwide challenge around the infections produced by multidrug-resistant bacteria. The discovery of effective antibiotics has diminished a lot in recent years, evidencing a great threat and an urgent need of new and safer antibiotics with broader spectrum to fight against these bacteria. A new field of study consists in reconsidering polymyxin, a cyclopeptide that presents excellent antimicrobial activity against Gram-negative bacteria. However, its use has been reduced over the years due to their neuro and nephrotoxicity, so that they are currently used only as a last resort antibiotic. As a consequence, one of the research areas consists in the synthesis of polymyxin analogs with the aim of improving its biological activity and reducing its toxicity. Regarding this work, three polymyxin analogs are firstly synthesized by solid phase peptide synthesis using Fmoc/tBu orthogonal protection strategy. Secondly, cyclization is carried out by the oxidation between two cysteine residues and finally, the analogs obtained are characterized by using RP-HPLC and ESI mass spectrometry. Moderately good yields and high purity are obtained for the analogs synthetized. Subsequently, the microbiological activity of the analogs is evaluated by determining their minimum inhibitory concentration (MIC) and, later, their hemolytic activity is studied as a toxicity test