Synthesis of antibiotic cyclopeptides

Abstract

For the time being bacterial resistance has become one of the most important problems for public health. A large number of microorganisms have been developed, by natural selection, random mutations that have caused many of the antibiotics used previously are no longer effective. Therefore there is an urgent need for new drugs which can control these resistant bacteria. Some cyclopeptides as polymyxin B and E (colistin) show good antibacterial activity against gram-negative resistant microorganisms. Even so, its administration is limited due to they can cause neuro and nephrotoxicity. In the present work the synthesis of three polymyxin analogs has been carried out, with the aim of improving the pharmacological activity of this cyclopeptide in gram-positive and negative bacteria, and additionally to reduce its toxicity when being administered. The analogs synthesis has been carried out by the solid phase peptide synthesis and the Fmoc/tBu strategy as amino acids protecting groups, and its cyclization has made by oxidation between two cysteine residues, forming a disulfide bond. The peptides obtained with high purity have been characterized by HPLC and ESI mass spectrometry. Moreover, the antibiotic activity of the synthesized analogs has been determined through its minimal inhibitory concentration (MIC). We obtained good results and good selectivity against gram-negative bacteria (0.25 – 2 μg/ml) and better activity than polymyxin against gram-positive bacteria.