CLipPA Lipidation in the Synthesis of a New Generation of Polymyxin Analogues

Abstract

Since the discovery of penicillin and the years of research breakthroughs that followed, the development of antibiotics has significantly slowed in more recent decades.¹ The reasons of such decline are: (a) lack of interest from the pharmaceutical industry due to low profit;² (b) the rise of multi-drug resistant (MDR) bacteria.³ These bacteria contain antimicrobial resistant (AMR) characteristics, which are a threat to the global community.³ Peptide-based antibiotics have emerged as promising antimicrobial agents, especially lipopetides such as Polymyxin B (PMB).⁴̓, ⁵ Despite its nephrotoxicity, PMB is one of the last line antibiotics against Gram-negative bacterial infections. The structure of PMB, which consists of an N-terminal fatty acyl chain, an exocyclic tripeptide and a cyclic heptapeptide, allows for various substitutions and modifications to improve potency and reduce toxicity. This project seeks to develop new lipopeptide antibiotics that display potent antibacterial activity, and with a reduction in the unwanted side effects of PMB. Using a chemical process named CLipPA, a novel method to introduce lipids to peptides, in conjunction with Fmoc solid phase peptide synthesis (SPPS), a series of PMB analogues were generated for activity studies against Gram-negative bacteria. The current lead compound of the project is a PMB analogue with both its N-terminal fatty acyl chain and the D-Phe⁶ substituted with a lipidated cysteine containing a thioether linked phenyl group. Different lipidated substituents on the D-Phe6 position were explored, in order to understand the structure-activity relationship of these analogues. Biological evaluations of these analogues are currently in progress.