Influence Of Conformational Restriction On The Antibacterial Activity And Ribosomal Selectivity Of Aminoglycoside Antibiotics
Year: 2020
Type: dissertation
Abstract: The ever-increasing threat posed by multidrug-resistant infectious bacteria necessitates the development of novel antibiotics. Aminoglycoside antibiotics are growing in interest due to their broad spectrum of activity, lack of known drug related allergies, low manufacturing cost, and their well-studied mechanism of action. The simplification of rational drug design due to the well-studied mechanism of action is the key to overcoming the issues presented by these drugs, namely ototoxicity and nephrotoxicity. A study of the effect of the conformation of the aminoglycoside ring I side chain is described wherein it was discovered that an increase in a particular conformation augments the antibacterioribosomal and antibacterial activity of paromomycin, as well as decreasing the toxicity to human ribosomes. Chapter one introduces the aminoglycoside antibiotics and describes advantages and disadvantages of their clinical use. Various resistance mechanisms arising from target 162 modification, altered transport, and aminoglycoside modifying enzymes are discussed as is the mechanism of bacterial inhibition and how this is related to toxicity in human cells. Chapter two describes the synthesis of paromomycin and neomycin derivatives alkylated at C-6’ with both the (R) and (S) configurations as well as NMR spectroscopic studies of the side chain conformation of these derivatives. These derivatives were subjected to cell free ribosomal translation assays using M. smegmatis ribosomes with decoding A-sites of the wild type, human mitochondrial, mutant human mitochondrial, and human cytosolic ribosomes, as well as to bacterial MIC assays using E. coli and ESKAPE pathogens. The (R) configuration results in a higher solution state population of the bound conformation resulting in higher activity than the equivalent modification with the (S) configuration, which reduces the population of the bound conformation in solution. Chapter three describes the synthesis of paromomycin derivatives where ring I was fused to an additional ring by bridging O-4’ and C-6’, such that the conformation of the C5-C6 bond is locked. Conformational analysis by NMR spectroscopy shows a progression from the preferred solution state conformation of the ring I side chain to the ideal bound conformation as a function of the size of the fused ring. These derivatives were subjected to the cell free ribosomal assays and bacterial MIC assays. It was found that as the conformation of the locked side chain approached the ideal gauche, trans conformation the activity increased, leading to the conclusion that the gt conformation is the bound conformation. Chapter four discusses the effect of the 4’-substituent on the population of ring I side chain conformers in an attempt to rationalize the differences in activity between paromomycin, 4’-deoxy paromomycin, and 4’-deoxy-4’-propyl paromomycin (propylamycin), a recently 163 published synthetic aminoglycoside demonstrating equal activity to paromomycin and reduced toxicity in an animal model. Models of ring I of 4’-deoxy paromomycin and propylamycin were synthesized with and without selective deuteration at the side chain carbon. NMR spectroscopic studies of the relative populations of conformers of the ring I side chain for these models were conducted leading to the conclusion that the substituent at the 4’-position has minimal effect on the relative populations of the side chain conformers of ring I: any differences in activity between these compounds are due to other factors.
Source: Human Biology
Author: Michael G. Pirrone
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W3126967329