Open Access Dissertation
Date of Award
David . Crich
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
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
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.
Pirrone, Michael Gabriel, "Influence Of Conformational Restriction On The Antibacterial Activity And Ribosomal Selectivity Of Aminoglycoside Antibiotics" (2020). Wayne State University Dissertations. 2368.