Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Abstracted in Dissertation abstracts, v. 19 (1959) no. 12, p. 3116. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, March 2002. / Includes bibliographical references. Also available on the Internet.

The emergence of multidrug resistant strains of bacteria has resulted in the need for novel therapeutic agents. The ApoEdp peptide, derived from the receptor-binding region of the human apolipoprotein E, had previously been shown to have activity against herpes simplex viruses, human immunodeficiency virus and certain bacterial species. However, its antibacterial mode of action was not elucidated, therefore the present study aimed to determine this mechanism. The susceptibility of several different strains, including Pseudomonas aeruginosa, Staphylococcus aureus, Mycobacterium smegmatis, Staphylococcus epidermidis and Escherichia coli, to ApoEdp was investigated. No significant difference was observed between the minimal inhibitory concentrations (MICs) of ApoEdp against a range of Gram positive and Gram negative bacteria. The presence of E. coli K5 capsular polysaccharide in the growth medium led to a decrease in ApoEdp susceptibility of the non-capsulated E. coli MS101 DeltakfiC strain. Bacteria with non-functioning multidrug efflux pumps showed no difference in susceptibility. A mutation in the phoP gene of Salmonella enterica Serovar Typhimurium LT2, which regulates cell surface modifications led to an increase in ApoEdp susceptibility. Transmission electron microscopy (TEM) images showed changes in the membrane and internal structures of strains incubated with a minimal bactericidal concentration (MBC) of ApoEdp for 5 min. ApoEdp was able to depolarise the cytoplasmic membrane. The ability of ApoEdp to induce cell lysis was assessed by the release of β-galactosidase into the supernatant. There was no significant difference in the supernatant β-galactosidase levels of ApoEdp treated and unlysed cells. ApoEdp, however was able to form pores in artificial lipid bilayers and decrease intracellular ATP levels. The effect of ApoEdp on transcription and translation was determined using an in vitro transcription/translation system. Results showed that ApoEdp did not affect protein synthesis. ApoEdp also worked in synergy with rifampicin, chloramphenicol, ampicillin and ciprofloxacin against bacteria. Overall, the results showed that ApoEdp acts by targeting the cytoplasmic membrane, although it may also have intracellular targets. Its ability to work in combination with conventional antibiotics and antibacterial activity against a range of different bacteria species demonstrates its therapeutic potential.

This thesis describes research undertaken in peptidomimetic chemistry, concerned with stabilisation of peptide secondary structure. The first section describes the successful synthesis of two triazepinediones for potential application as cis prolyl mimetics and/or β-turn mimetics. The first triazepinedione 64, carrying an N-phenyl substituent, was subjected to reductive conditions in an unsuccessful attempt to generate a cis prolyl peptide. The second triazepinedione 72 was designed as a Gly-cw Pro-Phe peptidomimetic. Its synthesis proceeded in 8 steps, via a chiral a-hydrazino acid. Triazepinedione 72 was extended from both the N and C termini, demonstrating that it could be incorporated into a peptide. The second section describes the design and attempted synthesis of an N-terminal template for stabilisation of a-helical structure in an attached peptide. Preliminary efforts to produce a Pro-Pro-Ala macrocycle 91 and a Pro-Pro-Pro ether macrocycle 98 were unsuccessful. Attempts to synthesise a Pro-Pro-Pro thioether macrocycle 112 resulted in formation of a cyclic dimer 122. The formation of this dimer was proposed to be due to excessive steric hindrance in the transition state to cyclisation. Attempts to stabilise the desired folded transition state by α-methylation of proline residues or hydrogen bonding did not allow synthesis of any of the desired monomeric cyclic material. A monomeric cyclic compound was finally obtained by increasing the flexibility of the linear precursor, affording a Pro-(2R)-Ala-Pro thioether macrocycle 151. X-Ray crystallography and 2D NMR studies established that this macrocycle lacked the required arrangement of carbonyl groups conducive to initiation of an α-helix. Further NMR studies of macrocycle-peptide conjugates suggested that the macrocycle exerted a conformational influence only over the first residue of the attached peptide. The carbonyl groups of the macrocycle were found to adopt a significant degree of α-helical geometry upon attachment of a C-terminal cationic trialkylammonium group.

D.Sc. (Chemistry) / Please refer to full text to view abstract

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A number of peptide intermediates and derivatives have been synthesized from both optically-pure and racemic amino acids. Carbobenzoxy-DL-alanyl chloride was coupled with L-leucine methyl ester and the mixed, crystalline carbobenzoxy-DL-alanyl-L-leucine methyl ester was isolated. Carbobenzoxy-DL phenylalanyl chloride and carbobenzoxy-DL phenylalanyl azide were coupled with L-leucine methyl ester and two products were separated by fractional crystallization. One of the products has been identified as carbobenzoxy-L-phenylalanyl-L-leucine methyl ester. A series of synthetic, dipeptide derivatives, containing some of those peptide bonds (present in the phenylalanyl chain of insulin) that Sanger and coworkers (31,32) found to be split by pepsin, were subjected to the action of pepsin at pH 2.0 and at pH 4-0. Proteolysis was detected by paper chromatography of the enzyme-substrate solutions. Of the compounds tested, carbobenzoxy-DL-phenylalanyl-DL-phenylalanine ethyl ester and carbobenzoxy-DL-phenylalanyl-L-tyrosine methyl ester were found to be hydrolysed by pepsin at pH 2.0 but not at pH 4.0. Synthetic compounds containing the peptide bonds - phenylalanyl-valyl, leucyl-valyl, glutamyl-alanyl, alanyl-leucyl, and glycyl-phenylalanyl -were resistant to pepsin even though it had been found (31,32) that, in insulin, these peptide bonds were pepsin-sensitive. These results indicate that, in the case of pepsin, observations on the action of pepsin on synthetic, dipeptide-type substrates should not be used to predict, or to explain, the specificity of pepsin on proteins or on high molecular weight peptides. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

After establishing that, like types B and E toxins, type A botulinus toxin contains only one residue of cysteine per molecule, chemical modification studies were carried out showing that sulfhydryl-specific reagents like p-chloromercuribenzoate (PCMB) and N-(4-dimethyl-amino-3,5-dinitrophenyl) maleimide (DDPM) cause a marked decrease in toxicity. Types A, B and E toxins were reacted with DDPM and a labelled peptide was obtained from the tryptic digest of each of the toxins. The quantitative amino acid analyses of these three peptides were remarkably similar. Sequence analyses showed that a sequence ala-glu-ser-cys-ser-asp-ser is common to all three DDPS-peptides. Type B botulinus toxin does not enzymatically alter acetylcholine in order to cause flaccid paralysis. It is postulated that the three thiol-containing peptides isolated contain all or part of a postulated active site common to each of types A, B and E botulinus toxins. / Science, Faculty of / Microbiology and Immunology, Department of / Graduate