Fluorinated alpha-Amino Acid Analogues of L-Methionine and Related Compounds for Use As Potential Enzyme Inhibitors

Johnson, Bernadette (1998) Fluorinated alpha-Amino Acid Analogues of L-Methionine and Related Compounds for Use As Potential Enzyme Inhibitors. PhD thesis, University of Glasgow.

Abstract

With the discovery of AIDS (and the HIV virus) in the 1970's it has become increasingly apparent that AIDS and other immuno-compromised patients are particularly vulnerable to viral and fungal infections. If left untreated these infections which may only cause minor discomfort in a healthy individual can ultimately lead to the death of the immuno-compromised patient. The disease trichomoniasis found in humans and caused by the anaerobic flagellate protozoa Trichomonas vaginalis is one such infection. In the past trichomonal infections, including trichomoniasis, have been treated using 5-nitroimidazoles. However these agents can give rise to resistant strains of the parasite and are suspected of having mutagenic effects. The drawbacks of these existing treatments demonstrate the need to identify new pro-drugs of greater specificity towards the disease processes of viral and fungal infections. In the case of the organism Trichomonas vaginalis, we already know that the organism contains the enzyme L-methionine-gamma-lyase and that this enzyme performs a function peculiar to T vaginalis. This peculiarity is a potential source of increased specificity for this organism's particular disease process and as such the enzyme L-methionine-gamma-lyase presents itself as a target for therapeutic attack. If the suggested role of the enzyme is correct, then specific inhibitors of L-methionine-gamma-lyase could significantly reduce or even cure the pathogenicity of T vaginalis. In recent years a large number of compounds have been found to function as enzyme activated suicide substrates, through loss of a halide or other good leaving group. The vigorous development of organofluorine chemistry together with further advances in the understanding of biochemical processes have led to an increased level of interest and research in the area of fluorine containing aminoacids. Many fluorinated amino acids are now proving to be highly selective inhibitors of pyridoxal-5'-phosphate dependent enzymes. Following a rational drug design (RDD) approach, it was our aim to synthesise potential anti-metabolites for the therapeutic treatment of infections arising from anaerobic micro-organisms and helminths, in particular focusing our attention on the treatment of infections arising from the anaerobic flagellate protozoa T. vaginalis. The sulfur containing amino acid L-methionine plays diverse biochemical and physiological roles not only as a constituent of peptides and proteins but also as a precursor in the biosynthesis of the DNA methylating agent 5-adenosylmethionine. In addition to its importance in both biochemical and physiological processes, L-methionine is a natural substrate for L-methionine-gamma-lyase. Our experimental starting point has been to try to exploit this enzyme- substrate binding specificity. To do this we synthesised and biologically tested fluorinated analogues of L-methionine for growth inhibiting properties and or selective toxicity in T. vaginalis, an organism known to contain L-methionine-gamma-lyase. In addition and for comparison with L-trifluoromethionine we undertook to synthesise and biologically test the trifluoromethyl analogues of L-cysteine and D-penicillamine. In an alternative attempt to identify a selectively toxic compound for T. vaginalis we also explored a mechanism based enzyme inactivation approach involving the 2,3-sigmatropic rearrangement of an allyl sulfoxide to an allyl sulfenate ester in the enzyme active site. Via this approach the allyl sulfenate ester situated in the enzyme active site serves to derivatise and deactivate the target enzyme. This approach required the synthesis of 2-amino-4-chloro-5-(p-tolylsulfinyl) pentanoic acid from allylglycine. In an effort to extend our chemical and biological understanding of this alternative approach we also attempted to synthesise analogous chloro, fluoromethyl (sulfinyl) pentanoic acid compounds. It was hoped that these new compounds would create more favourable equilibrium concentrations of the sulfenate ester in the active site and that the presence of fluorine would convey an increased level of toxicity through improved lipophilicity and susceptibility to nucleophilic attack.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Ernest W Colvin
• Keywords: Biochemistry
• Date of Award: 1998
• Depositing User: Enlighten Team
• Unique ID: glathesis:1998-75885
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 17:40
• Last Modified: 19 Nov 2019 17:40
• URI: https://theses.gla.ac.uk/id/eprint/75885