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In this thesis I examined the potential of Bio-Oligomers such as peptoids, peptides and aptamers, as therapeutic and diagnostic entities. Therapeutic Bio-Oligomers; A series of peptoid analogs have been designed and synthesised using solid phase synthesis. These peptoids have been subjected to biological evaluation to determine structure-activity relationships that define their antimicrobial activity. In total 13 peptoids were synthesised. Out of 13 different peptoids, only one peptoid called Tosyl-Octyl-Peptoid (TOP) demonstrated significant broad-spectrum bactericidal activity. TOP kills bacteria under non-dividing and dividing conditions. The Minimum Inhibitory Concentrations (MIC) values of TOP for S. epidermidis, E. coli and Klebsiella were 20 μM, whereas Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-sensitive Staphylococcus aureus (MSSA) were 40 μM. The highest MIC values were observed for Pseudomonas aeruginosa (PAO1) at 80 μM. The selectivity ratio (SR) or Therapeutic index (TI) was calculated, by dividing the 10% haemolysis activity (5 mM) by the median of the MIC (50 μM) yielding a TI for TOP as 100. This TI is well above previously reported peptidomimetics TI of around 20. TOP demonstrates selective bacterial killing in co-culture systems and intracellular bacterial killing activity. Diagnostic Bio-Oligomers; In the second part of my thesis, I investigated aptamer and peptide-based molecular probes to detect MRSA. As well as screening aptamers and peptide probes against whole MRSA, I over-expressed and purified PBP2A protein. This purified protein was used as a target for aptamer and peptide probes to detect MRSA. Two different aptamer libraries were initially screened for utility. In-vitro conditions for SELEX were optimised. Biopanning with a phage derived peptides was also performed. Target sequences for both methods were identified and chemically synthesised. Evaluation of fluorescently labelled sequences with flow cytometry and confocal imaging showed no specificity for MRSA detection with either method. The Bio-Oligomers and the in-vitro selection methodology require further refinement to improve diagnostic utility.

This thesis is concerned with the synthesis of chiral pyrrolidinone scaffolds as mimics of the natural product pramanicin, and the evaluation of their antibacterial properties for use towards the development of potential novel antibacterial lead compounds. Chapter 1 discusses the urgency of the antibiotic resistance problem as well as the current lack of new antibiotics in the drug pipeline. This dearth of new antibacterials is partly attributed to the combinatorial libraries used in the screening process which occupies a limited chemical space. By applying the natural product-inspired paradigm, it is hypothesised that a drug discovery process with a starting point based on a natural product, possessing intrinsic antibacterial properties, may provide insights to a novel class of antibacterials. Chapter 2 describes the synthesis of three different scaffolds of oxygenated pyrrolidinones via a common bicyclic intermediate synthesised from L-pyroglutamic acid. The use of a mild and facile epoxidation condition utilising H₂O₂/tertiary amine afforded the epoxypyrrolidinones. α-Hydroxylation with “Davis oxaziridine” and a Ru-mediated dihydroxylation gave 2-hydroxypyrrolidinones and 2,3-dihydroxypyrrolidinones respectively. In all cases, a pendant Weinreb amide was used to introduce a variety of side-chains onto the parent pyrrolidinones. The enantioselective oxygenation of these scaffolds was accomplished as a result of the chiral [3.3.0] bicyclic intermediate. Chapter 3 describes the attempted synthesis of oxygenated pyrrolidinones via tetramic acids. Although progress was thwarted by synthetic challenges discussed therein, a series of tetramic acids was synthesised. A synthetic sequence to install a 3-acyl moiety onto the parent tetramic acid core was accomplished via an O-acyl/C-acyl rearrangement using a series of carboxylic acids in the presence of excess DMAP. The use of a 3-acyltetramic acid with a pendant phosphorane permits a general synthetic route, compatible with a wide range of aldehydes, towards 3-enoyltetramic acids via Horner-Wadsworth-Emmons olefination. These tetramic acids are mimics of another class of bactericidal natural products which nonetheless allows the natural product-inspired paradigm to be investigated. Finally, an analysis of the antibacterial properties of the synthesised compounds is discussed in Chapter 4. A cellular hole-plate bioassay with E. coli and S. aureus was chosen to provide a rapid assessment for active compounds. A correlation between the physicochemical properties and the observed activities of these active compounds suggested possible chemical modifications which could be undertaken in the future to improve their activities.