A brief summary of the use of palladium as a catalyst, the characteristic reactivity of palladium complexes and the commonly used palladium-catalysed cross coupling reactions is given, with a special focus on the palladium-catalysed α-arylation of enolates and its application to the synthesis of aromatic heterocycles. The synthesis of aromatic heterocycles via both traditional methods and more recent metal-catalysed approaches is discussed in the context of isoquinolines. The palladium-catalysed oxidation of dihydrofurans bearing an ortho-bromophenyl group at the 2-position to the corresponding 2-phenyl furans is disclosed along with some preliminary mechanistic investigations. A novel synthetic route to isoquinolines is detailed involving the palladium-catalysed α-arylation of ketone enolates with an appropriate ortho-substituted aryl halide to furnish a protected 1,5-dicarbonyl intermediate. The versatility of these intermediates is demonstrated with their conversion into isoquinolines, isoquinoline N-oxides and naphthols. The scope of the synthetic procedure is fully exemplified across more than 30 different scaffolds covering the full spectrum of electron-rich to electron-deficient moieties. The intermediates were shown to be amenable to functionalisation with electrophiles, leading to isoquinolines bearing additional substitution at the C4 position. Sequential one-pot procedures were developed allowing three and four component couplings to directly deliver highly-substituted isoquinolines from commercially available starting materials. This methodology was utilised in the total synthesis of the natural product berberine in 26% overall yield and a longest linear sequence of six steps.

Peptides have attracted increasing attention as therapeutics in recent years, at least partially as a consequence of the widespread acceptance of protein therapeutics; but also as possible solutions to problems such as short half-life and delivery of molecules, and as therapeutics in their own right. The current work presents three projects that involve applications of peptides in a therapeutic environment. The first project studies the use of ER retaining peptides and CPPs (Cell penetrating peptides) in enhancing the effective concentration of DNJ (1-deoxynojirimycin), an α-glucosidase inhibitor, in cells. DNJ constructs with ER retaining peptides (6-[N-(1-deoxynojirimycino)]-hexanoyl-KDEL and 6-[N-(1-deoxynojirimycino)]-hexanoyl-KKAA) and CPPs (6-[N-(1-deoxynojirimycino)]-hexanoyl-TAT and 6-[N-(1-deoxynojirimycino)]-hexanoyl-MAP) were synthesised and analysed for their inhibitory activity against α-glucosidase I and II in vitro. The constructs were then analysed in a cell-based assay to determine their inhibitory activity on α¬-glucosidase-mediated hydrolysis of N-linked oligosaccharides. FITC-labelled ER retaining peptides were also synthesised to determine the internalisation and trafficking of the constructs by FACS and IF-microscopy. While none of the DNJ-constructs showed higher cellular inhibition than NB-DNJ (N-butyl DNJ; Miglustat), the CPP construct 6-[N-(1-deoxynojirimycino)]-hexanoyl-TAT showed comparable activity and the ER retaining construct 6-[N-(1-deoxynojirimycino)]-hexanoyl-KDEL showed a small but significant increase in activity following long-term administration. The second project focuses on beauveriolides, a cyclic depsipeptide family shown to have activity as ACAT inhibitors and thus a possible treatment for Alzheimer’s disease by the decrease in the production of Amyloid β (Aβ). A published total synthetic method was improved by the use of a cross-metathesis to reduce the total synthesis by 5 steps and increase its flexibility to allow the production of analogues. The synthesised beauveriolide III was used in attempts to develop an IF-FACS-based assay to measure the intracellular concentrations of Aβ. However, the location of γ-secretase in the used cell-line meant that levels of intracellular Aβ were not sufficient to track any decrease caused by ACAT inhibition. The third project involves the design of a cyclic peptide that could block the binding site for the influenza virus in the host cell. The cyclic peptide (cGSGRGYGRGWGVGA) was developed from a comparative study of four different sialic acid-binding proteins and synthesised by solution cyclisation of the linear peptide synthesised by traditional solid phase peptide synthesis (SPPS). An in silico study showed that the cyclic peptide allowed overlap with the binding site of Hemagglutinin. A 1H NMR titration determined the dissociation constant of the cyclic peptide to sialic acid. The KD corresponded to a low binding affinity, however the observed binding seemed to be specific and caused by a single bound conformation.

This thesis is concerned with the development of methodology for the asymmetric synthesis of a range of amino polyol containing compounds. Chapter 1 highlights the abundance of the amino polyol motif in nature, the wide range of biological activities displayed by amino polyol containing compounds, and their occurrence in drug molecules. A variety of different methods for the synthesis of stereodefined amino polyols is then discussed. Chapter 2 details a full investigation into the doubly diastereoselective conjugate addition reactions of the antipodes of lithium N-benzyl-N-(alpha-methylbenzyl)amide to enantiopurealpha,beta-unsaturated esters which contain a dioxolane unit. The “matched” conjugate addition reactions were further coupled with a highly diastereoselective in situ enolate oxidation using camphorsulfonyloxaziridine for the synthesis of keyalpha-hydroxy-beta-amino ester intermediates. Subsequent cyclisation and further elaboration allowed access to a range of amino polyol containing compounds including imino sugars, amino sugars, and amino acids. Chapter 3 extends the investigation into the doubly diastereoselective lithium amide conjugate addition reaction to enantiopure alpha,beta-unsaturated esters which contain two dioxolane units. A full assessment into the conjugate addition of the antipodes of lithium N-benzyl-N-(alpha-methylbenzyl)amide to a series of D-pentose derived alpha,beta-unsaturated esters is reported. Subsequent elaboration of thebeta-amino ester products of these conjugate addition reactions resulted in the synthesis of (2'S,3'S,4'R)-dihydroxyhomoproline and (2'S,3'R,4'S)-dihydroxyhomoproline. Chapter 4 describes the asymmetric syntheses of protected forms of APTO and AETD, the 2,4,5-trihydroxy substitutedbeta-amino acid residues found within the hexapeptide marine natural products microsclerodermins C, D and E. The optimised synthetic routes to APTO and AETD involved three key steps: a diastereoselective aminohydroxylation [via conjugate addition of lithium (R)-N-benzyl-N-(alpha-methylbenzyl)amide to an achiralalpha,beta-unsaturated ester followed by in situ enolate oxidation with camphorsulfonyloxaziridine], a diastereoselective dihydroxylation, and an olefination. Chapter 5 contains full experimental procedures and characterisation data for all compounds synthesised in chapters 2, 3 and 4.

Tunicamycins are potent antimicrobial agents but are also toxic to mammalian cells, which render them clinically impractical to use to treat infectious diseases. Instead, they have been used extensively as biochemical tools to study the N-linked glycosylation of proteins. However, despite such a routine application, their inhibitory mechanisms are still not clear. The central objective of this thesis was to develop novel tunicamycin analogues that are non-toxic to eukaryotic cells that could serve as potential antimicrobial drug candidates. We hypothesised that if we retain the lipid character of tunicamycin structure and modify the GlcNAc moiety then the antimicrobial activity would be retained but the tunicamycins inhibitory action towards GPT would be abolished, thus diminishing tunicamycins cytotoxicity towards mammalian cells. <b>I - Semi-synthesis of the Tunicamycin Core Scaffolds and Lipid Analogues</b> Semi-synthetic strategies were devised for isolating tunicamycin core scaffolds and for the selective addition of lipid chains at the 10'-N and 2"-N positions of tunicamycin, yielding the first library of novel tunicamycin lipid analogues. <b>II - Biological Evaluations of the Tunicamycin Core Scaffolds and Lipid Analogues</b> For the first time, the antibacterial activity of tunicamycins was shown to be dependent on the presence of a lipid chain. The tunicamycin core scaffolds were shown to lack antibacterial activity and cytotoxicity. More importantly, the library of tunicamycin lipid analogues with lipid chain length from seven to twelve carbons showed titrated antibacterial activity profile. Furthermore, the tunicamycin lipid analogues were not only found to have potent antibacterial and anti-M. tuberculosis activities but were non-cytotoxic compared to tunicamycins. The relative therapeutic index calculated for the tunicamycin lipid analogues was up to several thousand folds more than tunicamycins. <b>III - Investigation of the tunB and tunF Knockout in the tun Gene Cluster</b> The tunB and tunF single knockout mutations were made in the tun gene cluster by PCR-targeting and then heterologously expressed in S. coelicolor. The tunB knockout successfully abolished tunicamycin biosynthesis and showed evidence by MS the first existence of exo-glycal intermediates in sugar biology, further supporting the discovery of TunA as a novel NDP-sugar 5,6-dehydrogenase. <b>IV - Investigation of the TunD and TunE Enzymatic Activities in Tunicamycin Biosynthetic Pathway</b> The recapitulation of TunD glycosyltransferase and TunE deacetylase activities in vitro were attempted. Recombinant TunD was refolded from insoluble TunD inclusion bodies, while TunE was isolated in small quantities. However, no TunD and TunE activities were found using proposed intermediates. The co-translation of the tun gene cluster and the formation of multi-protein complex are proposed to be involved in the tunicamycin biosynthesis.