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No description available.

Human African Trypanosomiasis (HAT), commonly known as Sleeping Sickness, is endemic in over 36 countries in sub-Saharan Africa. It is caused by the parasitic subspecies Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense, which is transmitted to humans by the tsetse fly. The World Health Organisation estimates that 0.5 million people are currently infected with the disease, with a further 60 million at risk. HAT is lethal if left untreated and there is no vaccine available. There are only four accessible drugs, which are all inadequate and highly toxic. Thus there is a vital need for novel anti-parasitic agents. Compounds interfering with polyamine biosynthesis or function have shown potential use as anti-cancer, anti-HIV, anti-fungal and antiparasitic agents. The overall aim of this work was to synthesise novel macrocyclic polyamines containing different substituents to increase the toxicity against T. brucei. Twenty racemic substituted tetraazamacrocycles B have been synthesised using an iron template method in good yields (54-100%) from triethylenetetraamine and aromatic glyoxal derivatives A. The R-groups were aromatic or heteroaromatic and were selected to give compounds with varying electronic demand and a broad range of log P values. Two derivatives contain parasite-specific recognition motifs were also prepared. The compounds were tested against T. brucei and several of the analogues displayed high activity. Some of these azamacrocycles were also tested for activity against the malarial parasite Plasmodium falciparum, and for oligopeptidase B (OPB) inhibition, with a number of compounds exhibiting promising results.

This thesis describes the elucidation and comparison of substrate recognition relationships for the H2 nucleobase transporter of T. b. brucei and the main nucleobase transporter of human erythrocytes. Using standard transport kinetics, application of the Cheng-Prusoff equation and a derivation of the Nernst equation, it was possible to determine the Gibbs free energy (DG°) for the interactions of purine analogues with each transporter, which allowed predictions about the nature of the interactions that are essential for uptake. A range of unusual tricyclic and "fleximer" purine analogues was also assayed for ability to interact with the various purine transporters in T. b. burcei and human erythrocytes. This provided further insights into the extent that the substrate-binding pocket can accommodate unusual and large substrates. Some of the purine analogues used for the substrate-recognition study also displayed limited trypanocidal activity in vitro. More importantly, these results provide a foundation for the design and development of purine nucleobase analogues with anti-trypanosomal action that are efficiently and selectively accumulated by the parasite. One of the main aims of the project was to clone and characterise nucleobase transporters from T. b. brucei. The initial functional complementation strategy in nucleobase-transport deficient trypanosomes proved unsuccessful due to the presence of an additional, previously uncharacterised purine transporter in the trypanosome selection background and other technical obstacles. Homology searching of the T. b. brucei genome database led to the identification of a sequence with substantial similarity to the Adenosine Transporter 1 (TbAT1) gene previously shown to be responsible for the P2 nucleoside transport activity. The AT-like sequence was cloned, functionally expressed in heterologous systems (Saccharomyces cerevisiae and Xenopus oocytes), and characterised as the high-affinity Nucleobase Transporter 1 (TbNBT1). This also marked the first time a nucleobase-specific transporter had been cloned and characterised from any protozoan.