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Vitamin B12 (cobalamin) is one of Nature's most complex small molecules. It is a cobalt-containing modified tetrapyrrole that plays a number of key metabolic roles in many prokaryotic systems and is also essential to the biochemistry of higher animals. However, it is made by only certain bacteria, requiring around thirty enzymatic steps for its complete de novo construction. Surprisingly, the nutrient is synthesised by one of two related, though genetically distinct, pathways that represent aerobic or anaerobic routes. The anaerobic pathway has remained poorly characterised due to the instability of the pathway intermediates to oxygen and the low activity of enzymes, and is the focus of the research reported in this thesis. The Gram-positive aerobe Bacillus megaterium has previously been used for the commercial production of cobalamin and has a complete anaerobic pathway. Several genes, (termed chi for 9,obinamide biosynthesis) from the cobalamin biosynthetic pathway have been cloned and overexpressed individually within the host B. megaterium DSM319. One of the major bottlenecks in the anaerobic pathway is the ring contraction step, where only limited yields « 5 %) of product had previously been obtained using crude-lysate based incubations. By studying the purified B. megaterium CbiH60 enzyme, an efficient method was developed to allow the generation of the ring-contracted product cobalt-factor IV in high yields. This breakthrough then permitted the characterisation of many of the down-stream steps in the pathway to be characterised by using other purified cobalamin biosynthetic enzymes from B. megaterium, by incubating combinations of purified enzymes with cobalt-factor IV and the appropriate cofactors (SAM, NADH). This has resulted in the successful step-by-step elucidation of the anaerobic cobalamin pathway, including the isolation of the long sought-after and elusive intermediates cobaltprecorrin- 5, -6A, -6B, -7 and -8. An enzyme-cocktail approach has also resulted in a full in vitro synthesis of cobyrinic acid (the first known stable intermediate in the pathway) from 5-aminolevulinic acid has been demonstrated, involving a full 15 enzymatic steps. The exposition of the anaerobic pathway has been interpreted with respect to the chemical logic of the metabolic process and the evolution of multifaceted biochemical pathways.

Molecularly imprinted polymers (MIPs) are crosslinked polymers containing bespoke functionalised cavities arising from the inclusion of template molecules in the polymerisation mixture and their later extraction. When the polymers are prepared functional polymerisable monomers are included which become part of the polymer matrix and serve to decorate the cavities with functionality appropriate to the template molecules. Overall, binding sites are created which have a memory for the template both in terms of shape and matching functionality. Fluorescent molecularly imprinted polymers have the benefit of a fluorophore in their cavities that may respond to the presence of bound test compound by a change in their fluorescence output. The work presented falls into three main areas. A series of fluorescent MIPs was prepared with a view to generating material capable of mimicking the binding characteristics of the metabolically important cytochrome isoform CYP2D6. The MIPs re-bound their templates and various cross-reactivities were encountered for test compound/drug recognition. One MIP in particular exhibited a rational discrimination amongst the related synthetic templates and was reasonably successful in recognising CYP2D6 substrates from the drug set tested. In order to give some insights into binding modes in MIPs, attempts were made to produce functional monomers containing two or more fluorophores that could be interrogated independently. A model compound was prepared which fitted the dual-fluorophore criteria and which will be the basis for future incorporation into MIPs. A further strand to this thesis is the deliberate incorporation of hydrophobic moieties into fluorescent functional monomers so that the resulting imprinted cavities might be biomimetic in their impersonation of enzyme active sites. Thus the imprinted cavities had specific hydrophobic regions as well as the usual polar functionality with which to interact with binding test compounds.

Plus de la moitié des médicaments mis sur le marché entre 1981 et 2014 sont des produits naturels ou des dérivés. Ainsi, les structures des produits naturels sont une excellente source d'inspiration pour la découverte de nouveaux médicaments. L'introduction de cette thèse met en lumière le rôle important joué par les produits naturels en chimie médicinale. De plus, la préparation de produits naturels peut déboucher sur le développement de nouvelles méthodes de synthèse. Ainsi, au cours de cette thèse une approche synthétique de plusieurs produits naturels a été réalisée. Ces composés présentent des motifs clés tels que des amino-alcools 1,3, des diamines 1,3 ou un tétrahydropyrane. Les études synthétiques réalisées comprennent le développement de nouvelles méthodes pour accéder à ces structures. D'autre part, une réaction de Heck permettant l'accès à des précurseurs de tri-aryl éthylènes a été mise au point. / It has been estimated that more than half of all approved drugs, from the period 1981 to 2014, are either natural products or their derivatives. This, thus, indicates that natural products (NP), together with natural product derived and natural product inspired structures are significant as sources for potential leads towards the discovery of new drugs. The introduction of this thesis thereby highlights the importance of natural products in the field of drug discovery. In addition, the introduction emphasizes on the importance of natural products as a field of research. This is as the synthesis of natural products can result in the development of new synthetic methods which can then be applied to a broader range of applications across the field of chemistry. This new information, thus, bridges a gap in the scientific knowledge and allows for progress in science. Therefore the content of this thesis describes the syntheses and development of new synthetic methods towards bioactive natural products containing 1,3-amino alcohol, 1.3-diamine, THP-ring as well as tri-aryl ethylene unit which represent the key themes of (+)-negamycin (Chapter 1), (-)-cernuine and (+)-cermizine D (Chapter 2), enigmazole A (Chapter 3) and tamoxifen (Chapter 4), respectively.