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Introduction: Intracranial aneurysms affect 2-5% of the general population.1 A tiny proportion of these rupture leading to aneurysmal subarachnoid haemorrhage (SAH), which can be fatal instantly or lead to life-changing neurological morbidity in a young group of stroke survivors. Understanding the pathophysiological mechanisms underlying intracranial aneurysms, and being able to predict which patients have a higher risk of rupture has led to intensive research efforts, via epidemiological, molecular and genetic studies. Our aim was to determine the association of candidate genes with intracranial aneurysms in a large UK Caucasian population. Methods: We performed a case-control genetic association study of single nucleotide polymorphisms (SNPs) in over 1600 patients with intracranial aneurysms from a UK-wide Genetic and Observational Subarachnoid Haemorrhage (GOSH) study and 1500 controls from the Wellcome cohort,2 utilising a candidate-gene approach. We conducted a literature review and performed a meta-analysis of the existing candidate gene studies to better determine which genes would be suitable for analysis in our cohort. We also performed a new meta-analysis using our data for each SNP examined to determine if our genetic associations with intracranial aneurysms were robust. Results: We examined 22 SNPs related to vascular endothelial integrity, the extracellular matrix, and inflammation. Two SNPs showed associations with intracranial aneurysms in our UK cohort: the D allele of ACE Insertion/Deletion SNP (associated with vascular endothelial function; OR 1.14 [1.02-1.28], p=0.02) and the MMP-2 C > T rs243865 SNP (associated with extracellular matrix integrity; OR 1.18 [1.04 - 1.33], p=0.012). Conclusions: We found associations with intracranial aneurysms for the D allele of the ACE I/D SNP, and a potentially functionally significant MMP-2 SNP. Both genes have plausible connections to IA pathophysiology (endothelial function and extracellular matrix integrity, respectively), and could potentially predispose patient to aneurysm rupture as demonstrated by sub-group analysis.

The work presented in this thesis aims to understand the role of the Sry-box transcription factor (SOX9) in liver fibrosis as a route to novel diagnostic strategies for the disease. Fibrosis of the liver is a major cause of morbidity and mortality in the UK characterised by progressive accumulation of extracellular matrix (ECM) proteins. End-stage disease is treated by transplantation, but this is limited by donor numbers. Although potentially reversible if diagnosed early, current methods of diagnosis are invasive and prone to sampling error. There is a critical need to improve current methods or develop novel strategies to determine fibrotic activity and disease progression. To address this, better mechanistic understanding of liver fibrosis is urgently required. My supervisor (Dr Piper Hanley) previously discovered ectopic expression of SOX9 as a novel mechanism to underlie aspects of liver fibrosis. This discovery allowed me to investigate the molecular genetic network in which SOX9 operates. Given SOX9’s seemingly central role, I identified novel target genes of SOX9 action, some of which have already been highlighted as candidate biomarkers, for new diagnostic strategies in liver fibrosis. Moreover, investigating the expression of SOX9 directly during liver fibrosis in human biopsy samples highlighted the factor as a prognostic marker of the disease. This thesis focussed on four key research areas: Identification of the inflammatory glycoprotein Osteopontin (OPN) as a direct target of SOX9. In addition to OPN, identification of four other downstream SOX9 targets as potential biomarkers of liver fibrosis severity. SOX9 expression in liver biopsies is described and quantified, highlighting its role as a new method to assess liver fibrosis progression. This work is being patented as a novel prognostic test in liver fibrosis. Finally, the role of SOX9 mediating ECM through inhibition of collagenases (e.g. MMP13) is described. Taken together, these data place SOX9 as a key mediator of liver fibrosis. However, translation of novel SOX9 targets as serum biomarkers of fibrosis and SOX9 as a marker of disease progression have ramifications on clinical practice, in particular assessing liver fibrosis progression.

Gap junctions (GJ) connect the cytoplasm of two adjacent cells and have two probable functions, synchronisation of networks by direct electrical communication and allowing. the passage of small molecules. This thesis examines the distribution patterns and physiological roles of the neuronal GJ sub unit connexin 36 (Cx36) in autonomic and respiratory control. Using the working heart brainstem preparation of the rat and mouse recordings were made during baseline and during peripheral chemoreceptor and baroreceptor stimulation. Central sympathetic drive was attenuated with the addition of 1 μM of mefloquine (M F) to the perfusate. MF (which blocks Cx36 containing GJs) induced a resting bradycardia, attenuated the amplitude of respiratory related sympathetic bursts, attenuated chemoreceptor-induced sympathoexcitation and increased heart rate recovery time after chemoreceptor stimulation. Attenuated respiratory responses to autonomic reflex stimulation were observed with MF, no significant alterations in baroreflex sensitivity were observed. Studies in Cx36 knockout mice were analogous to data obtained with MF. Telemetric probes inserted in free running wild type and Cx36 knockout mice which continually recorded heart rate and arterial pressure revealed significantly augmented variations in resting heart rate and arterial pressure in Cx36 knockout mice in comparison to wild type mice. Autonomic reflexes examined in anaesthetised Cx36 knockout mice revealed attenuated heart rate changes in response to chemoreceptor stimulation. Cx36 immunoreactivity and Cx36 cyan fluorescent protein expression was reported at various brainstem and spinal cord sites involved in autonomic function including, the nucleus of the solitary tract and sympathetic preganglionic neurones (SPNs). The results revealed that Cx36, at the level of the SPNs, plays important roles in regulating sympathetic outflow. This may have important clinical implications as an imbalance in the sympathetic and parasympathetic outflow to the heart for example, underlies various maladies from hypertension to cardiac arrhythmias

This thesis examined the effectiveness of an intensive, community-based intervention for youth presenting with complex psychological needs, and their families, and discussed the need to understand and address the multiple risk and protective factors across several systems associated with aggressive, violent, antisocial and offending behaviour in young people, in order to intervene effectively. The intervention is based on the principles of Multi-Systemic Therapy (MST), a renowned intensive, community-based intervention for aggressive, violent and antisocial young people, which is explored in the literature review (Chapter 1). The available evidence-base on MST demonstrates that the behaviour of young people considered at significant risk to themselves and/or others can be managed safely within the community, while engaging their caregivers and wider ecology to effect positive changes that are sustainable. The research study (Chapter 2) reports on a modest sample of 17 young people and 12 caregivers who completed research measures prior to and following the receipt of the intensive intervention based on MST principles aimed at improving youth and family functioning. Positive changes in both individual functioning and family environment observed were found to be consistent with the existing evidence-base regarding the effectiveness of community based interventions. This provides support for moving away from traditional office-based approaches to engaging these clients in order to prevent further deterioration in behaviour and subsequent placement of the young person away from his/her family and community. A discussion surrounding the use of psychometric measures provides insight into the role of the family environment in assessing and intervening with this client group in Chapter 3. Finally, the importance of recognising families as the key to a successful system of care is further explored in the case study in Chapter 4. Overall, this thesis provides support for the abandonment of a simplistic superficial understanding of social, emotional, and behavioural difficulties in young people to a more ecological, dynamic approach, which has implications for prevention of the detrimental and long lasting costs of youth social, emotional and behavioural difficulties.

The inherent strain of highly constrained ring systems has enabled their exploitation in organic synthesis for decades. However, methods utilising modern photoredox catalysis remain underexplored. The studies presented in this thesis detail efforts to employ highly strained rings in various strain-induced ring-opening and cyclisation sequences using visible light photocatalysis. Chapter 1 introduces and summarises previous efforts for [3+2] cycloadditions of cyclopropylamines, highlighting numerous inter- and intramolecular processes through both traditional and modern photoredox strategies. Most avenues utilise cyclopropylanilines and styrenes, limiting the potential for access to diverse products, and few examples exhibit high diastereoselectivity. In Chapter 2, studies towards the improvement of previous cycloaddition sequences are discussed. An operationally simple strategy employing N-sulfonyl cyclopropylamines is used, featuring facile oxidation of an aza-anion for accessing the key nitrogen-centered radical. The methodology enables access to sulfonyl-protected amino-cyclopentanes in high yields with excellent trans-selectivity. Various electron-deficient olefins are tolerated, and alteration of the sulfone substitution was also achieved. Analogues bearing fully substituted quaternary centres are obtained, however expansion onto the synthesis of highly functionalised products proved more challenging. Disubstituted olefins gave issues of poor diastero- or regiocontrol, and fused cyclopropylamine substrates were incompatible. Mechanistic investigations confirmed the key stereo-defining cyclisation step to be anionic in nature (rather than radical) in nature. Product derivatisations showcased the synthetic utility of the process and X-ray crystallography validated trans-selectivity. Chapter 3 introduces previously reported routes to access derivatives of the spiro[3.4]octane family, and highlights key reactions which employ electron-deficient bicyclobutanes (BCBs). In Chapter 4, studies towards the use of alkene-tethered BCBs in a photoredox-mediated spirocyclisation is discussed. The developed methodology permitted the modular construction of unique spirocycles in high yields and as a mixture of diastereomers, from a range of radical precursors and substituted BCBs. Incorporation of heteroatoms was tolerated in the cyclisation to afford rare aza- and oxospiro[3.4]octanes. Furthermore, novel scaffolds bearing adjacent spirocyclic centres were achieved. The successful exploitation of BCBs in the synthesis of spirocyclic compounds serves as an interesting foundation for future endeavours.

Lipopeptide natural products have garnered significant attention from the synthetic chemist due their potent biological activity against a range of targets. Aggarwal has developed a suite of synthetic methods leveraging boronic-ester homologation chemistry to construct these molecules efficiently. The macrolipopeptide dysoxylactam A, isolated and characterised in 2019 by Yue and co-workers, was synthesised in 11 steps. Key features of the synthesis are the utilisation of iterative lithiation-borylation reactions (assembly-line synthesis) for the construction of the stereochemically dense lipophilic portion of the molecule, the use of a single protecting group and a total of 5 chromatographic purifications. Other steps include a Steglich esterification, macrolactamisation and Fleming oxidation. The automated synthesis of (+)-kalkitoxin required starting with a thiazoline containing boronic ester, performing six automated iterative lithiation-borylation reactions, and then boronic ester amination, acylation and amide methylation. The boronic ester amination proved to be exceptionally challenging due to undesired isomerisation of the thiazoline ring. After extensive investigations into this transformation, a new boronic ester amination procedure was discovered, in which the reaction proceeds rapidly at room temperature. Although this method was unsuitable for the thiazoline containing boronic ester, it represents the mildest and simplest direct conversion of a boronic ester to an amine.

Despite the favourable properties that azetidine rings can engender drug-compounds with, methods for the modular synthesis of azetidine-based structures are significantly underexplored. This thesis outlines the development of several novel strategies that facilitate the assembly of functionalised azetidines and azetidine-containing spirocycles. Key to achieving these new modes of reactivity was the ability to harness the inherent strain energy of azabicyclo[1.1.0]butyl lithium (ABB-Li), which provides a strong thermodynamic driving force to access unexplored regions of chemical space. The essential criteria for these targeted protocols were that they must be operationally simple, tolerant of a broad range of functional groups, modular and must generate products with the potential for further elaboration. In this context, a unique approach toward the synthesis of azetidine-containing spirocycles was established through the development of an electrophile-induced spirocyclisation-desilylation reaction. This was achieved via the single step synthesis of ABB-ketone precursors bearing silyl-protected alcohols which could be effectively transformed into a library of new spiro azetidines, with a range of substituents and ring sizes. Building on this success, a novel strain-release-driven Friedel-Crafts spirocyclisation reaction of azabicyclo[1.1.0]butane-tethered (hetero)aryls was subsequently investigated. This reaction was discovered to proceed through an unexpected interrupted Friedel-Crafts mechanism, generating a highly complex azabicyclo[2.1.1]hexane scaffold. This dearomatised intermediate, formed exclusively as a single diastereomer, could be subsequently converted to the Friedel-Crafts product upon electrophilic activation of the tertiary amine, or trapped as a Diels-Alder adduct in one-pot. Finally, the successful realisation of a four-component [1,2]-Brook rearrangement/strain-release-driven anion relay sequence and its application to the modular synthesis of acyl azetidines is described. The rapidity of the reaction, as confirmed by in situ infra-red spectroscopy, leveraged the strain-release ring-opening of azabicyclo[1.1.0]butane to drive the equilibrium of the Brook rearrangement. These newly developed procedures demonstrate the potential of utilising strain-release as a synthetic strategy for the rapid assembly of sp3-rich heterocycles. The wider application of these reactivity regimes will open new vistas to access nitrogen-containing drug-like cores that can be easily diversified through the judicious choice of starting materials and further elaborated via the orthogonal manipulation of multiple functional handles.

Pyridines, dihydropyridines and piperidines are important components in bioactive compounds. Cyclobutanes and spirocycles are also attractive motifs in contemporary drug design due to their rigidity and well-defined shape. This thesis outlines investigations into novel methods of achieving sp2-sp3 cross-coupling to pyridines and achieving the synthesis of cyclobutyl boronic esters and dihydropyridine spirocycles. First, investigations into novel methods of achieving stereospecific sp2-sp3 cross-couplings to pyridines are discussed. A stereoinvertive cross-coupling at the C4-position of the pyridine ring was achieved by addition of a chiral boron-ate nucleophile to an N-acylpyridinium electrophile followed by rearomatisation of the dihydropyridine intermediate to the parent pyridine. A stereoretentive C2 cross-coupling of alpha-magnesiated pyridine N-oxides with boronic esters was also attempted, with the anticipation that electrophilic activation of the N-oxide moiety of the boron-ate intermediate would trigger a 1,2-metallate rearrangement and subsequent elimination/rearomatisation to give the cross-coupled pyridine. Secondly, contributions towards exploring the scope of a diastereoselective synthesis of cyclobutyl boronic esters are described. This was achieved by an electrophile-triggered ring expansion and 1,2-metallate rearrangement of vinylcyclopropyl boron-ate complexes generated from novel vinylcyclopropyl boronic esters. Electrophilic activation of the alkene double bond forms a carbocation beta- to the boron-ate moiety, triggering concomitant expansion of the cyclopropane ring to a cyclobutane and 1,2-metallate rearrangement from boron to give the cyclobutyl boronic ester product with a high degree of diasteroselectivity. Attempts to extend this methodology to the synthesis of dihydropyridine spirocycles are also briefly discussed. Finally, the synthesis of dihydropyridine spirocycles was achieved by an electrophile-induced dearomative semi-pinacol rearrangement of hydroxycyclobutylpyridines. This reaction was successfully applied to a variety of acylating agents and substituted hydroxycycloalkylpyridine species.

Polyketide natural products are of particular interest due to their highly specific and potent biological activity and structural diversity. The recurring motifs, such as (deoxy)propionate or acetate, often present in this class of molecules can be synthesised through iterative processes. Bahamaolide A and mycapolyol E contain an extended 1,3-polyol, comprising nine or ten stereodefined 1,3-related hydroxyl groups, respectively; to date, the total synthesis of these compounds has not been reported. Herein the application of an iterative protocol to construct the 1,3-polyol is described; specifically, asymmetric diboration of a terminal alkene followed by primary-selective homologation of the resulting 1,2-bis(boronic ester) with an enantiopure carbenoid bearing a pendent alkene primed to undergo subsequent diboration. When performed iteratively this enabled the synthesis of a 1,3-poly(boronic ester) with exquisite levels of stereocontrol. Functional group interconversions were not necessary between iterations, since the boronic esters themselves masked the hydroxyl functionality, which was revealed in a later stereospecific oxidation. This was employed in a bidirectional manner to prepare the 1,3-polyol in bahamaolide A. Diboration-homologation-diboration proved a step-efficient approach to rapidly access a C₂-symmetric octa(boronic ester) from 1,4-pentadiene. The octa(boronic ester) was desymmetrised through sequential homologation at the terminal primary boronic esters before poly(oxidation) where eight boronic esters were converted to the corresponding polyol in one operation. Cross-metathesis then a Horner-Wadsworth-Emmons reaction proceeded with high selectivity for six E-alkenes. The first total synthesis of bahamaolide A was completed in fourteen steps (LLS). The 1,3-polyol in mycapolyol E is not C₂-symmetric and so the iterative protocol was applied unidirectionally. The C5 stereocentre in mycapolyol E was assigned through synthesis of both diastereomers of the eastern fragment and comparison of NMR data with the isolated natural product. This work discusses the optimised synthesis of the three fragments, their combination through lithiation-borylation reactions and endgame model studies.

A new method has been developed to obtain densely functionalised cyclobutanes, wherein α-halo maleimides undergo sensitised [2+2] photocycloaddition under UV (366 nm) conditions to give α-halocyclobutanes and cyclobutenes in a highly regioselective manner in up to 78% yields over multiple steps. The dehalogenation of the α-chloride, by visible-light photocatalysis, gives a tertiary cyclobutyl radical, leading to radical addition to a range of suitable substrates to form a quaternary carbon-carbon bond in a diastereoselective manner in up to 94% yields of the desired highly functionalised cyclobutane. The protocol shows broad functional group tolerance and the succinimide ring can be further functionalised regioselectively in a variety of ways. These results are discussed in Chapter 1. A novel approach towards cyclobutyl spirocycles was developed. An alkyne tethered redox active ester was found to undergo a visible-light [2+2] photocycloaddition with a maleimide to give a cyclobutene containing a redox active tether using a novel thioxanthone sensitiser. Introducing a diboron source such as B₂cat₂, acts as a reductant and produces alkyl radical. The pertinent radical undergoes 5-exotrig cyclisation forming a cyclobutyl spirocycle which can trap out boron to give the desired functionalised cyclobutane. The development of this methodology is discussed in Chapter 2. A total synthesis of albiflorin has been undertaken. The current proposed route was based on the protocol developed described in Chapter 1, and therefore has scalability and is transition-metal free. The synthetic route and methodology developed is discussed in Chapter 3.

Cystic fibrosis (CF), one of the most common genetic conditions in the UK, is caused by a mutation of the cystic fibrosis transmembrane regulator (CFTR) gene. CF related liver disease (CFLD) affects up to 30% of the CF population and is the 3rd most common cause of death in CF. Liver fibrosis is generated in response to ongoing chronic liver injury and results in the deposition of a pathologic collagen-rich extracellular matrix (ECM). Typically, CFLD initially develops as a focal biliary fibrosis, but can progress to a multilobular cirrhosis, with disrupted hepatic cell function, portal hypertension and ultimately liver failure. For end stage CFLD a liver transplant is the only curative option available. CFTR expression has previously been identified in cholangiocytes. CFLD is thought to originate from dysfunctional cholangiocytes with altered CFTR expression, but how this promotes fibrotic ECM deposition is not understood. In other instances of liver disease, hepatic stellate cells (HSCs) are key effector cells for fibrotic matrix deposition. After liver injury, HSCs activate into proliferative myofibroblasts and migrate through the liver depositing ECM components such as type-I collagen. In CFLD, the role of HSCs and the effect of CFTR mutation on HSC function in the production of liver fibrosis is unknown. The work presented in this thesis demonstrates for the first time that HSCs have an independent role in the production of liver fibrosis in CFLD. Quiescent HSCs with knockout of CFTR demonstrate pro-fibrotic characteristics and produce pro-fibrotic markers. Activated HSCs with knockout of CFTR have increased proliferation and fibrogenesis but reduced motility, potentially accounting for the focal nature of CFLD. In vivo, a global ΔF508 mutation of CFTR caused the most severe liver fibrosis, suggesting defects in other cells, such as cholangiocytes, perpetuates the fibrotic response. Single-nuclei RNA sequencing indicated several potential mechanistic pathways for the amplified fibrotic response in CFLD. Clinically, there is no reliable test to identify patients with CF that have developed CFLD. In this thesis we propose New Diagnostic Criteria incorporating FibroScan as a reliable diagnostic tool. Nevertheless, FibroScan has limitations, particularly given the focal nature of CFLD. Therefore, newer imaging modalities are required and contrast enhanced magnetic resonance imaging to calculate the extra cellular volume of the liver appears promising. CFLD poses an important cause of both morbidity and death in a young patient population. The results presented here demonstrate that the 'New Diagnostic Criteria' significantly improve CFLD detection. For the first time CFTR-null HSCs have been shown to have pro-fibrotic characteristics and potential pathways leading to HSC activation in CFLD have been identified. Improved clinical detection and better understanding of mechanistic pathways that promote liver fibrosis in CF may help identify potential therapeutic targets for CFLD.

Part I: Synthesis of a Stable, Fluorinated Thromboxane A2 Analogue and its Application as a Hapten for Monoclonal Antibody Generation. Cardiovascular disease (CVD) is the leading cause of death worldwide, accounting for more deaths per annum than cancer, diabetes, and respiratory diseases combined. One contributing factor to CVD is the overexpression of thromboxane A2 (TxA2)-a member of the prostanoid family of natural products that assists with blood clot formation. Pharmacological inhibition of TxA2 has so far failed to meet expectations due to issues related to selectivity, toxicity, or efficacy. To overcome these problems, a TxA2-specific monoclonal antibody has been proposed; however, the short half-life of TxA2 (t½ = 32 s, pH 7.4) renders this impossible. In this respect, 10-fluorothromboxane A2 (F-TxA2) has been developed as a stable TxA2 mimic using a 15 step process from a key building block that the Aggarwal group has used routinely in the synthesis of several prostaglandins. Unfortunately, this route to F-TxA2, and other thromboxanes of interest, is particularly long and involves significant synthetic challenges. Alongside this, F-TxA2 itself is not immunogenic and must be attached to a large carrier protein such as keyhole limpet hemocyanin (KLH) in a structural design known as an antigen, which is required to elicit an immune response. This thesis details the development of both an improved strategy towards the total synthesis of thromboxanes, with a focus on thromboxane B2 (TxB2) a natural metabolite of TxA2, as well as the synthesis of a tetra-valent F-TxA2-containing antigen. In the former, a key oxidative ring-expansion provided rapid access to the core of the thromboxanes in the form of a hemi-acylal intermediate. However, the sensitive nature of this species and its downstream intermediates towards epimerisation ultimately required various route re-designs. This was able to be overcome with a diastereoselective dynamic kinetic resolution process to provide stereocontrolled access to a unique acylal that is currently being evaluated for its potential in the improved total synthesis of TxB2 and eventually F-TxA2. In the latter work, F-TxA2 isolated from the initial total synthesis was rendered immunogenic by coupling to a tri-lysine peptide and conjugating to KLH. This strategy allowed for the preparation of a tetra-valent F-TxA2-containing antigen that has since been administered to murine hosts for the potential generation of TxA2-specific monoclonal antibody that could find use as a novel therapeutic for the treatment of CVD. Part II: Difunctionalisation of C-C -Bonds Enabled by Strained Boronate Complexes. Cyclobutanes are becoming increasingly prevalent within drug discovery programmes; however, access to this type of scaffold is generally limited by the lack of synthetic methods that permit its construction. In this respect, the synthesis of cyclobutanes, particularly those of defined geometry, is often the limiting step in medicinal chemistry. This section discloses the development of a modular approach to the diastereoselective synthesis of 1,1,3-trisubstituted borylcyclobutanes using bicyclobutyl boronate complexes. These strained intermediates were prepared through the reaction of bicyclobutyl lithium with boronic esters and found to be highly reactive with a broad range of electrophiles, facilitating the introduction of both a migrating group and an electrophile across the central C-C -bond in a formal difunctionalisation process. The unique reactivity of these highly strained boronate complexes was studied using in situ IR spectroscopy and showcased in a reaction with benzaldehyde, which was found to be complete after only 5 min at −78 °C. Furthermore, unique electrophiles such as carbon dioxide, which has not previously been shown to react with other boronate complexes, was amenable to the process. Density functional theory (DFT) calculations were also undertaken to provide a model for the stereochemical outcome of the process, and finally, the boronic ester handle was further derivatised into a range of useful functional groups to provide a third point of diversification. This methodology may find use within drug discovery programmes to rapidly build-up functionalised cyclobutanes for use in screening libraries.

The work described in this thesis is divided into two chapters; of which the first chapter explores the asymmetric synthesis of tertiary thiols by lithiation-electrophilic trapping of secondary dialkyl thiobenzoates and the second chapter investigates the lithiation-borylation chemistry of cyclobutyl benzoates.

Transient electronic and vibrational absorption spectroscopy (TEAS and TVAS, respectively) has been applied to the study of solution phase reactive mixtures relevant to synthetic methodology used in polymerisation and small molecule synthesis. The photochemical dynamics of three classes of organic photoredox catalysts (OPCs) employed in organocatalysed atom transfer radical polymerisation (O-ATRP) are studied. In total nine catalysts were selected for study with structures that vary around the N-aryl and core- substitution of dihydrophenazine, phenoxazine and phenothiazine scaffolds, each with varying propensities for control of polymerization outcomes. Experiments for both lifetime and photoinduced electron transfer measurements were recorded in three solvents of differing polarity: N'N-dimethylformamide (DMF), dichloromethane (DCM), and toluene. S1-state lifetimes are reported and range from 130 ps to 40 ns with considerable dependence on the photocatalyst structure and the solvent. Competition between ground-electronic state recovery and intersystem crossing controls triplet state populations and is a minor pathway in the dihydrophenazine derivatives but is of greater importance for phenoxazine and phenothiazine catalysts. Comparison of these results with previously reported O-ATRP performances of the various photoredox catalysts shows that high triplet-state quantum yields are not a pre-requisite for controlling polymer dispersity. The results call for a re-evaluation of the excited state properties of most significance in governing the photocatalytic behaviour of organic photoredox catalysts in O-ATRP reactions. Spectroscopic signatures of the OPC excited states, electron acceptors and products of photoinduced electron transfer are tracked over sub-picosecond to nanosecond and microsecond time-intervals. Trends in bimolecular electron transfer rate coefficients are rationalized using a modified Marcus-Savéant theory of dissociative electron transfer and show that the Gibbs energy change is the major determinant of electron transfer rates in OPCs relevant for ATRP. TVAS is applied to a recently reported reaction involving the addition of an electron-deficient alkyl radical to the strained σ‐bond of a bicyclo[1.1.0]butyl boronate complex to form a cyclobutyl boronic ester. The previously proposed single electron transfer mechanism does not adequately account for the observed spectral and kinetic data. Instead, iodine atom transfer is shown to be the preferred pathway for this reaction and is likely to be operative for other reactions of this type.

The homologation of boronic esters using lithiated Hoppe-type diisopropylcarbamates and Beak-type 2,4,6-triisopropylbenzoate (TIB) esters represents an efficient process for the formation of carbon-carbon bonds in a highly stereoselective manner. This process is referred to as lithiation-borylation. Studying this reaction using in situ IR spectroscopy has revealed reaction times for a series of alkyl carbamates and TIB esters. Alkyl TIB esters undergo lithiation faster than their corresponding carbamates, and the lithiated alkyl carbamates undergo faster borylations than the lithiated TIB esters. It is discussed how the size and coordinating ability of each directing group could lead to these differences. Varying solvent has also provided evidence on the factors that affect lithiation and borylation. Using in situ IR spectroscopy, the lithiation-borylation of alkyl TIB esters has been further optimised, where lithiations are now performed in toluene and borylations with the addition of THF. Boranes, boronic esters and borate esters all react with lithiated TIB esters at a similar rate providing further evidence for a pre-complexation event between the lithium carbenoid and the Lewis basic oxygen atoms. The use of a proximal aromatic group leads to rapid borylations of diamine-ligated lithiated carbenoids, providing further evidence for a cation- interaction between the aromatic group and lithium atom of the carbenoid. By generating the lithiated species under diamine-free conditions, the effects of various additives have been explored. In situ IR spectroscopy was then employed to study the lithiation-borylation of a set of O-cycloalkyl TIB esters (cyclopropyl through to cyclohexyl). Only the cyclobutyl TIB ester underwent the full process in practical yields. It is described as occupying a "Goldilock's zone" where the ring is small enough to allow facile deprotonation without decomposition, but large enough to allow 1,2-migration to occur. The lithiation-borylation reaction has been optimised on a Chemspeed batch automation platform using a model boronic ester. We have shown homologations with either LiCH2Cl (the Matteson reaction) or a lithiated benzoate (derived from the -stannyl benzoate) proceed in ~90% yield per step over 2 steps. Set up time for 4 reactions can be as little as 30 minutes with 1 iteration performed per day. A new automated synthesis of (+)-kalkitoxin analogues was designed. The starting point for the synthesis (a thiazoline bearing boronic ester) was synthesised in the lab in 6 steps starting from protected L-cysteine. The final steps of the total synthesis are Morken amination of a boronic ester, amidation and then methylation of the amide. We have shown the 3-step sequence works well on the automated platform for phenethyl boronic acid pinacol ester (42% over 3 steps) however for a model thiazoline bearing boronic ester the thiazoline undergoes rapid (1 h) isomerization to the thiazole (isolated in 46% over 3 steps) under the basic conditions required for the amination.

Modern approaches to organic synthesis often look to break down target molecules into key molecular fragments. These fragments, or "building blocks", require reactive functional groups that enable the target molecule to be assembled efficiently and selectively through the formation of new C-C or C-heteroatom bonds. This thesis outlines investigations into novel coupling reactions, which harness the inherent strain energy of small-ring cyclic building blocks. The key reaction mechanisms explored are strain-release-driven 1,2-rearrangement reactions. Firstly, investigations into the 1,2-metallate rearrangement of boronate complexes with an activated cyclopropane α to boron are described. In addition, the strain-release of azabicyclo[1.1.0]butane was explored as the driving force for the 1,2-metallate rearrangement reaction. Finally, investigations into a novel strain-release semipinacol rearrangement reaction were undertaken. All three reaction mechanisms facilitated the formation of a new C-C bond and provide access to novel molecules with interesting sp3-rich scaffolds and diverse functionality.

This thesis details the development of novel decarboxylative radical addition reactions to vinyl boronic esters using photoredox catalysis, enabling the efficient and rapid access of functionalised alkyl boronic esters from abundant feedstock chemicals. Key to the success of these methodologies is the stabilised α-boryl radical intermediate generated upon radical addition to the vinyl boronic ester, which can undergo a range of terminating events to yield a diverse library of complex boronic ester products. Firstly, the decarboxylative radical addition reaction of carboxylic acids to vinyl boronic esters was developed to directly access alkyl boronic esters using photoredox catalysis. The reaction was applied to a range of carboxylic acids, including α-amino, α-oxy and alkyl acids providing the corresponding boronic ester products in good to excellent yields. Moreover, the reaction could be applied to a range of substituted vinyl boronic esters. Mechanistic studies confirmed a radical-polar crossover mechanism, involving an unprecedented single-electron reduction of the α-boryl radical to the corresponding α-boryl anion, which is subsequently protonated. Having set the stage for photoredox-mediated decarboxylative radical additions to vinyl boronic esters, we demonstrated that we could trap the α-boryl anion with an electrophile tethered to the vinyl boronic ester, enabling the synthesis of highly functionalised, polysubstituted cyclopropyl boronic esters. Mechanistic studies supported a radical-polar crossover mechanism involving an intramolecular SN2 cyclisation to yield the cyclopropane. Finally, to introduce further molecular complexity into these molecules, a decarboxylative conjunctive cross-coupling of vinyl boronic esters with carboxylic acids and aryl iodides using metallaphotoredox catalysis was developed. Trapping of the intermediate α-boryl radical with an aryl nickel complex enabled a cross-coupling event to yield complex benzylic boronic ester products. A range of α-amino acids, mainly secondary amino acids, and tertiary α-oxy acids with aryl iodides were successfully employed and the methodology was applied to the synthesis of four sedum alkaloid natural products.

In the search for high affinity therapeutics, medicinal chemists are turning their attention to free ligand conformations as it is well known that if a large conformational reorganisation is required upon binding, then a weaker binding affinity will be observed. This has been highlighted as an important strategy in the inhibition of protein–protein interactions (PPIs), due to the large, flat and featureless binding sites they present. This thesis discusses the design, synthesis and conformational analysis of a novel class of conformationally controlled α-helix mimetics, aimed at targeting aberrant PPIs. Their ability to target the p53-Mdm2 PPI with reasonable affinity is demonstrated. Molecular Mechanics (MM) conformational search calculations were used to design a conformationally controlled scaffold that mimicked the i, i + 3/4 and i + 7 positions of the α-helix. Following the design of a general scaffold, appropriate side chains were added to mimic those of p53, and protein-ligand molecular docking calculations were performed to assess the binding of the designed ligand to Mdm2. Molecular docking was also used to design a library of p53 mimetics with binding affinities comparable to that of Nutlin-2, a highly successful p53-Mdm2 inhibitor. With promising p53 mimetics designed using computation, their synthesis was explored using lithiation–borylation. Using lithiation–borylation a diverse set of side chains can be incorporated onto the scaffold by the insertion of the correct benzoate ester into the synthetic sequence. Thus, broad libraries of α-helix mimetics bearing different side chains can be synthesised using the same iterative methodology. To confirm that the designed p53 mimetics exhibit the conformational bias that was predicted by MM calculations, a hybrid quantum mechanics (QM) and NMR spectroscopy approach was used to explore the conformation of one of the p53 mimetics. Experimentally measured scalar coupling constants, interproton distances derived from 1D-NOESY spectroscopy and both 1H and 13C chemical shifts were compared to the Boltzmann averaged values, calculated using DFT calculations. An excellent correlation was observed between the two data sets, confirming the predicted conformational bias. Finally, the binding of the p53 mimetics to Mdm2 was explored using 1H15N HSQC spectroscopy. The chemical shift perturbations (CSPs) that were observed upon binding of the ligands were mapped to amino acids located primarily in, or on the periphery of, the p53 binding pocket on Mdm2. The CSPs were tracked with increasing concentrations of ligand to obtain dissociation constants (Kd). Two different p53 mimetics were tested and binding affinities as low as 8.8 μM were obtained. Additionally, the binding of two control molecules was assessed using 1H15N HSQC spectroscopy, to confirm the importance of both the hot-spot groups and conformational control in obtaining high affinity therapeutics.

The asymmetric synthesis of organic molecules is of fundamental importance to the design and preparation of new drug and agrochemical compounds. The treatment of a boronic ester with a metal carbenoid, termed a homologation reaction, is a useful strategy for accessing stereodefined boronic esters, which can participate in a plethora of transformations. This thesis reports the development of three new methods for the homologation of boronic esters and details their application towards the synthesis of complex molecules. Firstly, enantio- and diastereopure α-sulfinyl benzoate building blocks were explored as carbenoid precursors for the homologation of boronic esters. A range of functionalised αsulfinyl benzoates were prepared in enantioenriched form by using either a lithiation‒ transmetallation‒trapping approach or through alkylation chemistry. These building blocks were transformed into stereodefined Mg and Li carbenoids, through sulfoxide‒metal exchange, and were found to homologate boronic esters in a highly stereospecific fashion. This homologation process was rendered iterative, which allowed a molecule bearing three contiguous stereocentres to be accessed as a single stereoisomer. Secondly, lithiated terminal epoxides were explored as reagents for the preparation of βoxyboronic esters. Our goal was to use this transformation, in conjunction with a preestablished homologation protocol, to access polypropionate motifs, which are frequently encountered in the polyketide family of natural products. However, due to a poor reactivity profile and issues regarding the stability of β-oxyboronic esters, this strategy was abandoned. Finally, lithiated epoxysilanes were used to achieve the vinylidene homologation of boronic esters. This reaction allowed access to a diverse range of sp3-rich vinyl boronic esters, many of which would be difficult to prepare by other means. A divergence in mechanism was observed for some sp2-hybridised starting boronic esters, which were found to deliver the corresponding vinyl silane products. This mechanistic divergence was probed using computation, which revealed that the reaction outcome could be rationalised by considering the stabilisation of negative charge in the transition-state of the elimination step. The vinylidene homologation reaction was applied to achieve a short and stereoselective synthesis of the proposed structure of machillene, however the NMR data of our synthetic sample did not match that which was reported. Our efforts towards the structural revision of machillene are discussed.

The thesis describes the applications of lithiation-borylation methodology in polypropionate synthesis and the synthesis of organofluorine compounds. Firstly, an efficient method for the synthesis of polypropionate fragments based on building block assembly strategy using lithiation-borylation reaction has been developed. Benzoate ester 302 can react with boronic ester 347 efficiently via lithiationborylation reaction and subsequent oxidation to afford alcohol 353 in good yield and with excellent diastereoselectivity, which can be applied in the synthesis of polypropionate fragment 358, a key intermediate of 6-deoxyerythronolide. Some limitations, such as substrate control and O-migration, were observed in the reaction process. Secondly, we extensively explored the introduction of difluoromethyl and monofluoromethyl groups by lithiation-borylation reaction with organoboronic esters. The difluoromethylation and monofluoromethylation reactions proved to be very challenging due to the instability of in situ generated fluorinated carbanion 417 or 423. Generally, the formation of boronate complex 419 or 424 was not detected. Additionally, we proposed some other strategies for the future work.

This thesis documents the contributions made to four projects under the broad theme of boron homologation reactions of 1,2-bis(boronic esters). This work culminated in efforts towards the total synthesis of Bahamaolide A, a newly isolated oxopolyene macrolide.

This thesis is composed of two chapters reporting contributions to two different projects. The first chapter presents a research project aiming to develop a new class of helical molecules which, upon activation from an external stimulus, would be able to reversibly switch from one screw-sense to the other. All-syn methyl-substituted hydrocarbons, as described by Aggarwal in 2014, were shown to adopt helical conformations with very high levels of control. More importantly, one of these unique molecules could access either the M or the P screw-sense, depending on its physical state. Therefore, all-syn methyl-substituted hydrocarbons seemed to be promising candidates for the design of a new class of molecular switches. A diamond lattice-based analysis revealed that the number of syn-pentane and gauche interactions in the chain was one of the key parameters that dictated its conformational preference. A series of six compounds of different chain lengths was designed and synthesised using an efficient bidirectional iterative homologation of C2-symmetric boronic esters. A QM/NMR approach was employed to quantitatively describe the conformational landscape of these molecules and confirmed the diamond lattice-based model with a good degree of confidence. A screening of different substituents at the termini revealed that alkyne, hydroxyl, amino or aromatic groups could be considered as 'small' groups, favouring the helical conformer with both terminal dihedral angles in a gauche conformation. However, the combined effects of two tert-butyl groups might force both terminal dihedral angles to adopt an antiperiplanar conformation, thus favouring the opposite screw-sense. These findings set the experimental basis to design a new molecular switch. The first part of the second chapter describes the development of a new decarboxylative borylation methodology and its application to the synthesis of a-amino boronic esters. Some medicinal chemistry-type examples and three additional natural products have been added to the substrate scope. Key mechanistic experiments were conducted to prove the radical pathway and provide support for an outer sphere radical trapping process. In the second part, a study on the decarboxylative borylation of amino acids was conducted. First, the reaction conditions were optimised on a proline derivative. With these new conditions in hand, other activated amino acids were tested. However, most of them did not afford the desired products. To identify the cause of failure, a number of parameters were investigated (the effects of free N-H bonds, redox potentials and protecting groups). A different mode of activation involving the use of hypervalent iodine derivatives was attempted but failed to provide the desired products. Finally, a limited substrate scope composed of proline derivatives was subjected to the reaction conditions. Unfortunately, none of these examples gave the desired product.

This thesis reports the application of computational modelling, NMR spectroscopy and stereospecific iterative homologation of boronic esters to the three-dimensional structural elucidation of flexible organic small molecules, and the design and synthesis of flexible molecules with tailored conformations. Firstly, the configuration of a recently isolated polyketide baulamycin A, which exhibits potent antibacterial activity, was reassigned using a combination of Density Functional theory (DFT) calculations, NMR spectroscopy and synthesis. In this work, DFT calculations were employed to predict the complex dynamic conformations of eight possible diastereomers of baulamycins and to compute the ensemble-averaged chemical shifts, 1H-1H scalar coupling constants and 1H-1H distances. Comparison between the computed NMR parameters of each diastereomer with the experimentally determined values eliminated 112 out of the possible 128 diastereomeric candidates. Finally, synthesis allowed the relative and absolute configuration of baulamycin A to be positively identified. Secondly, inspired by the conformational control exerted by quaternary centres, a range of conformationally defined unnatural amino esters were designed with the aid of computational modelling. Two of the amino esters were synthesised and their solution state conformations were elucidated by a combination of DFT calculations and quantitative analysis of 1H-1H and 1H-13C scalar coupling constants. Their side chains are shown to take on defined orientations (syn-periplanar or turn a 120° corner) with controllable distances and could find application in areas such as drug design. Finally, factors controlling the helical screw-sense of hydrocarbons with all-syn contiguous methyl substituents was investigated. The solution-state conformational behaviour of hydrocarbons with different numbers of methyl substituents (from six to 11) was studied using a combination of DFT calculations and quantitative analysis of 1H-1H scalar coupling constants and 1H-1H distances. It was discovered that only hydrocarbons with even numbers of methyl substituents adopt regular helical conformation, whereas hydrocarbons with odd number of methyl substituents do not have a strong preference for a particular conformation. The preference of screw sense (if any) in each case was rationalised by the minimisation of gauche interactions.

The work described in this thesis details the development of new classes of metallated carbenoids to be used in the homologation of boronic esters. 2-Phenyl-azetidinium ylide, generated in situ by deprotonation of 2-phenylazetidinium triflate, reacted with boronic esters to give, after ring-opening 1,2-metallate rearrangement, γ-dimethylamino tertiary boronic esters. The process proved to be not stereospecific, owing to the configurational instability of the generated intermediated ylide, which presumably exists in equilibrium with the open chain carbene species. The use of enantioenriched α-sulfinyl benzoates as precursors to lithium and magnesium carbenoids for the stereoselective reagent-controlled homologation of boronic esters has also been developed. α-Sulfinyl benzoates could be synthesised in very high enantiopurity from racemic lithiated benzoates by transmetalation to the corresponding magnesiated benzoates followed by electrophilic trapping with enantiomerically pure Andersen’s sulfinate. Alternatively, the α-sulfinyl benzoates could be prepared by alkylation of methylene α-sulfinyl benzoate. The carbenoid precursors were subsequently employed in the homologation of boronic esters, a process that proved to be efficient using either t-BuLi or i-PrMgClžLiCl to trigger the sulfoxide−metal exchange, giving the homologated products in high yield and excellent stereofidelity. The development of one-, two- and three-carbon building blocks for the homologation of boronic esters enabling the introduction of diverse functional groups has also been investigated.

This thesis reports contributions to three branches of organoboron chemistry: boron incorporation, boron homologation, and boron functionalization. Firstly, a decarboxylative borylation reaction has been developed. Carboxylic acids, pre-activated as their corresponding N-hydroxyphthalimide esters, have been found to undergo a decarboxylative borylation process in the presence of bis(catecholato)diboron in N,N-dimethylacetamide solvent under blue LED irradiation to deliver, after transesterification with pinacol, stable and isolable pinacol boronic esters. These simple conditions extended to a wide range of functional group-bearing and structurally diverse carboxylic acids to give the corresponding boronic esters in mostly good to excellent yields. Mechanistic studies have revealed that a single electron transfer between the activated ester and bis(catecholato)diboron, which form a light-absorbing EDA complex, is responsible for initiating the transformation, and that the ability of the solvent to stabilize boryl radicals is critical to successful reaction. Secondly, the Aggarwal lithiation−borylation methodology has been expanded to enable the synthesis of 1,3-diols, which were previously inaccessible due to beta-elimination of the intermediate boronate complexes. 1,2-Bis(boronic esters) were discovered to undergo stereo- and regioselective homologation using enantioenriched lithium carbenoids in the presence of bulky diamines, such as sparteine. The resultant 1,3-bis(boronic esters) were oxidized to deliver a wide range of structurally diverse secondary-secondary and secondary-tertiary 1,3-diols in good to excellent yields and perfect diastereoisomeric ratios, the latter of which is especially noteworthy since these substrates have not previously been accessible with such generality and high diastereoselectivity. Finally, we have developed a novel, strained bicyclobutyl boronate complex that has enabled, for the first time, the reaction of C−C sigma-bonds of boronate complexes with electrophiles. We have invented a linchpin reagent, a bicyclobutyl sulfoxide, that enables the facile generation of bicyclobutyl lithium on demand, which then reacts with a boronic ester to form the bicyclobutyl boronate complex. These highly reactive intermediates have been reacted with electrophiles to produce a set of pharmaceutically-relevant 1,1,3-trisubstituted borylated cyclobutanes with excellent diastereoselectivity. Of note, electrophilic palladium(II)-aryl complexes were found to be excellent electrophiles and have enabled the addition of two modular units, a boronic ester and an aryl triflate, across a C−C sigma-bond. This reaction constitutes the first report of a C−C sigma-bond carbopalladation, albeit a highly strained one.

A three carbon homologation of pinacol boronic esters has been developed. The procedure consists of a one pot Matteson homologation/alkylation followed by a palladium catalysed rearrangement from the branched to the linear allylic boronic ester. The procedure allows for the synthesis of a broad range of disubstituted and trisubstituted allylic boronic esters with high E selectivity. Combining this methodology with lithiation-borylation allows for the synthesis of carbon chains bearing 1,5-stereogenic centres and its utility has been demonstrated in a formal synthesis of (+ )-jasplakinolide. The palladium catalysed reactivity of allylic boronic esters has been further explored by coupling with a range of different nucleophiles. Allylic boronic esters have been successfully coupled with carbon, oxygen and nitrogen based nucleophiles giving products with high E selectivity and high linear to branched ratios. Work has also been carried out towards developing a carbenoid which can be used for a reagent controlled homologation of a boronic ester introducing oxygen functionality. Various carbenoids have been prepared however none could be successfully applied to a reagent controlled homologation reaction