Radical approaches to alangium and mitragyna alkaloids

Abstract The work presented in this thesis has focused on the development of novel and concise syntheses of Alangium and Mitragyna alkaloids, and especial approaches towards (±)-protoemetinol (a), which is a key precursor of a range of Alangium alkaloids such as psychotrine (b) and deoxytubulosine (c). The approaches include the use of a key radical cyclisation to form the tri-cyclic core. Chapter 1 gives a general overview of radical chemistry and it focuses on the application of radical intermolecular and intramolecular reactions in synthesis. Consideration is given to the mediator of radical reactions from the classic organotin reagents, to more recently developed alternative hydrides. An overview of previous synthetic approaches to a range of Alangium and Mitragyna alkaloids is then explored. Chapter 2 follows on from previous work within our group, involving the use of phosphorus hydride radical addition reactions, to alkenes or dienes, followed by a subsequent Horner-Wadsworth-Emmons reaction. It was expected that the tri-cyclic core of the Alangium alkaloids could be prepared by cyclisation of a 1,7-diene, using a phosphorus hydride to afford the phosphonate or phosphonothioate, however this approach was unsuccessful and it highlighted some limitations of the methodology. Chapter 3 explores the radical and ionic chemistry of a range of silanes. Initial studies explored the radical addition of a range of silicon hydrides to alkenes to afford the corresponding hydrosilylation products. The chemistry of the hydrosilylation products was then explored – it was hoped that a subsequent Peterson olefination or Fleming-Tamao oxidation would afford the corresponding alkene or alcohol. Subsequent investigations looked into the possibility of combining the radical and ionic reactions, to afford alkenes or alcohols, in a one-pot transformation. Chapter 4 explores the radical cyclisation of various compounds, including unsaturated alpha-haloamides (d and e), xanthates (f), vinyl bromides (g and h). For this, a robust and efficient synthesis of an allyl tetrahydroisoquinoline core (i and j) was developed, following conversion into the desired radical precursors these compounds were treated with tributyltin hydride and a radical initiator. Finally, Chapter 4 investigates the radical cyclisation of some unsaturated phenylselenides (k and l), which resulted in the isolation of the desired target alkaloid (±)-protoemetinol (a) in 4 steps and in 2% overall yield. Chapter 5, which builds on previous work within Chapter 4, discusses the cyclisation of vinyl bromides bearing an a,β-unsaturated ester (n and o). This resulted in short 4-step syntheses of both (±)-des-methyl-protoemetinol (m) and (±)-protoemetinol (a) (along with some epimers). Subsequent studies then expanded the synthetic strategy to include the synthesis of a structurally simpler analogue of mitragynine (p).EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Mechanisms of Acute Eosinophil Mobilization from the Bone Marrow Stimulated by Interleukin 5: The Role of Specific Adhesion Molecules and Phosphatidylinositol 3-Kinase

Mobilization of bone marrow eosinophils is a critical early step in their trafficking to the lung during allergic inflammatory reactions. We have shown previously that the cytokine interleukin (IL)-5, generated during an allergic inflammatory reaction in the guinea pig, acts systemically to mobilize eosinophils from the bone marrow. Here, we have investigated the mechanisms underlying this release process. Examination by light and electron microscopy revealed the rapid migration of eosinophils from the hematopoietic compartment and across the bone marrow sinus endothelium in response to IL-5. Using an in situ perfusion system of the guinea pig hind limb, we showed that IL-5 stimulated a dose-dependent selective release of eosinophils from the bone marrow. Eosinophils released from the bone marrow in response to IL-5 expressed increased levels of β2 integrin and a decrease in L-selectin, but no change in α4 integrin levels. A β2 integrin–blocking antibody markedly inhibited the mobilization of eosinophils from the bone marrow stimulated by IL-5. In contrast, an α4 integrin blocking antibody increased the rate of eosinophil mobilization induced by IL-5. In vitro we demonstrated that IL-5 stimulates the selective chemokinesis of bone marrow eosinophils, a process markedly inhibited by two structurally distinct inhibitors of phosphatidylinositol 3-kinase, wortmannin and LY294002. Wortmannin was also shown to block eosinophil release induced by IL-5 in the perfused bone marrow system. The parallel observations on the bone marrow eosinophil release process and responses in isolated eosinophils in vitro suggest that eosinophil chemokinesis is the driving force for release in vivo and that this release process is regulated by α4 and β2 integrins acting in opposite directions

Chronic testicular Chlamydia muridarum infection impairs mouse fertility and offspring development

With approximately 131 million new genital tract infections occurring each year, Chlamydia is the most common sexually transmitted bacterial pathogen worldwide. Male and female infections occur at similar rates and both cause serious pathological sequelae. Despite this, the impact of chlamydial infection on male fertility has long been debated, and the effects of paternal chlamydial infection on offspring development are unknown. Using a male mouse chronic infection model, we show that chlamydial infection persists in the testes, adversely affecting the testicular environment. Infection increased leukocyte infiltration, disrupted the blood:testis barrier and reduced spermiogenic cell numbers and seminiferous tubule volume. Sperm from infected mice had decreased motility, increased abnormal morphology, decreased zona-binding capacity, and increased DNA damage. Serum anti-sperm antibodies were also increased. When both acutely and chronically infected male mice were bred with healthy female mice, 16.7% of pups displayed developmental abnormalities. Female offspring of chronically infected sires had smaller reproductive tracts than offspring of noninfected sires. The male pups of infected sires displayed delayed testicular development, with abnormalities in sperm vitality, motility, and sperm-oocyte binding evident at sexual maturity. These data suggest that chronic testicular Chlamydia infection can contribute to male infertility, which may have an intergenerational impact on sperm quality

Fission Yeast Cells Undergo Nuclear Division in the Absence of Spindle Microtubules

Through a previously undescribed mechanism, fission yeast cells can undergo nuclear division and enter the next cell cycle, even in the absence of spindle microtubules

Kinetics of Eotaxin Generation and Its Relationship to Eosinophil Accumulation in Allergic Airways Disease: Analysis in a Guinea Pig Model In Vivo

Challenge of the airways of sensitized guinea pigs with aerosolized ovalbumin resulted in an early phase of microvascular protein leakage and a delayed phase of eosinophil accumulation in the airway lumen, as measured using bronchoalveolar lavage (BAL). Immunoreactive eotaxin levels rose in airway tissue and BAL fluid to a peak at 6 h falling to low levels by 12 h. Eosinophil numbers in the tissue correlated with eotaxin levels until 6 h but eosinophils persisted until the last measurement time point at 24 h. In contrast, few eosinophils appeared in BAL over the first 12 h, major trafficking through the airway epithelium occurring at 12–24 h when eotaxin levels were low. Constitutive eotaxin was present in BAL fluid. Both constitutive and allergen-induced eosinophil chemoattractant activity in BAL fluid was neutralized by an antibody to eotaxin. Allergen-induced eotaxin appeared to be mainly in airway epithelium and macrophages, as detected by immunostaining. Allergen challenge of the lung resulted in a rapid release of bone marrow eosinophils into the blood. An antibody to IL-5 suppressed bone marrow eosinophil release and lung eosinophilia, without affecting lung eotaxin levels. Thus, IL-5 and eotaxin appear to cooperate in mediating a rapid transfer of eosinophils from the bone marrow to the lung in response to allergen challenge

Targeting the Neurokinin Receptor 1 with Aprepitant: A Novel Antipruritic Strategy

Chronic pruritus is a global clinical problem with a high impact on the quality of life and lack of specific therapies. It is an excruciating and frequent symptom of e.g. uncurable renal, liver and skin diseases which often does not respond to conventional treatment with e.g. antihistamines. Therefore antipruritic therapies which target physiological mechanisms of pruritus need to be developed. Substance P (SP) is a major mediator of pruritus. As it binds to the neurokinin receptor 1 (NKR1), we evaluated if the application of a NKR1 antagonist would significantly decrease chronic pruritus.Twenty hitherto untreatable patients with chronic pruritus (12 female, 8 male; mean age, 66.7 years) were treated with the NKR1 antagonist aprepitant 80 mg for one week. 16 of 20 patients (80%) experienced a considerable reduction of itch intensity, as assessed by the visual analog scale (VAS, range 0 to 10). Considering all patients, the mean value of pruritus intensity was significantly reduced from 8.4 VAS points (SD +/-1.7) before treatment to 4.9 VAS points (SD +/-3.2) (p<0.001, CI 1.913-5.187). Patients with dermatological diseases (e.g. atopic diathesis, prurigo nodularis) had the best profit from the treatment. Side-effects were mild (nausea, vertigo, and drowsiness) and only occurred in three patients.The high response rate in patients with therapy refractory pruritus suggests that the NKR1 antagonist aprepitant may indeed exhibit antipruritic effects and may present a novel, effective treatment strategy based on pathophysiology of chronic pruritus. The results are promising enough to warrant confirming the efficacy of NKR1 antagonists in a randomized, controlled clinical trial

Mad3 KEN Boxes Mediate both Cdc20 and Mad3 Turnover, and Are Critical for the Spindle Checkpoint

Mitotic progression is controlled by proteolytic destruction of securin and cyclin. The mitotic E3 ubiquitin ligase, known as the anaphase promoting complex or cyclosome (APC/C), in partnership with its activators Cdc20p and Cdh1p, targets these proteins for degradation. In the presence of defective kinetochore-microtubule interactions, APC/C(Cdc20) is inhibited by the spindle checkpoint, thereby delaying anaphase onset and providing more time for spindle assembly. Cdc20p interacts directly with Mad2p, and its levels are subject to careful regulation, but the precise mode(s) of APC/C( Cdc20) inhibition remain unclear. The mitotic checkpoint complex (MCC, consisting of Mad3p, Mad2p, Bub3p and Cdc20p in budding yeast) is a potent APC/C inhibitor. Here we focus on Mad3p and how it acts, in concert with Mad2p, to efficiently inhibit Cdc20p. We identify and analyse the function of two motifs in Mad3p, KEN30 and KEN296, which are conserved from yeast Mad3p to human BubR1. These KEN amino acid sequences resemble ‘degron’ signals that confer interaction with APC/C activators and target proteins for degradation. We show that both Mad3p KEN boxes are necessary for spindle checkpoint function. Mutation of KEN30 abolished MCC formation and stabilised Cdc20p in mitosis. In addition, mutation of Mad3-KEN30, APC/C subunits, or Cdh1p, stabilised Mad3p in G1, indicating that the N-terminal KEN box could be a Mad3p degron. To determine the significance of Mad3p turnover, we analysed the consequences of MAD3 overexpression and found that four-fold overproduction of Mad3p led to chromosome bi-orientation defects and significant chromosome loss during recovery from anti-microtubule drug induced checkpoint arrest. In conclusion, Mad3p KEN30 mediates interactions that regulate the proteolytic turnover of Cdc20p and Mad3p, and the levels of both of these proteins are critical for spindle checkpoint signaling and high fidelity chromosome segregation

HIV/SIV Infection Primes Monocytes and Dendritic Cells for Apoptosis

Subversion or exacerbation of antigen-presenting cells (APC) death modulates host/pathogen equilibrium. We demonstrated during in vitro differentiation of monocyte-derived macrophages and monocyte-derived dendritic cells (DCs) that HIV sensitizes the cells to undergo apoptosis in response to TRAIL and FasL, respectively. In addition, we found that HIV-1 increased the levels of pro-apoptotic Bax and Bak molecules and decreased the levels of anti-apoptotic Mcl-1 and FLIP proteins. To assess the relevance of these observations in the context of an experimental model of HIV infection, we investigated the death of APC during pathogenic SIV-infection in rhesus macaques (RMs). We demonstrated increased apoptosis, during the acute phase, of both peripheral blood DCs and monocytes (CD14+) from SIV+RMs, associated with a dysregulation in the balance of pro- and anti-apoptotic molecules. Caspase-inhibitor and death receptors antagonists prevented apoptosis of APCs from SIV+RMs. Furthermore, increased levels of FasL in the sera of pathogenic SIV+RMs were detected, compared to non-pathogenic SIV infection of African green monkey. We suggest that inappropriate apoptosis of antigen-presenting cells may contribute to dysregulation of cellular immunity early in the process of HIV/SIV infection

Antibody Inhibition of a Viral Type 1 Interferon Decoy Receptor Cures a Viral Disease by Restoring Interferon Signaling in the Liver

Type 1 interferons (T1-IFNs) play a major role in antiviral defense, but when or how they protect during infections that spread through the lympho-hematogenous route is not known. Orthopoxviruses, including those that produce smallpox and mousepox, spread lympho-hematogenously. They also encode a decoy receptor for T1-IFN, the T1-IFN binding protein (T1-IFNbp), which is essential for virulence. We demonstrate that during mousepox, T1-IFNs protect the liver locally rather than systemically, and that the T1-IFNbp attaches to uninfected cells surrounding infected foci in the liver and the spleen to impair their ability to receive T1-IFN signaling, thus facilitating virus spread. Remarkably, this process can be reversed and mousepox cured late in infection by treating with antibodies that block the biological function of the T1-IFNbp. Thus, our findings provide insights on how T1-IFNs function and are evaded during a viral infection in vivo, and unveil a novel mechanism for antibody-mediated antiviral therapy

A quantitative systems view of the spindle assembly checkpoint

The idle assembly checkpoint acts to delay chromosome segregation until all duplicated sister chromatids are captured by the mitotic spindle. This pathway ensures that each daughter cell receives a complete copy of the genome. The high fidelity and robustness of this process have made it a subject of intense study in both the experimental and computational realms. A significant number of checkpoint proteins have been identified but how they orchestrate the communication between local spindle attachment and global cytoplasmic signalling to delay segregation is not yet understood. Here, we propose a systems view of the spindle assembly checkpoint to focus attention on the key regulators of the dynamics of this pathway. These regulators in turn have been the subject of detailed cellular measurements and computational modelling to connect molecular function to the dynamics of spindle assembly checkpoint signalling. A review of these efforts reveals the insights provided by such approaches and underscores the need for further interdisciplinary studies to reveal in full the quantitative underpinnings of this cellular control pathway