La découverte de l'Artémisinine, un 1,2,4-trioxacyclohexane, et le fait que la liaison endoperoxide est essentielle pour son activité antimalarique, a conduit les chimistes à la synthèse de nouvelles molécules contenant le motif endoperoxide pour obtenir de nouveaux leaders. Certains de ces composés peroxidiques sont les 1,2-dioxanes et les 1,2,4,5-tetraoxanes. À cet égard, la première partie de mon travail a été réalisée dans le laboratoire du professeur Giuseppe Campiani à l'université de Sienne et a inclus la synthèse d'analogues 1,2-dioxane du produit naturel Plakortine mais aussi le développement d'une stratégie de synthèse polyvalent du produit naturel 9,10-dihydroplakortine. Une des étapes clés dans notre approche synthétique a été la stéréosélectivité des réactions ainsi que la formation du squelette chiral 1,2-dioxane. En combinant l'époxidation dissymétrique de Sharpless à l'hydroperoxysilylation régiosélective d'alcène catalysée par le cobalt (II) de Mukaiyama-Isayama, la stéréochimie désirée a été obtenue. Dans la seconde partie de mon doctorat qui a pris place dans le laboratoire du professeur Paul O'Neill à l'université de Liverpool, la conception, la synthèse et l'évaluation du potentiel antimalarique de deux nouvelles séries de 1,2,4,5-tetraoxanes ont été réalisées. La première série de tetraoxanes, appelée les Mannoxanes, est une drogue hybride qui possède un noyau tetraoxane et une chaine latérale basique insérée grâce à une réaction de mannich. La seconde série a été préparée par une approche utilisant l'amination réductrice pour inclure la chaine latérale basique sur le noyau tetraoxane. Les deux séries ont montré d'excellentes activités antimalariques (de l'ordre du nanomolaire) contre plasmodium falciparum. / The discovery of artemisinin, a 1,2,4-trioxacyclohexane, and the fact that the endoperoxide bond is essential for its antimalarial activity has led chemists to synthesize new molecules containing the endoperoxide moiety in order to find new antimalarial hits. Some of these peroxidic compounds include the 1,2-dioxanes and the 1,2,4,5-tetraoxanes. In this regard, work on the first part of the PhD (Chapter 2) has been developed in the laboratories of Prof. Giuseppe Campiani at the University of Siena and includes the synthesis of 1,2-dioxane analogues of natural product Plakortin and the development of a versatile synthetic strategy to the natural compound 9,10-dihydroplakortin. One of the key issues in our synthetic approach has been the stereoselectivity of the reactions and the formation of the chiral 1,2-dioxane skeleton. By combining Sharpless asymmetric epoxidation to the Mukaiyama-Isayama Co(II)-catalyzed regioselective hydroperoxysilylation of an alkene, the desired stereochemistry has been obtained. In the second part of the PhD (Chapter 3), which has taken place in the laboratories of Prof. Paul O'Neill at the University of Liverpool, design, synthesis and assessment of the antimalarial potency of two new series of 1,2,4,5-tetraoxanes has been achieved. The first series of novel tetraoxanes are called Mannoxanes and are hybrid drugs that include a tetraoxane and a mannich basic phenol side-chain. The second new series has been synthesized by using a reductive amination approach to include the basic side chain in the tetraoxane molecule scaffold. Both of these series have shown excellent antimalarial activities against Plasmodium falciparum in the low nanomolar range.

In our continuing search for biologically active natural products from Madagascar as part of an International Cooperative Biodiversity Group (ICBG) program, a total of four antiproliferative extracts were studied, leading to the isolation of twelve novel compounds with antiproliferative activity against the A2780 human ovarian cancer line, and one extract with antimalarial activities was studied, which led to the isolation of five new natural products with antimalarial activities against the Dd2 and HB3 malarial parasites. The plants and their metabolites are discussed in the following order: one new xanthone and two known guttiferones from Symphonia tanalensis Jum. & H. Perrier (Clusiaceae); four new diphenyl propanes and one new cyclohepta-dibenzofuran skeleton from Bussea sakalava (Fabaceae); four new cardiac glycosides from Leptadenia madagascariensis Decne. (Apocynaceae); two new and four known alkaloids from Ambavia gerrardii (Baill.) Le Thomas (Annonaceae); five new sesquiterpene lactones from Polycline proteiformis Humbert (Asteraceae). The structures of all compounds were determined by analysis of their mass spectrometric, 1D and 2D NMR, UV and IR spectroscopic and optical rotation data. Other than structure elucidation, this dissertation also involve bioactivity evaluation of all the isolates, synthesis of two interesting alkaloids, as well as a proposal for the possible biosynthetic pathway of the new cyclohepta-dibenzofuran skeleton. / Ph. D.

As a part of a continuing search for bioactive compounds with the International Cooperative Biodiversity Group (ICBG), and in collaboration with the Natural Products Discovery Institute of the Institute for Hepatitis and Virus Research (IHVR), twelve plant extracts were investigated for their antiproliferative activity against the A2780 cell line, three plant extracts were investigated for their antimalarial activity against Plasmodium falciparum, and three plant extracts were investigated for their anti-inflammatory activity (PPAR-y inhibition). Bioassay-guided fractionation of extracts led to the identification of four new antiproliferative compounds (2.1-2.3, 3.1), five new anti-inflammatory compounds (6.4a, 6.5a-b, 6.6a, 6.6c), and twenty-eight known compounds from eight of the extracts. In addition, mallotojaponin C, an antimalarial natural product, and derivatives were synthesized and investigated for their antimalarial activity. / Ph. D.

As part of an International Cooperative Biodiversity Group (ICBG) program and a continuing search for antiproliferative natural products from the Madagascar rainforest, and a collaborative research project established between Virginia Tech and the Institute for Hepatitis and Virus Research (IHVR) focusing on searching for bioactive natural products from tropical forests in South Africa, 20 extracts were selected for investigation based on their antiproliferative activities against A2780 human ovarian cancer cell line or antimalarial activities against the Dd2 strain of Plasmodium falciparum. Bioassay-guided fractionation of seven of the extracts yielded twenty new compounds and twenty-four known compounds, and their structures were elucidated by using a combination of 1D (1H and 13C) and 2D NMR spectroscopy including COSY, HASQC, HMQC, HMBC, and NOESY sequences, mass spectrometry, UV, IR, ECD, optical rotation, and chemical conversions. In addition, ten known compounds were isolated from another five of the extracts, while studies on the remaining extracts were suspended due to loss of activity, unworkable small amounts of material, or low structural interest. The plants and their metabolites are discussed in the following order: five new antimalarial 5,6-dihydro-𝛼-pyrones and six bicyclic tetrahydro-𝛼-pyrone derivatives from Cryptocarya rigidifolia (Lauraceae); two new and five known antiproliferative lignans from Cleistanthus boivinianus (Phyllanthaceae); two new and two known antiproliferative sesquiterpenes lactones from Piptocoma antillana (Asteraceae); one new antiproliferative 1,4-naphthoquinone, one known antiproliferative isoflovonoid, and five known antiproliferative stilbenoids from Stuhlmannia moavi (Leguminosae); four known antiproliferative bisbenzylisoquinoline alkaloids from Anisocycla grandidieri (Menispermaceae); one new and two known antiproliferative butanolides, and two new antiproliferative secobutanolides from Ocotea macrocarpa (Lauraceae); one new antiproliferative and five known antiproliferative diterpenoids from Malleastrum rakotozafyi (Meliceae); and 10 known compounds from Monoporus sp. (Myrsinaceae), Premna corymbosa (Verbenaceae), Premna perplexanes (Verbenaceae), Epallage longipes (Asteraceae), and Cinnamosma fragrans (Canellaceae). / Ph. D.

Malaria is a severe and deadly mosquito-borne disease. Although treatable, the continuous emergence of multi-drug resistant parasite strains urgently calls for the development of novel antimalarial agents. P. falciparum parasites synthesize essential isoprenoid precursors, isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), via a non-mevalonate pathway: the methylerythritol phosphate (MEP) pathway. This pathway is not utilized by humans. Thus, compounds that target the MEP pathway and disrupt isoprenoid biosynthesis in P. falciparum hold promise as potent and safe new antimalarial agents, that engage new targets. Previously, we and others identified MMV008138 from the Malaria Box as a MEP pathway targeting compound. Later work revealed that it targets the IspD enzyme within the MEP pathway. Work in the Carlier group has established preliminary structure-activity relationship (SAR) of MMV008138: 1) (1R,3S)-configuration is required; 2) 2', 4'-disubstitution of the D-ring with small, electronegative substituents; 3) functional importance of carboxylate acid at C3. In this work, I aim to gain further insight into the C3 SAR and A-ring SAR of lead compound MMV008138. Synthesized acid bioisosteres and A-ring analogs of MMV008138 were evaluated in their ability to inhibit P. falciparum parasite growth. We showed that the C3 substituent of MMV008138 has a very tight SAR, and likely interacts with a very constricted pocket within the PfIspD enzyme. A-ring modifications are limited to certain positions of MMV001838 and need to be sterically small. However, we have yet to identify a modification that significantly improves drug lead potency. Future work will continue towards understanding the A-ring SAR of MMV008138, as well as D-ring SAR and C1-SAR. Efforts will also be directed towards finding analogs with improved potency, transport and metabolic stability. / MS / Malaria is a severe and deadly mosquito-borne disease, caused by malaria parasites. Although treatable, the continuous emergence of drug resistance urgently calls for the development of novel antimalarial agents. Research in the Carlier group is aimed at finding drug molecules that can selectively target and kill the malarial parasite, and at the same time be safe to humans. The Carlier group has identified MMV008138 from the Malaria Box as a promising drug lead. In this work, I aim to understand the how the structure of MMV008138 play a role in its ability to kill malaria parasites. These results will help identify modification strategies that may significantly improve drug lead potency.

Malaria, a disease caused by members of the Plasmodium genus, remains a threat to global health. Despite the availability of therapeutics, Plasmodium's propensity for generating resistance-conferring mutations threatens the efficacy of these drugs. Therefore, it is essential to develop novel therapeutics, and one approach to discover such compounds is to repurpose current drugs as antimalarials. Human kinase inhibitors, most of which are developed as antineoplastics, are a valuable source of such novel compounds. Human kinase inhibitor research spans over twenty years, generating a wellspring of knowledge regarding compound design, mechanism, and tolerability that can be leveraged in the quest to develop new antiplasmodial drugs. Furthermore, the plasmodial kinome differs substantially from the human kinome, providing opportunities for selectivity and minimization of off-target effects in the host. To this end, we sought to identify and characterize compounds within human kinase inhibitor collections that have antiplasmodial effects. One library yielded a potent polo-like kinase 1 (PLK1) kinase inhibitor, BI-2536, which possessed potent antiplasmodial activity in both the asexual blood stage and liver stage and likely acts through involvement of amino acid starvation. Another library comprised exclusively of type II kinase inhibitors, designed to target kinases in the inactive conformation, produced several interesting lead compounds – TL5-135, YLIU-06-026-1, and the analog pair XMD13-99 and WZ9-034-2. These compounds were highly active against asexual blood stage parasites, killing rapidly while also possessing favorable selectivity and liver stage activity. In vivo, TL5-135 and YLIU-06-026-1 acted prophylactically by preventing infection, and therapeutically by resolving an established infection. Currently, investigations are underway to determine the mechanism of action of the lead compounds and to improve their druglike properties. In whole, this effort has not only yielded promising antiplasmodial compounds, but it also underscores the value of the repurposing approach in the quest for novel antimalarial drugs.

No / Objectives To investigate the metabolism of cryptolepine and some cryptolepine analogues by aldehyde oxidase, and to assess the implications of the results on the potential of cryptolepine analogues as antimalarial agents. Methods The products resulting from the oxidation of cryptolepine and 2-fluorocryptolepine by a rabbit liver preparation of aldehyde oxidase were isolated and identified using chromatographic and spectroscopic techniques. The antiplasmodial activity of cryptolepine-11-one was assessed against Plasmodium falciparum using the parasite lactate dehydrogenase assay. Key findings Cryptolepine was oxidized by aldehyde oxidase give cryptolepine-11- one. Although 2-fluorocryptolepine was found to have less affinity for the enzyme than cryptolepine,it was a better substrate for aldehyde oxidase than the parent compound. In contrast, quindoline, the 11-chloro- , 2,7-dibromo- and 2-methoxy analogues of cryptolepine were not readily oxidized. Cryptolepine-11-one was found to be inactive against P. falciparum in vitro raising the possibility that the effectiveness of cryptolepine as an antimalarial, may be compromised by metabolism to an inactive metabolite by liver aldehyde oxidase. Conclusions Cryptolepine and 2-fluorocryptolepine are substrates for aldehyde oxidase. This may have implications for the design and development of cryptolepine analogues as antimalarial agents.

No / Malaria is a mosquito-borne infectious disease caused by the genus Plasmodium. It causes one million deaths per year in African children under the age of 5 years. There is an increasing development of resistance of malarial parasites to chloroquine and other currently used anti-malarial drugs. Some plant products such as the indoloquinoline alkaloid cryptolepine have been shown to have potent activity against P. falciparum in vitro. On account of its toxicity, cryptolepine is not suitable for use as an antimalarial drug but a number of analogues of cryptolepine have been synthesised in an attempt to find compounds that have reduced cytotoxicity and these have been investigated in the present study in human sperm and lymphocytes using the Comet assay. The results suggest that cryptolepine and the analogues cause DNA damage in lymphocytes, but appear to have no effect on human sperm at the assessed doses. In the context of antimalarial drug development, the data suggest that all cryptolepine compounds and in particular 2,7-dibromocryptolepine cause DNA damage and therefore may not be suitable for pre clinical development as antimalarial agents.

Yes / Dual submicromolar trypanocidal–antiplasmodial compounds have been identified by screening and chemical synthesis of 4-aminoquinoline-based heterodimeric compounds of three different structural classes. In Trypanosoma brucei, inhibition of the enzyme trypanothione reductase seems to be involved in the potent trypanocidal activity of these heterodimers, although it is probably not the main biological target. Regarding antiplasmodial activity, the heterodimers seem to share the mode of action of the antimalarial drug chloroquine, which involves inhibition of the haem detoxification process. Interestingly, all of these heterodimers display good brain permeabilities, thereby being potentially useful for late stage human African trypanosomiasis. Future optimization of these compounds should focus mainly on decreasing cytotoxicity and acetylcholinesterase inhibitory activity.

We have synthesized a series of dimers of (+)-(7R,11R)-huprine Y and evaluated their activity against Trypanosoma brucei, Plasmodium falciparum, rat myoblast L6 cells and human acetylcholinesterase (hAChE), and their brain permeability. Most dimers have more potent and selective trypanocidal activity than huprine Y and are brain permeable, but they are devoid of antimalarial activity and remain active against hAChE. Lead optimization will focus on identifying compounds with a more favourable trypanocidal/anticholinesterase activity ratio.