This thesis is primarily concerned with the investigation of a structure-reactivity relationship in a series of pentacyclic Isodrin derivatives. These compounds undergo a two-hydrogen atom dyotropic rearrangement at vastly differing rates when apparently small structural changes are made. Two pairs of these isomers (with the formulas C(_16)H(_8)Cl(_10) and C(_16)H(_9)Cl(_9) ) have been investigated using both X-ray and neutron single crystal diffraction studies, at ambient and low temperatures. The experimental details of these studies are given for five experiments and the results of the least-squares refinements made using the data from these experiments are reported herein. In addition to conventional crystallographic studies, an experimental charge density study of one of these compounds, C(_16)H(_9)Cl(_9), has been made at 123K. The electron density was modelled using a multipole model which allows explicitly for the aspherical nature of the electron density. The results of this study, including a topological analysis of the charge density are reported in this thesis. The structures of six organometallic, four molybdenum bis(imido) and two half-sandwich niobium imido complexes, are also reported herein. Their structures were determined from single crystal diffraction data. These compounds show the expected structures predicted using the pseudo-isolobal relationship to the Group 4 bent metallocenes of which they may be considered analogues.

A liquid chromatographic technique using ultrastable-Y (US-Y) molecular sieve as the stationary phase and n-pentane as the mobile phase has been developed to fractionate and enrich pentacyclic triterpanes from petroleum. The sieve provides a shape-selective window which distinguishes between the various pentacyclic components, thus fractionating them on the basis of molecular shape differences. This sieving technique has been applied to isolate various pentacyclic triterpanes from sedimentary organic matter to enable better analysis of these biomarkers to be carried out.Biodegraded crude oils from three Australian basins were analysed to assess the geochemistry of their rearranged hopanes. Enhanced abundances of 25-norhopanes, 18(alpha)-30-norneohopane and diahopanes relative to the regular hopanes were observed in the most severely biodegraded samples. Geochemical interpretation of these results suggests that the enhanced abundances are due to the greater resistance of rearranged hopanes to biodegradation compared to regular hopanes. These studies also indicate that enhanced relative abundances of 25-norhopanes in these samples is most likely due to selective bacterial demethylation of (alpha beta)-hopane precursors.A branched and cyclic alkane fraction from a higher plant-derived crude oil was subjected to the US-Y chromatography procedure and the fractions eluted from the column were analysed using GC-MS. The compositions of the first two eluted fractions were markedly different from the initial branched and cyclic alkane mixture in that they were enriched in higher plant-derived triterpanes, such as bicadinanes, spirotriterpane and the oleananes and other, previously unreported, C(subscript)29 and C(subscript)30 triterpanes. A comparison of mass spectral data, GC retention and molecular sieve sorption characteristics of these compounds with those of known ++ / triterpanes of known molecular structure was used to suggest structures for the unknown compounds.Isolation of crude oil fractions enriched in pentacyclic alkanes using the sieving procedure enabled lower concentrations of bicadinanes to be detected than was previously possible by applying selective ion detection GC-MS to branched and cyclic alkane fractions. Application of this technique to a higher-plant derived Jurassic crude oil and two Jurassic sediments from the Eromanga Basin, Australia has revealed the presence of bicadinanes. The occurrence of the cis-cis-trans and trans-trans-trans bicadinane biomarkers that have previously only been reported from angiosperms may indicate an early evolution of flowering plant like species in this basin.The molecular sieving technique has also been used to isolate three pentacyclic triterpanes from low rank coals in order to obtain unambiguous structural identification and to determine their geochemical significance. A major hopanoid component isolated from a Victorian brown coal was characterised by single crystal X-ray diffraction and (subscript)13C NMR spectroscopy as 22R 17(alpha),21(beta)(H)-homohopane. This compound was shown to correspond to the later eluting 17(alpha),21(beta)(H)-homohopane and hence, for the first time, confirmed the common practice of assigning the higher retention time peak in gas chromatograms of (alpha beta) homohopanes as the 22R diastereomer. Heating of the isolated 22R (alpha beta)-homohopane on anthracite produced a mixture of the 22S and 22R diastereomers which implied a product-reactant relationship between the two epimers. Furthermore, a C(subscript)29 and a C(subscript)30 triterpane present in the hydrous pyrolysate of a Bremer Basin coal were also isolated using the molecular sieving procedure. 28 Nor-18(alpha)-oleanane was characterised by single crystal X-ray analysis while lupane was ++ / characterised by (subscript)13C NMR spectroscopy and by co-chromatography with an authentic standard on four different GC phase columns. The unusual occurrence of these triterpanes was attributed to the high sulphur content of the coal.Finally, laboratory isomerisation and reduction of an isomeric mixture of oleanenes was carried out to investigate the origin of oleanane (18(beta)-oleanane) and 18(alpha)-oleanane. Laboratory results indicated that oleanane was mainly derived from olean-18-ene, while 18(alpha)-oleanane was derived from 18(alpha)-olean-12-ene. Analysis of oleanene/oleanane abundances in a sedimentary sequence from Indonesia provided results consistent with laboratory evidence showing that 18(alpha)- olean-12-ene, rather than oleanane, is the main sedimentary precursor of 18(alpha)- oleanane.

Diabetes mellitus (DM) represents a series of metabolic conditions associated with hyperglycemia and caused by defects in insulin secretion, and/ insulin action. Exposure to chronic hyperglycemia may result in microvascular complications in the retina, kidney or peripheral nerves. According to the World Health Organization (WHO) global burden of disease, more than 176 million people are diabetic with about two thirds of these living in developing countries. With a long course and serious complications that often result in high incidences of mobility and mortality rate, the treatment of diabetes is often costly. The management of this disease is not without side effects and this is a challenge to the medical system. This has led the researches to seek new antidiabetic agents from plants. Acetone extract of 8 plants namely Terminalia sericea Burch. Ex DC, Euclea natalensis A.DC, Warbugia salutaris Bertol.f.) Chiov., Artemisia afra Jacq.ex Willd., Aloe ferox Mill, Sclerocarya birrea (A.Richi.) Hochst. subsp. caffra , Spirostachys Africana Sond and Psidium guajava L were evaluated for antidiabetic and antioxidant properties. In addition extracts were tested for cytotoxicity. Different parts of all these plants are traditionally used in South Africa for diabetes treatment. Plants were selected based on ethnobotanical information and phytochemical constituents. For determining inhibitory activity against each enzyme (α-glucosidase and α- amylase), all extracts were tested at concentration that ranged from 2x10-5 to 0.2mg/ml for α-glucosidase and 0.025 to 1.25mg/ml for α-amylase and fifty percent inhibition or higher was taken as significant (p<0.05). The extracts of A. ferox and S. africana showed no inhibition against α-glucosidase at the highest concentration tested (0.2mg/ml) whereas A. afra showed weak inhibition (47.15%). T. sericea showed to be a potent inhibitor of α-glucosidase exhibiting 97.44 % inhibition of the enzyme (p<0.05). W. salutaris, S birrea and E. natalensis also showed good activity on α-glucosidase as they demonstrated 71.84; 97.44 and 92.60 % inhibition respectively (p<0.05). Other plant extracts such as A. ferox and S. africana did not exhibit any activity on α-glucosidase. T. sericea and S. birrea showed the best inhibitory activity on α-amylase enzyme, exhibiting 91.91 and 94.94 % inhibition respectively at 1.25mg/ml. A. afra, E. natalensis, P. guajava and W. salutaris also showed good inhibitory activity on -amylase enzyme at 1.25mg/ml which was the highest concentration tested (p<0.05). Low levels of plasma antioxidants is a risk factor associated with diabetes therefore, it has been suggested that plant-based medicines that contain antioxidant properties add an advantage in curbing complications that arise during DM aetiology. The antioxidant activity of plant extracts was carried out using 2, 2-Diphenyl-1-Picrylhydrazyl (DPPH) assay. Six plant extracts which showed good α-glucosidase and α-amylase inhibitory activity were evaluated for antioxidant activity. The radical scavenging activity was measured in terms of the amount of antioxidants necessary to decrease the initial DPPH absorbance (EC50). The EC50 is the amount of antioxidants necessary to decrease initial DPPH absorbance by 50%. All 6 tested plant extracts showed good activity. W. salutaris and T. sericea demonstrated the highest activity exhibiting EC50 values of 5.08 and 5.56βg/ml respectively as compared to ascorbic acid/Vitamin C (EC50=2.52μg/ml), a well- known potent antioxidant. This was followed by P. guajava (EC50=6.97μg/ml); E. natalensis (EC50=8.46μg/ml) and S. birrea (EC50=9.41μg/ml). A. ferox showed EC50 value of 48.53μg/ml. It has been suggested that plant extracts and compounds must undergo toxicity test for safety before drug discovery is taken into consideration. Due to the large number of plants screened in this study and limited resources in our laboratory, only the acetone extract of T. sericea (which demonstrated good α-glucosidase and -amylase inhibitory activities) was tested for cytotoxicity. Acetone extract of T. sericea demonstrated moderate toxicity against primary vervet monkey kidney cells (VK) cells exhibiting IC50 values of 20.94 μg/ml when tested at 400μg/ml. Consequently, the acetone extract of T. sericea was selected for the isolation and identification of bioactive compounds. A bio-assay guided fractionation of the acetone extract of T. sericea led to the isolation of 4 pure compounds namely β-sitosterol, β-sitosterol-3-acetate, lupeol and 3-onestigmasterol and two sets of mixtures of isomers (epicatechin-catechin; MI1 and epigallocatechingallocatechin; MI2). Antidiabetic, antioxidant and cytotoxicity activities of isolated compounds were evaluated. μ–Sitosterol and lupeol showed best inhibitory activity on α-glucosidase exhibiting 50% inhibitory concentration (IC50) value of 54.50 μM and 66.48 μM respectively (p<0.05). This was followed by the MI2; epigallocatechin-gallocatechin (IC50=119.34 μM); β-sitosterol-3-acetate (IC50=129.34 μM); 3-one-stigmasterol (IC50=164.87 μM) and the MI1; epicatechin-catechin (IC50=255.76 μM). During the evaluation of purified compound’s inhibitory activity on α-amylase, compounds of interest were lupeol and β-sitosterol which exhibited IC50 values of 140.72 μM and 216.02 μM respectively as compared to the positive drug-control acarbose (IC50=65.25 μM). Epicatechincatechin and epigallocatechin-gallocatechin also demonstrated α-amylase inhibitory properties and the IC50 values were found to be lower than 100μg/ml. Epigallocatechin-gallocatechin, epicatechin-catechin and lupeol showed good free radical scavenging activity as they inhibited DPPH by 98.19; 96.98 and 70.90 % at 100ìg/ml respectively (p<0.05). The DPPH scavenging activity was very low in case of 3-one-stigmasterol (21.5% inhibition), whilst β-sitosterol and its derivative β-sitosterol-3-acetate did not show any activity. During cytotoxicity evaluation of pure compounds against monkey kidney cells, all the compounds except β-sitosterol did not inhibit the growth of these cells lines at the highest concentration tested (200μg/ml). β-Sitosterol showed moderate toxicity exhibiting IC50 values of 197.72 μM. β- Sitosterol-3-acetate, epicatechin-catechin, lupeol and epigallocatechin-gallocatechin were found to be non-toxic to Vero cells as 100% cell viability was observed when Vero cells were exposed to these samples at 200μg/ml. The compounds isolated and the extract of T. sericea demonstrated significant antidiabetic and antioxidant properties as compared to well known drugs acarbose (a known -glucosidase and α- amylase inhibitor) and Vitamin C (a well known antioxidant). This study is the first to report α- glucosidase, α-amylase and antioxidant properties of epicatechin-catechin, epigallocatechingallocatechin, β-sitosterol-3-acetate and stigma-4-ene-3-one isolated from T. sericea. In addition, epicatechin-catechin, epigallocatechin-gallocatechin, β-sitosterol-3-acetate and stigma-4-ene-3-one are isolated from T. sericea for the first time. Overall all results scientifically validated the traditional use of the bark of T. sericea for diabetes in South Africa. / Dissertation (MSc)--University of Pretoria, 2011. / Plant Science / unrestricted

Among Nature’s creation, terpenoids are more versatile and exciting natural products. In a remarkable display of synthetic ingenuity and creativity, nature has endowed terpenes with a bewildering array of carbocyclic frameworks with unusual assemblage of rings and functionalities. This phenomenal structural diversity of terpenes make them ideal targets for developing and testing new synthetic strategies for efficient articulation of carbocyclic frameworks. The thesis entitled “Total synthesis of sesquiterpenes acorenols, chamigrenes, and laurokamurene B; and Enantiospecific synthesis of ABC-ring system of A-nor and abeo pentacyclic triterpenes” describes the studies directed towards the total synthesis of the sesquiterpenes mentioned in the title and exploratory studies towards triterpenoids. In each chapter of the thesis, the compounds are sequentially numbered (bold) and references are marked sequentially as superscripts and listed at the end of the chapter. All the spectra included in the thesis were obtained by xeroxing the original NMR spectra. The sesquiterpenes acorenols, containing an interesting spiro[4.5]decane carbon framework, was first isolated in 1970 by the research group of Tomita from the wood of Juniperus rigida. Recently, in 2003, Braun and coworkers reported the isolation of epi α- and epi β-acorenols along with α- and β-acorenols from the sandal wood oil Santalum spicatum. Total synthesis of all the four acorenols has been described in the first part of the first chapter of the thesis. Initially, a model study has been carried out for the spirocyclopentannulation of cyclohexanone employing a combination of Ireland ester Claisen rearrangement and ring closing metathesis reaction to furnish methyl 4-methylspiro[4.5]dec-3-en-1-carboxylate. The same methodology has been extended for the total synthesis of all the four acorenols starting from cyclohexane-1,4-dione via cis and trans isomers of methyl 4-methyl-8-methylene-spiro[4.5]dec-3-ene-1-carboxylate. Total synthesis of β-chamigrene, γ-chamigrene and laurencenone C, containing spiro[5.5]undecane carbon framework, has been described in the second part of the first chapter. As a model study, cyclohexanone has been transformed into 1,5,5-trimethylspiro-[5.5]undec-4-en-3-one employing a combination of Ireland ester Claisen rearrangement and intramolecular type-II carbonyl ene reactions. The methodology has been extended to chamigrenes starting from cyclohexane-1,4-dione via methyl 2-(1-isopropenyl-4-oxocyclo-hexyl)-2-methylpropanoate and 5,5-dimethyl-1,9-ismethylenespiro[5.5]undecan-3-ol. The marine sesquiterpenes laurokamurenes were first isolated in 2006 by Mao and Guo from Laurencia okamurai Yamada. First total synthesis of (±)-laurokamurene B has been described in the first part of the second chapter. To begin with Ireland ester Claisen rearrangement of but-2-enyl 2-methylpropionate furnished methyl 2,2,3-trimethylpent-4-enoate, which was then transformed into 4,5,5-trimethyl-3-(4-methylphenyl)hepta-1,6-dien-3-ol. RCM reaction followed by reductive deoxygeneation transformed 4,5,5-trimethyl-3-(4-methylphenyl)hepta-1,6-dien-3-ol into (±)-laurokamurene B. Subsequently, an enantioselective total synthesis of (+)-laurokamurene B has been accomplished. Stereoselective hydrogenation of methyl campholenoate furnished methyl 2-[(1S,3S)-2,2,3-trimethyl-cyclopent-1-yl]acetate, which was then transformed into (+)-laurokamurene B via degradation of the two carbon side chain and introduction of the aryl moiety, which established the absolute configuration of laurokamurenes. The third chapter deals with the enantiospecific generation of ABC-ring system of A-nor and abeo 4(3 → 2) tetra and pentacyclic triterpenes. To begin with (R)-carvone was identified as B-ring of ABC-ring system of A-nor and abeo tetra and pentacyclic triterpenes, as the absolute configuration at the C-5 position of the targets correlate to the stereo centre of carvone, and isopropenyl group can serve as the C-4 carbon of the targets along with the two gem-dimethyl groups. A lithium liquid ammonia mediated cyclisation of δ,ε-unsaturated esters was employed for the construction of the A ring and an RCM reaction was opted for the construction of the C ring. (R)-Carvone has been converted into 2-(1-ethoxyethoxy)-1,3,7,7-tetramethylbicyclo[4.3.0]non-3-en-8-ol via lithium liquid ammonia mediated cyclisation of methyl 2-(1-ethoxyethoxy)-6-isopropenyl-1,3-dimethylcyclohex-3-enyl]acetate, which was then transformed into 4-methoxymethoxy-2,5,5,9-tetramethyltricyclo[7.4.0.02,6]tridec-11-en-8-one via the RCM reaction of 3,4-bisallyl-8-methoxymethoxy-4,6,9,9-tetramethylbicyclo-[4.3.0]nonan-3-one. The strategy has been further extended to the synthesis of 4-methylene-2,5,5,9-tetramethyltricyclo[7.4.0.02,6]tridec-11-en-8-one, which contains the ABC ring system of abeo 4(3→2) tetra and pentacyclic triterpenes.

FundaÃÃo de Amparo à Pesquisa do Estado do Amazonas / Os efeitos dos triterpenos pentaciclicos &#61537;-amirina e &#61538;-amirina, isolados a partir da resina de Protium heptaphyllum March. (Burseraceae), foram testados preliminarmente em modelos de nocicepÃÃo oral, sendo que &#61538;-amirina apresentou significantes efeitos antinociceptivos, norteando a pesquisa com este isolado na investigaÃÃo de seus efeitos em modelos de dor orofacial induzida por capsaicina ou formalina e na dor induzida por capsaicina na cÃrnea de camundongos; na dor tÃrmica (testes de imersÃo de cauda em Ãgua quente e placa quente); e na nocicepÃÃo visceral induzida por Ãcido acÃtico 0,6%. Camundongos Swiss machos (n = 8 / grupo) foram prÃ-tratados com &#946;-amirina (10, 30 e 100 mg / kg, v.o.), morfina (5 mg / kg, s.c.) ou controle (Ãgua destilada + 0,05% de Tween 80, v.o.), uma hora antes de capsaicina (20 &#61549;L, 1,5 &#61549;g) ou formalina (20&#61549;L/animal) serem administradas na vibrissa direita. &#946;-amirina tambÃm foi avaliada em teste comportamental relacionado à dor, desta vez por aplicaÃÃo tÃpica de capsaicina na conjuntiva do camundongo (âeye wiping testâ). Neste teste foi medido o tempo, em segundos, que o animal passou âlimpandoâ o olho durante um perÃodo de 10 minutos. O triterpenÃide demonstrou principalmente um efeito antinociceptivo dose-independente em todos os modelos de nocicepÃÃo testados. Na dor orofacial induzida por capsaicina, &#61538;-amirina (30 e 100 mg/kg) e morfina foram mais eficazes na reduÃÃo da resposta nociceptiva. Nestas doses, as reduÃÃes foram de 81 e 90% para &#61538;-amirina e 97% para morfina, respectivamente. No modelo de dor orofacial, a nocicepÃÃo produzida pela capsaicina à acompanhada por um aumento na resposta tÃrmica localizada (que foi mensurada por termometria), e reduzida significantemente pelo prÃ-tratamento dos animais com &#61538;-amirina ou L-NAME, um inibidor da NOS. Em animais diabÃticos, a capsaicina injetada na vibrissa promoveu um menor grau de nocicepÃÃo orofacial comparada com os nÃo-diabÃticos. No teste da formalina, morfina e &#946;-amirina apresentaram antinocicepÃÃo significativa reversÃvel nas duas fases por naloxona. No entanto, &#946;-amirina (30 mg/kg) inibiu a segunda fase com maior eficiÃncia. Os valores de DE50 para &#946;-amirina e morfina foram 16,44 mg/kg (LC 10,0-38,41) e 3 mg/kg (LC 2,5-5,0) na primeira fase e 43,37 mg/kg (LC 30,52-39,30) e 3 mg/kg (LC 2,5-5,0) na segunda fase, respectivamente. A co-administraÃÃo de &#946;-amirina e morfina, em seus respectivos nÃveis de dose de DE50, nÃo apresentou qualquer efeito aditivo ou potencializador antinociceptivo. No entanto, as combinaÃÃes das doses DE25 e DE12,5 apresentaram uma antinocicepÃÃo comparÃvel ao efeito combinado da DE50, sugerindo que atravÃs da utilizaÃÃo de &#946;-amirina, a dose analgÃsica de morfina poderia ser minimizada para evitar a sua alta dose e os efeitos colaterais associados. &#946;-amirina tambÃm foi eficaz em aumentar o limiar de dor tÃrmica no teste da imersÃo da cauda (mais nÃo no teste placa quente) e, na reduÃÃo das contorÃÃes induzidas por Ãcido acÃtico. A antinocicepÃÃo produzida por &#946;-amirina, foi significativamente bloqueada em animais prÃ-tratados com os respectivos antagonistas vermelho de rutÃnio (2 mg/kg, s.c.) e naloxona (1 mg/kg, i.p.), indicando o envolvimento de receptores da capsaicina (TRPV1) e opiÃides em seu mecanismo. No teste da formalina, de forma similar à morfina, &#946;-amirina bloqueou significativamente a inibiÃÃo da ingestÃo alimentar associada a dor. Assim como morfina, &#946;-amirina apresentou aÃÃo inibitÃria sobre o trÃnsito intestinal, efeito esse revertido pelo prÃ-tratamento com antagonista opiÃide nÃo seletivo, naloxona. Estes dados sugerem que &#946;-amirina apresenta um potencial antinociceptivo comparÃvel à analgesia perifÃrica produzida pela morfina, evidencia a exploraÃÃo desta para o desenvolvimento de um analgÃsico nÃo-opiÃide Ãtil na farmacoterapia de patologias do trigÃmeo e visceral. / The effects of pentacyclic triterpene &#946;-amiryn and &#946;-amyrin, isolated from resin of Protium heptaphyllum March. (Burseraceae), were preliminarily showed significant tested in models of nociception oral, and antinociceptives effects, guiding the search with this isolate in the investigation of their effects in models of orofacial pain induced by capsaicin or formalin and against capsaicin-induced corneal pain; thermal pain (tail immersion test in hot water and hot-plate) and in acetic acid 0,6%-induced visceral nociception in mice. Male Swiss mice (n = 8 per group) were pre-treated with &#946;-Amyrin (10, 30, and 100 mg/kg, p.o.), morphine (5 mg/kg, s.c.) or vehicle (distlled water + 0,05% Tween 80), one hour before the capsaicin (20 &#956;l, 1.5 &#956;g) or formalin (20 &#956;l, 1.5%) injection into the right vibrissa. &#946;-Amyrin was also assessed on pain-related behavioral test (Eye-wiping) by topical application of capsaicin (20 &#956;l, 1.5 &#956;g) on to the mouse conjuctiva and the time (sec) that the animal spent in eye wiping was determined during a 10 min period. The triterpenoid demonstrated mostly a dose-unrelated antinociception in all the test models of nociception. Against the orofacial pain induced by capsaicin, &#946;-Amyrin (30 e 100 mg/kg, p.o.) and morphine showed greater potency in reducing the nociceptive response. At the doses employed, the reductions were 81 and 90% to &#946;-Amyrin and 97% for the morphine, respectively. Capsaicin nociception in orofacial test is accompanied by a localized thermal flare (measured by thermometry), which was significantly diminished by pretreatment of animals with &#946;-Amyrin or L-NAME, an NOS inhibitor. In four weeks diabetic mice, capsaicin injected into vibrissa pad demonstrated a lesser degree of orofacial nociception compared to non-diabetics. In formalin test, both morphine and &#946;-Amyrin showed significant naloxone reversible antinociception in both phases. However, &#946;-Amyrin inhibited the second phase response, more prominently, at 30 mg/kg. The caliculated ED50 values for &#946;-Amyrin and morphine were 16,44 mg/kg (CL 10,0 - 38,41) and 3 mg/kg (CL 2,5 - 5,0) in the first phase and 43,37 mg/kg (CL 30,52 - 39,30) and 3 mg/kg (CL 2,5 - 5,0) in the second phase, respectively. Co-administration of &#946;-Amyrin and morphine at their respective ED50 dose levels failed to demonstrate any additive or potentiating effect on anti-nociception. However, at ED25 and ED12.5 dose-combinations exhibited an antinociception that equalled their ED50 combination effect, suggesting that by the use of &#946;-Amyrin, the analgesic dose of morphine could be minimised to avoid its high-dose-associated side-effects. Similar to morphine, &#946;-Amyrin significantly blocked the pain-related suppression of food intake in formalin test. &#946;-Amyrin (30 and 100 mg/kg was also effective in increasing the thermal pain threshold in hot-water tail immersion test (but not in hot-plate test), and in reducing the acetic acid-induced writhes. The antinociception produced by 30 mg/kg &#946;-Amyrin was significantly blocked in animals pre-treated with the respective antagonists capsazepine (5 mg/kg, s.c.), and naloxone (1 mg kg/kg, i.p.), indicating the involvement of capsaicin (TRPV1) and opioid receptors in its mechanism. Like morphine, &#946;-Amyrin showed an inhibitory effect on intestinal transit, an effect reversed by pretreatment with nonseletive opiÃide antagonist, naloxona. These data indicate that &#946;-Amyrin has the antinociceptive potential comparable to peripheral analgesia produced by morphine that could be explored further on its suitability in developing a non-opioid analgesic useful in pharmacotherapy of trigeminal and visceral pathologies.

Le manque de thérapies innovantes en chimiothérapie humaine incite la communauté scientifique à s'intéresser à de nouvelles sources de composés bioactifs. Nous pouvons citer les métabolites secondaires de plantes, auxquels appartiennent les acides hydroxy pentacycliques triterpénoiques (AHPTs) et plus particulièrement les Acides Ursolique (AU), Oléanolique (AO) et Bétulinique (AB). Ces molécules font l'objet de nombreuses études qui tendent à démontrer leurs propriétés : anti-infectieuses, anticancéreuses, antiprolifératives, anti-inflammatoires, hépatoprotectrices. Le principal obstacle à leur utilisation à des fins thérapeutiques, reste l'insolubilité de ces AHPTs dans l'eau. L'objectif de ce travail a donc été d'augmenter leur hydrosolubilité. Dans un premier temps, en accord avec les recommandations et/ou normes existantes, nous avons démontré que le spectre d'activité antibactérienne de l'AU et de l'AO se limitait aux bactéries à Gram positif. Aucun AHPT n'a montré d'activité antifongique. Seul l'AB a montré une activité intéressante sur le Cytomégalovirus humain (hCMV) ; aucune activité antivirale n'ayant été retrouvée sur le Poliovirus. Enfin, l'AB, mais encore plus l'AU ont montré une activité anticancéreuse à l'encontre de cellules modèles de leucémie myéloïde chronique (LMC). Dans un deuxième temps, nous avons procédé à la fabrication et à l'étude de complexes entre les AHPTs et des cyclodextrines. Nous avons retenu la gamma-cyclodextrine (gamma-CD), qui présentait l'avantage de complexer les 3 AHPTs avec une constante de formation « moyenne » à « élevée ». Ces complexes AHPTs :gamma-CD ont été caractérisés en utilisant diverses techniques : chromatographiques, thermiques et spectrométriques. Nous avons conclu à l'obtention de complexes d'inclusion qui ont permis d'augmenter la solubilité des AHPTs. Dans une dernière partie, nous avons évalué les activités biologiques des complexes AHPTs : gamma-CD. Les résultats montrent que les complexes AU : gamma-CD et AO : gamma-CD restent actifs à l'encontre des bactéries à Gram positif (mais avec une efficacité plus faible) ; tandis que le complexe AB : gamma-CD se révèle être actif sur certaines bactéries. Le complexe AB : gamma-CD, et de façon surprenante le complexe AU : gamma-CD présentent une activité antivirale à l'encontre du hCMV. Enfin, la diminution de la cytotoxicité liée à la complexation des AHPTs accroit l'intérêt des molécules d'AU et d'AB sur les cellules de LMC / The lack of innovative therapies in human chemotherapy incites the scientific community to be interested in new sources of bioactive compounds. We can quote the secondary metabolites of plants, to which belong hydroxy pentacyclic triterpene acids (HPTAs) and more particularly Ursolic (UA), Oleanolic (OA) and Betulinic Acids(BA). These molecules are the subjetc of numerous studies which tend to demonstrate their properties: anti-infective, anticancer, antiproliferatives, anti-inflammatory and hepatoprotectrive. The main obstacle to their use in therapeutic purposes stays the insolubility of these AHPTs in the water. Thus the objective of this work was to increase their hydrosolubility. At first, in agreement with the recommendations and/or the existing standards, we demonstrated that the antibacterial spectra of UA and OA are limited to Gram-positive bacteria. No HPTA showed antifungal activity. Only the BA showed an interesting antiviral activity on human Cytomegalovirus (hCMV); no antiviral activity was on Poliovirus. Finally, the BA, but even more UA showed an anticancer activity against cellular model of chronic myeloid leukemia (CML). Secondly, we proceeded to the manufacturing and to the study of complexes between HPTAs and cyclodextrines. We retained gamma-cyclodextrine (gamma-CD), which presented the advantage to complex the 3 AHPTs with a constant of "average" to "raised". These HPTAs:gamma-CD complexes were characterized by using diverse techniques: chromatographic, thermal and spectrometric. We concluded in the obtaining of inclusion complexes which allowed increasing the solubility of the HPTAs. In a last part, we estimated the biological activities of the HPTAs:gamma-CD complexes. The results show that the UA:gamma-CD and OA:gamma-CD complexes remain active against Gram-positive bacteria (but with a weaker efficiency); whereas the BA:gamma-CD complex shows to be active on certain bacteria. The BA:gamma-CD complex, and in a surprising way the UA:gamma-CD complex presents an antiviral activity against the hCMV. Finally, the decrease of the cytotoxicity linked to the complexation of the HPTAs believes the interest of UA and of BA on CML cells

Les pathologies infectieuses, maladies causées par certains micro-organismes pathogènes parmi les bactéries, les virus, les champignons et les protozoaires, sont à l’origine des taux de mortalité et de morbidité élevés enregistrés surtout dans les pays en voie de développement où la majorité de la population n’a pas les moyens d'accéder aux soins de santé. Les résistances des micro-organismes aux antimicrobiens, observées actuellement dans la pratique médicale moderne, constituent un autre grand problème lié au traitement de ces maladies. Elles constituent l’une des menaces de santé les plus sérieuses et peuvent frapper n’importe qui dans le monde. Face à ces fléaux, il est urgent de découvrir de nouveaux agents antimicrobiens qui pourraient, éventuellement, présenter de nouveaux mécanismes d'action. Une bonne part des plantes utilisées en médecines traditionnelles contiennent des composants antimicrobiens utiles contre les infections et qui peuvent aider dans la lutte contre les maladies infectieuses liées à l’antibiorésistance. C’est dans cette optique que nous avons mené une enquête ethnobotanique sur les plantes médicinales utilisées contre les infections microbiennes en médecine traditionnelle Burundaise. Nous en avons inventorié 155 et sélectionné 5 d'entre elles (Justicia subsessilis Oliv. (Acanthaceae); Platostoma rotundifolium (Briq.) A. J. Paton (Lamiaceae), Virectaria major (Schum.) Verdc. (Rubiaceae), Pavetta ternifolia (Oliv.) Hiern (Rubiaceae), et Stomatanthes africanus (Oliv. & Hiern) R. M. King & H. Rob. (Asteraceae)) pour en étudier la composition phytochimique et les propriétés biologiques. Les extraits de ces plantes ont été évalués notamment pour leurs effets antibactériens direct (bactéricide ou bactériostatique) et indirect (modulation des mécanismes de résistance qui augmente ou restaure l’activité des antibiotiques sur des souches résistantes). Les cinq plantes retenues ont montré une activité antibactérienne, justifiant ainsi leur usage contre les infections microbiennes en médecine traditionnelle Burundaise et, plus particulièrement, l’espèce Platostoma rotundifolium, dont les extraits ont montré des effets antibactériens directs et indirects sur des souches sensibles et résistantes. Les extraits de Platostoma rotundifolium ont également présenté des effets sur l’expression de gènes (lasB et rhlA) impliqués dans le quorum sensing, et sur la formation du biofilm de Pseudomonas aeruginosa PAO1. En vue d’isoler et identifier les molécules responsables de ces différentes activités, l’extrait acétate d’éthyle (le plus actif) de Platostoma rotundifolium a été soumis à un fractionnement bioguidé. Celui-ci a permis d’isoler neuf composés qui ont été identifiés comme étant les acides ursolique, corosolique, tormentique, hyptadiénique, et 2α, 3α, 19β-trihydroxyurs-12-èn-28-oïque (isolé pour la première fois lors de ce travail et auquel nous avons donné le nom d’acide jérémique), le squalène, le cassipourol, le β-sitostérol et l’α-amyrine. Toutes ces molécules sont isolées pour la première fois de Platostoma rotundifolium. Les trois premiers composés ont présenté un effet bactéricide sur les souches bactériennes sensibles et résistantes, tandis que les trois derniers ont montré une action inhibitrice significative de l’expression de gènes (lasB et rhlA) impliqués dans le quorum sensing et de la formation de biofilm de Pseudomonas aeruginosa PAO1. Toutes ces molécules actives peuvent constituer une voie dans la lutte contre les maladies infectieuses et l’antibiorésistance; nous pouvons conclure que les données issues d’une enquête ethnobotanique sur les savoirs et les savoir-faire des guérisseurs traditionnels sont très importantes, surtout lorsqu’elles sont exploitées jusqu’à la détermination des principes actifs responsables d'une activité pharmacologique donnée. / Infectious pathologies are diseases caused by the transmission of some pathogenic microorganisms among bacteria, viruses, fungi and protozoa. They drive the high mortality and morbidity rates recorded especially in developing countries, where the majority of the population cannot afford to access health care. The antimicrobial resistances currently observed in modern medical practice represent another major problem in the treatment of these diseases. These resistances are one of the most serious population health threats and can strike anyone in the world. It has thus become urgent to discover new antimicrobial agents that could possibly have novel mechanisms of action.Many plants used in traditional medicines against infections harbor useful antimicrobial components that can help in the fight against infectious diseases and antibiotic resistances. In this context, we conducted an ethnobotanical survey of medicinal plants used in Burundian traditional medicine to treat microbial infections. We inventoried 155 herbs from which 5 (Justicia subsessilis Oliv. (Acanthaceae); Platostoma rotundifolium (Briq.) A. J. Paton (Lamiaceae), Virectaria major (Schum.) Verdc. (Rubiaceae), Pavetta ternifolia (Oliv.) Hiern (Rubiaceae), and Stomatanthes africanus (Oliv. & Hiern) R. M. King & H. Rob. (Asteraceae) were selected for phytochemical screening and biological assays. The extracts of these plants were evaluated for their antibacterial effects, direct (bacteriostatic or bactericidal) and indirect (inhibition of resistance mechanisms by increasing or restoring the activity of antibiotics against resistant strains). All the selected plants species have shown antibacterial activity, justifying their use against microbial infections in Burundian traditional medicine, and more particularly Platostoma rotundifolium, whose extracts showed direct and indirect antibacterial effects on susceptible and resistant (MRSA) strains. The extracts from Platostoma rotundifolium also presented inhibitory effects on the expression of genes involved in quorum sensing, lasB and rhlA, as well as on biofilm formation by Pseudomonas aeruginosa PAO1.In order to isolate and identify the molecules responsible for these activities, the ethyl acetate extract (most active) from Platostoma rotundifolium was submitted to bioguided fractionation. This led to the isolation of nine compounds that were identified as ursolic acid, corosolic acid, tormentic acid, hyptadienic acid and 2α, 3α, 19β-trihydroxyurs-12-en-28-oic acid (isolated for the first time during this work and that was named jeremic acid), squalene, cassipourol, β-sitosterol and α-amyrin. All these molecules were isolated for the first time from Platostoma rotundifolium. The first three compounds showed a bactericidal effect on sensitive and resistant strains of bacteria, while the last three showed significant inhibitory effects on the expression of two QS genes (lasB and rhlA), and on biofilm formation by Pseudomonas aeruginosa PAO1. All these active molecules can be a lead in the fight against antibiotic resistance; and we can conclude that the data from an ethnobotanical survey of the knowledge and skills of traditional healers are very important, especially when they are exploited until the determination of the active ingredients responsible for a specific pharmacological activity. / Doctorat en Sciences biomédicales et pharmaceutiques (Pharmacie) / info:eu-repo/semantics/nonPublished