• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 46
  • 33
  • 6
  • 6
  • 5
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 97
  • 28
  • 15
  • 14
  • 10
  • 10
  • 9
  • 8
  • 8
  • 8
  • 7
  • 7
  • 7
  • 7
  • 7
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Synthetic studies of zoapatanol: construction of the oxepane system by intramolecular nitrile oxide and/or nitrone cycloaddition.

January 1993 (has links)
by Ching-hung Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 75-78). / Chapter i --- Biography / Chapter ii --- Abstract / Chapter iii --- Acknowledgments / Chapter iv --- Abberivations / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Review on the published syntheses of Zoapatanol --- p.1 / Chapter 1.2 --- Review on the construction of the oxepane ring --- p.7 / Chapter 1.3 --- "Review on the intramolecular nitrone and nitrile oxide 1,3-dipolar cycloaddition" --- p.15 / Chapter 1.3.a. --- Nitrone-olefin cycloaddition --- p.16 / Chapter 1.3.b. --- Nitrile-oxide-olefin cycloaddition --- p.17 / Chapter 1.4 --- Isoxazoline Transformation --- p.18 / Chapter Chapter 2 --- Results and Discussion / Chapter 2.1 --- General Aspect --- p.19 / Chapter 2.2 --- "Entries to 6 and 7-membered O-heterocycles via 1,3-dipolar nitrone cycloaddition" --- p.21 / Chapter 2.3 --- "Entries to 6 and 7-membered O-heterocycles via l,,3-diploar nitrile oxide cycloaddition" --- p.33 / Chapter 2.4 --- Conclusion --- p.47 / Chapter Chapter 3 --- Experimental / General --- p.49 / Experimental --- p.51 / References --- p.75
42

The molecular mechanism of mitotic arrest induced by a novel diterpenoid pseudolaric acid B and a novel gene encoding RNA-binding protein 22

Wong, Kam-wai. January 2006 (has links)
Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.
43

Studies on the Secondary Metabolites from the Soft Coral Lobophytum durum

Chen, Hwa-Pyng 21 June 2011 (has links)
Soft corals of the genus Lobophytum (Alcyoniidae) have been well recognized as a rich source of various secondary metabolites that have attracted much interest for the natural products chemists due to their structural complexity and remarkable pharmacological activities such as cytotoxicity, antibacterial activities, anti-inflammatory properties, and antiviral activity. Twelve cembrane diterpenes including six new secondary metabolites 1−6 were isolated organic extracts of soft coral Lobophytum durum collected at Dongsha Atolls. The structures of these six new cembranolides were determined by 1H, 13C, DEPT, COSY, HMBC, HSQC, NOESY, IR and Mass spectra. Furthermore, these six new secondary metabolites 1−6 were evaluated in vitro for the cytotoxicity against A-459 (human lung carcinoma), HT-29 (human colon adenocarcinoma), and P-388 (mouse lymphocytic leukemia) cancer cell lines, and antiviral activity against HCMV (human cytomegalovirus) cells.
44

Structure elucidation and oxidation chemistry of natural products

施麗琼, Sy, Lai-king. January 1998 (has links)
published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy
45

Studies in marine diterpene chemistry /

Van Wyk, Albert Wynand Wincke. January 2007 (has links)
Thesis (Ph.D. (Chemistry)) - Rhodes University, 2008.
46

New nitrogenous spongian diterpenes from the New Zealand marine sponge Darwinella oxeata : a thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Master of [Science] in Chemistry /

Dowle, Katie Orlagh. January 2008 (has links)
Thesis (M.Sc.)--Victoria University of Wellington, 2008. / Includes bibliographical references.
47

Contribuição ao Conhecimento Químico de Plectranthus ornatus Codd / Contribution to the Chemical Knowledge of Plectranthus ornatus Codd

Ávila, Fábio do Nascimento January 2015 (has links)
ÁVILA, Fábio do Nascimento. Contribuição ao Conhecimento Químico de Plectranthus ornatus Codd. 2015. 151 f. Dissertação (Mestrado em Química)–Universidade Federal do Ceará, Fortaleza, 2015. / Submitted by Celia Sena (celiasena@dqoi.ufc.br) on 2017-06-16T18:33:35Z No. of bitstreams: 1 2015_ dis_fnavila.pdf: 8358015 bytes, checksum: 6414d982f4eaeaa80a3994de2cb4d389 (MD5) / Approved for entry into archive by Jairo Viana (jairo@ufc.br) on 2017-06-29T20:07:36Z (GMT) No. of bitstreams: 1 2015_ dis_fnavila.pdf: 8358015 bytes, checksum: 6414d982f4eaeaa80a3994de2cb4d389 (MD5) / Made available in DSpace on 2017-06-29T20:07:36Z (GMT). No. of bitstreams: 1 2015_ dis_fnavila.pdf: 8358015 bytes, checksum: 6414d982f4eaeaa80a3994de2cb4d389 (MD5) Previous issue date: 2015 / The present work describes the phytochemical and pharmacological study of aerial parts of Plectranthus ornatus Codd (Lamiaceae), cultivated at Horto de Plantas medicinais da Universidade Federal do Ceara-UFC. P. ornatus is a native plant from India, introduced in Brazil during the age of great navigations and used by the folks as a relief and treatment of digestive and respiratory problems by the name of boldo-gambá, boldo pequeno and novalgina. The hexane extract of aerial parts of P. ornatus were submitted to successively chromatographic process, including High Performance Liquid Chromatography (HPLC), obtained eleven (11) chemical compounds belonging to diterpene class, which five (05) are described for the first time on literature and named as: Methyl-11R-acetoxyneocleroda-3,13E-dien-15-oic, 11R-acetoxy-3,4-dihydroxyneocleroda-13E-en-15-oic acid, 11R-acetoxysolidagonal acid, 11R-acetoxy-solidago-3,15-dioic acid, Pseudo-coleon R and 11R-acetoxyneocleroda-2,4(18), 13E-trien-15-oic acid, together with six (06) known compounds: Plectrornatin A, Coleon R, ent-labd-13-en-8β-ol-15-oic acid, 11R-acetoxy-3β-hydroxyneocleroda-4(18), 13E-dien-15-oic acid and 11R-acetoxy-2-oxo-neocleroda-3,13E-dien-15-oic acid. The structure determination of all secondary metabolites isolated was performed by spectrometric techniques such as hydrogen-1 and carbon-13 nuclear magnetic resonance (1H NMR and 13C one/two- dimensional), infrared spectrometry (IR), high resolution mass spectrometry and comparison with literature data. Cytotoxic activity of compounds was evaluated against four different human cancer cell lines: HCT-116 (colon adenocarcinoma), HL-60 (leukemia), OVCAR-8 (ovarian carcinoma) and SF-295 (glioblastoma). The cell cultures were regularly maintained at logarithmic phase of growth. IC50 values were determined using the MTT assay and measured IC50 values along with 95% confidence. / O presente trabalho intitulado CONTRIBUIÇÃO AO CONHECIMENTO QUÍMICO DE Plectranthus ornatus Codd, descreve o estudo fitoquímico e farmacológico das partes aéreas de P. ornatus Codd (Lamiaceae), cultivado no Horto de Plantas medicinais da Universidade Federal do Ceara-UFC. P. ornatus é uma espécie nativa da índia e introduzida no Brasil no período das grandes navegações, sendo comumente utilizado na medicina popular para o alívio e tratamento de enfermidades relacionadas ao trato digestivo e aparelho respiratório, sob o nome popular de boldo-gambá, boldo pequeno e novalgina. O estudo fitoquímico do extrato hexânico das partes aéreas de P. ornatus foi submetido a inúmeras técnicas cromatográficas, incluindo Cromatografia Líquida de Alta Eficiência (CLAE), resultando no isolamento de 11 constituintes químicos pertencentes à classe dos diterpenos, dos quais 05 (cinco) estão sendo relatados pela primeira vez na literatura e nomeados como: 11R-acetoxineocleroda-3,13E-dien-15-oato de metila, Ácido 11R-acetoxi-3,4-dihidroxineocleroda-13E-en-15-óico, Ácido 11R-acetoxisolidagonal, Ácido 11R-acetoxi-solidago-3,15-dióico e Ácido 11R-acetoxineocleroda-2,4(18), 13E-trien-15-óico, juntamente com os metabólitos já conhecidos: Plectrornatina A, Coleon R, Ácido ent-labd-13-en-8β-ol-15-oico, Ácido 11R-acetoxi-3β-hidroxineocleroda-4(18), 13E-dien-15-oico e Ácido 11R-acetoxi-2-oxo-neocleroda-3,13E-dien-15-oico. A determinação estrutural de todos os metabólitos secundários isolados foi realizada através do emprego de técnicas espectrométricas como ressonância magnética nuclear de hidrogênio-1 e carbono-13 (RMN de 1H e de 13C uni e bidimensionais), espectroscopia na região do infravermelho (IV), espectrometria de massas de alta resolução, obtida com ionização por electrospray e comparação com dados da literatura. As moléculas obtidas foram testadas frente à atividade citotóxica contra 04 (quatro) linhagens de células cancerígenas: HCT-116, OVCAR-8, HL-60 eSF-295, utilizando o método de análise colorimétrica baseada na conversão do sal 3-(4,5-dimetil-2-tiazol) - 2,5-difenil-brometo de tetrazolium (MTT) que permite a quantificação indireta da porcentagem de células vivas.
48

AvaliaÃÃo do potencial genotÃxico e mutagÃnico do Ãcido caurenÃico, um diterpeno isolado da planta Copaifera langsdorffi Desf. (LEGUMINOSAE) / Genotoxic and mutagenic assessment of kaurenoic acid, a diterpene isolated from Copaifera langsdorffii

Bruno CoÃlho Cavalcanti 14 December 2006 (has links)
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Kaurenoic acid (KA) is a diterpene presents in the oil-resin (copaiba oil) from plants belongs to Copaifera spp. As copaiba oil, KA also displayed a great variability of medicinal applications. In the present study, the genotoxic and mutagenic potential of KA from Copaifera langsdorffii on human lymphocytes, human leukemia cells (HL60) and bone marrow cells was evaluated. KA did not show selective action between lymphocytes and leukemia cells, has been induced apoptosis and DNA damage at same magnitude as valuated by bromide etidium/orange acridine and comet assay. Due to this observation, lymphocytes were selected for further experiments. According with comet assay results, more than 80% of lymphocytes DNA damage was repaired after 48 hours post-treatment. Lymphocytes treated with KA (30 and 60Âg/mL) showed increases on micronucleus frequencies in relation to negative control group. On the chromosome aberration test, lymphocytes treated at phse G1 and transition phase G1/S showed great sensibility (cytotoxicity and chromosomes aberrations) in comparison to cells treated at another phases of cell cycle. After treatment, any increase of polyploidy cells number was noted. Mices were treated with KA (25, 50 and 100mg/kg), and after 24 and 48 hours, they were sacrificed afterwards with the medulla extraction. This material was submitted to chromosomal damage observations (microniclei) in polychromatic erythrocytes (PCE). A great occurrence of micronucleated PCE was noted only at animals groups sacrificed 24 hours after treatment. The rate between PCE and NCE (normochromatic erythrocytes) was lower for animals sacrificed later. These observations indicating toxicity effects on the bone marrow cells. The mutagenic assay with yeast Saccharomyces cereviseae showed that the cytotoxic and mutagenic effects of KA were more pronounced during exponential growth phase, when the access to DNA is facilitated. KA induced locus and frameshift mutations. Frameshift mutations induced by DNA-intercalanting drugs have been correlated with DNA strand breaks induced by inhibition of DNA topoisomerases. On the DNA relaxation assay, KA inhibited the action of topoisomerase I. This inhibition effect seens to be related to the intercalanting ability of kaurenoic acid between DNA bases of pair. Thus, DNA strand breaks, the occurrence of micronucleated cells and frameshift mutations could be explained by the intercalanting action of kaurenoic acid. And the absence of polyploidy cells suggests that kaurenoic acid did not interfere on mitotic apparatus of cell. In conclusion, kaurenoic acid showed genotoxic and mutagenic effects on all the assays used / O Ãcido caurenÃico (AC) à um diterpeno presente no Ãleo resinoso de espÃcies de Copaifera. Assim como o Ãleo resinoso, o AC tambÃm apresenta uma ampla variabilidade de aplicaÃÃes medicinais. O presente trabalho teve como objetivo avaliar o potencial genotÃxico e mutagÃnico do AC isolado da planta Copaifera langsdorffii em linfÃcitos, cÃlulas leucÃmicas HL60 e em cÃlulas da medula Ãssea de camundongos. O AC nÃo mostrou seletividade entre linfÃcitos e HL60 tendo induzido apotose e danos ao DNA na mesma intensidade, avaliados pela coloraÃÃo diferencial por brometo de etÃdio/acridina laranja e pelo teste do cometa, respectivamente. De acordo com o teste do cometa, mais de 80% dos danos induzidos ao DNA de linfÃcitos foi reparada 48 horas apÃs o tratamento. LinfÃcitos tratados com AC apresentaram aumento, siginificativo, na freqÃÃncia de micronÃcleos e maior sensibilidade (citotoxicidade e aberraÃÃes cromossÃmicas) nas fases G1 e G1/S do ciclo celular, sem induzir aumento no nÃmero de cÃlulas poliplÃides. Camundongos foram tratados com AC nas doses de 25, 50 e 100mg/kg e apÃs 24 e 48 horas sacrificados, sendo, posteriormente, extraÃda a medula Ãssea, e o material submetido Ãs observaÃÃes de perdas cromossÃmicas (micronÃcleos) em eritrÃcitos policromÃticos. Uma maior incidÃncia de micronÃcleos ocorreu no grupo de animais sacrificados 24 horas apÃs o tratamento. A avaliaÃÃo da razÃo entre eritrÃcitos policromÃticos e normocromÃticos, foi menor para os animais sacrificados 48 horas apÃs o tratamento, indicando toxicidade em cÃlulas da medula. Nos ensaios de mutagÃnese com a levedura Saccharomyces cerevisea, o efeito citotÃxico e mutagÃnico do AC foi mais acentuado durante o crescimento exponencial da levedura, no qual o DNA està mais acessÃvel ao composto. O AC induziu mutaÃÃes lÃcus especÃficas e de deslocamento do quadro de leitura. MutaÃÃes do tipo deslocamento do quadro de leitura tendem a serem induzidas por agentes intercalantes de DNA e tÃm sido correlacionadas com as quebras de fitas de cadeia de DNA induzidas pela inibiÃÃo da aÃÃo de topoisomerase. No teste de relaxamento do DNA, o AC inibiu a aÃÃo da topoisomerase I. A inibiÃÃo da aÃÃo da topoisomerase I parece estar relacionada à intercalaÃÃo do AC no DNA. Assim, as quebras de fitas no DNA e induÃÃo de micronÃcleos e mutaÃÃes de deslocamento do quadro de leitura, podem estar relacionadas à aÃÃo intercalante do Ãcido caurenÃico. A ausÃncia de cÃlulas poliplÃides sugere que o Ãcido caurenÃico nÃo interfere no aparelho mitÃtico da cÃlula. Em conclusÃo, o Ãcido caurenÃico apresenta potencial genotÃxico e mutagÃnico nos modelos estudados.
49

Studies in marine diterpene chemistry

Van Wyk, Albert Wynand Wincke January 2008 (has links)
This thesis comprises both a natural product investigation and a synthetic component. The natural product investigations are presented in Chapters Two and Three. In Chapter Two the isolation and spectroscopic identification of the new isocopalane diterpene 12S,13R,14Sisocopalan- 13-ol-12,14-diacetate (2.1) and two known 3-(14S)-isocopal-12-ene-15-oyl-1- acetyl-sn-glycerol (2.2) and 3-(14S)-isocopal-12-ene-15-oyl-2-acetyl-sn-glycerol (2.3) from a single, large, unidentified sub-Antarctic nudibranch, collected near Marion Island, approximately 2000 km south of Cape Town are described. Chapter Three discusses the isolation, spectroscopic structure elucidation and anti-oesophageal cancer activity (3.1-3.4 only) of two known labdane diterpenes 6β,7α-diacetoxylabda-8,13E-dien-15-ol (3.1) and 2α,6β,7α-triacetoxylabda-8,13E-dien-15-ol (3.2) and one new 6β,7α,15-triacetoxylabda 8,13E-diene (3.3), as well as new 3α,11-dihydroxy-9,11-seco-cholest-4,7-dien-6,9-dione (3.4) and cholest 7-en-3,5,7-triol (3.5) from the endemic pulmonate mollusc, Trimusculus costatus. The absolute configuration of 3.2, and hence 3.1 and 3.3 (from biogenetic arguments) was determined through X-ray diffraction of a single crystal of the camphanate ester of 3.2. The absolute configuration of the secondary hydroxyl at C-3 of 3.4 was established using the Modified Mosher’s method. The synthetic component of the thesis commences in Chapter Four with the semi-synthesis of labdane diterpene nitriles 9α-cyano-15,16-epoxy-7β-hydroxylabda-13(16),14-dien-6-one (4.1), 9α-cyano-15,16-epoxy-7-hydroxylabda-7,13(16),14-trien-6-one (4.2) and 9α-cyano-15,16- epoxy-6β,7β dihydroxylabda-13(16),14-diene (4.3) from the terrestrial labdane diterpene, hispanolone (4.4). This work is an extension of previous synthetic studies directed towards the synthesis of T. costatus metabolites. Diterpenes 4.1-4.3 exhibited in planta activity against the economically important crop pathogens, Magnaporthea grisea and Puccinia recondita. Chapter Five describes the successful semi-synthesis of two isomeric marine molluscan labdane diterpene aldehyde metabolites, labd-13E-ene-8β-ol-15-al (5.1) and labd-13Z-ene- 8β-ol-15-al (5.2) from the commercially available, terrestrial plant derived, labdane diterpene manool (5.3). Diterpenes 5.1 and 5.2, originally isolated from the Mediterranean nudibranch,Pleurobranchaea meckelii and selected diterpenes arising from this synthesis were evaluated for their activity against an oesophageal cancer cell line (WHCO1). Chapter Six further develops the research discussed in Chapter Five, where ethyl 17-norabiet-13(15)-E-en-8β-ol- 16-oate (5.49) and ethyl 17-norabiet-13(15)-Z-en-8β-ol-16-oate (5.50) were first semisynthesized serendipitously. Based on their structural relationship to naturally occurring tricyclic diterpenes with anti-plasmodial activity, tricyclic diterpenes, 17-norpimaran-13α- ethoxy-8,16-olactone (6.6), 17-norisopimar-15-ene-8β,13β-diol (6.7), 17-norisopimarane- 8β,16-diol (6.8) and 17-norabiet-13(15)-ene-8β,16-diol (6.9) were semi-synthesized from the terrestrial labdane diterpene, 5.3, and critically evaluated for their antimalarial potential from parasite inhibition and haemolytic studies.
50

Structural and synthetic investigations of diterpenoid natural products from southern African marine invertebrates

Gray, Christopher Anthony January 2003 (has links)
This thesis is divided into two parts. The first part (Chapter Two) documents a bioassay guided investigation of the ethyl acetate extracts of four marine invertebrates from Mozambique (an Irciniid sponge, a Haliclona sp. sponge, an ascidian tentatively identified as Diplosoma sp., and the soft coral Cladiella kashmani). Eight known compounds [ilimaquinone (2.1), renierone (2.7), N-formyl-1,2-dihydrorenierone (2.8), 1,6-dimethyl-7-methoxy-5,8-dihydroisoquinoline-5,8-dione (2.9), mimosamycin (2.10) 7Z-allylidene-5-hydroxy-7,7a-dihydro-2H-cyclopenta[b]pyran-6-one (2.11), flaccidoxide (2.18) and 11S,12S-epoxycembra-1Z,3E,7E-trien-14S-ol (2.19)] and a new diterpene [13S,14R-diacetoxy-11S,12R-epoxycembra-1Z,3E,7E-triene (2.20)] were isolated and identified using standard spectroscopic techniques. Anomalies in the published spectral data of 2.1 and 2.8 were exposed and corrected, and the absolute stereochemistry of the cembrane diterpenes 2.18 and 2.20 established using the modified Mosher’s method. The comparative activities of the nine natural products against four cancer cell lines (A549, LOX, OVCAR3, SNB19) are reported. The second part of the thesis (Chapter Three – Chapter Six) is concerned with an ecological, structural and synthetic study of diterpenes from the endemic South African pulmonate limpet Trimusculus costatus. Two new labdane diterpenes [6b,7a-diacetoxylabda-8,13E-dien-15-ol (3.10) and 2a,6b,7a-triacetoxylabda-8,13E-dien-15-ol (3.11)] were isolated from T. costatus and evaluated for anti-feeding activity against the common predatory fish Pomadasys commersonnii. A strategy for the semi-synthesis of 3.10 from rhinocerotinoic acid (4.14), a diterpene reportedly present in the ubiquitous South African shrub Elytropappus rhinocerotis, was devised in order to allow further bioactivity tests to be performed and unequivocally assign the unknown absolute stereochemistry of the T. costatus metabolites. Attempts to isolate rhinocerotinoic acid from local specimens of Elytropappus rhinocerotis were unsuccessful, and as the repetition of a published synthesis of 4.14 from (-)-sclareol (4.15) gave rhinocerotinoic acid in unacceptably low yields with poor stereoselectivity, an improved synthesis of 4.14 is presented. Comprehensive studies using hispanone (5.1) as a model compound showed that 6,7-dioxygenated labda-8-enes could be prepared from compounds possessing a 7-oxo-labda-8-ene skeleton with some degree of stereocontrol. In the process, fourteen new hispanone analogues were prepared and most of these were tested for activity in a suite of ten agro-chemical assays. The novel compound 7b-hydroxy-9a-carbonitrile-15,16-epoxylabda-13(16),14-dien-6-one (5.34) exhibited significant activity against the crop fungus Phytophthora infestans and is currently being subjected to further agro-chemical tests. Unfortunately, the results from the oxygenation study performed on the model compound 5.1 could not be directly extrapolated to rhinocerotinoic acid. Attempts to prepare the naturally occurring 3.10 from 4.14 via an alternative route were unsuccessful but yielded an analogue of 3.10 in which the substituents at C-6 and C-7 are in a diequatorial rather than a diaxial configuration.

Page generated in 0.0518 seconds