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1
Wildervanck, Alexander Franciscus. "Separation of enantiomers of Baclofen". Master's thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/20462.
Testo completoAbstract (sommario):
(3-(Aminomethyl)-4-chlorobenzenepropanoic acid (Baclofen), 3-(p-chlorophenyl)pyrrolidone (Baclofen lactam) and 3-(p-Chlorophenyl)glutaramide (baclofen's synthetic precursor) were individually used as substrates in co-crystallisation experiments with several resolving agents. Experiments were conducted in the solid state and in solution. The (-) enantiomer of the lactam and the ( +) enantiomer of the glutaramide were found to cocrystallise selectively with (2R,3R)-( +)-tartaric acid and (S)-(-)-a.-Methylbenzylamine respectively. Both these dissociable diastereomers Vere analysed by X-ray crystallography. HPLC analysis of the lactam retrieved from the former co-crystals indicated only partial separation of its (+) and (-) enantiomers. X-ray crystallographic, thermal, and polarimetric analyses were perfom1ed on the ( + )- and (-)-salts of the latter co-crystals. The solubilities of these salts in methanol were found to differ by a factor of 4. A solubility diagram was established showing the phase equilibria of various ratios of these two salts in methanol. The(+) enantiomer of the glutaramide was separated from the methylbenzylamine in the (+) salt by treatment with HCI. This enantiomer was converted to (R)-(-)-Baclofen by means of a Hofinann Rearrangement with an overall yield of 40%. The enantiomeric excess of (R)-(".")-Baclofen was 99.7%.
2
Barros, Georgia de Oliveira Figueiredo. "Resolução de misturas racemicas por acoplamento de cristalização a cromatografia em leito movel simulado : estudos fundamentais para a produção de S-cetamina". [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267314.
Testo completoAbstract (sommario):
Orientador: Everson Alves MirandaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-04T07:13:28Z (GMT). No. of bitstreams: 1 Barros_GeorgiadeOliveiraFigueiredo_M.pdf: 2282903 bytes, checksum: b104323f697a813ec6af57b15ba7b95b (MD5) Previous issue date: 2005
Resumo: A separação de enantiômetros em altos níveis de pureza enantiomérica é atualmente um requerimento da industria farmacêutica. No entanto, altas purezas estão sendo alcançadas neste sistema com comprometimento da produtividade. O acoplamento do leito móvel simulado (LSM) a uma etapa de cristalização pode resultar num processo de maior produtividade global . A escolha do método de cristalização para a resolução de misturas racêmicas por cristalização é dependente do tipo de cristal (conglomerado ou composto racêmico) e da localização do ponto eutético no diagrama de solubilidade. O ponto eutético difine a mínima puraza enantiomérica que deve ser fornecida pelo LMS para assegurar que a cristalização irá produzir somente um dos enantiômeros puros. A cetamina é um anstésico que possui um isômero R com indesejáveis efeitos colaterais. O objetivo deste trabalho é trabalho é o desenvolvimento de conhecimento básico (identificação do tipo de racemato e seu ponto eutético no diagrama de solubilidade) para o acolplamento do LMS a uma etapa de cristalização a fim de produzir o isômero S da cetamina em pureza enantiomérica e produtividade alta. Para caracterizar a natureza cristalina da cetamina, diração de raios-X e espectroscopia de infravermelho da mistura racêmica e dos enantilômero puros foram realizados e as curvas de solubilidade em função da temperatura foram determinadas...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital
Abstract: The resolution of enantiomers to high levels of enantiomeric purity is presntly a requeriment in the pharmaceutical industry. However, high, purities are reached with this system at the expenses of productivity. Coupling of simulated moving bed (SMB) to a crystallization step can result in a process whith a overall higher productivity. The choise ofcristallization method for the resolution of racemic mixtures is dependent on the eutetic point on the solubility diagram. Eutetic point is the minimum enantiomeric purity that has to be delivered by the SMB to assure that crystallization will produce just one pure isomer. Ketamine is a anesthetic that has a R-isomer with undesirable side-effect. The objective of this work was development of basic knowlwdge for a process (identification of the type of racemate and its eutetic point in the solubility diagram) coupling the SMB to a crystallization step in order to produce the S-isomer of ketamine at high enantiomeric purity and productivity. To characterize the crystalline nature of ketamine, X-ray diffraction and infrared spectroscopy of the racemic mixture and pure enantiomers were performed between powder x-ray pattems, infrared spectra, and solubility curve slopes of the pure enantiomers and racemic mixture indicated racemic compound formation...Note: The complete abstract is available with the full electronic digital thesis or dissertations
Mestrado
Desenvolvimento de Processos Biotecnologicos
Mestre em Engenharia Química
3
Bromley, Graham. "Approaches to single enantiomers of cyclopropanes". Thesis, Cardiff Metropolitan University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409442.
Testo completo
4
Anandamanoharan, P. "Isolation of enantiomers via diastereomer crystallisation". Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/19315/.
Testo completoAbstract (sommario):
Enantiomer separation remains an important technique for obtaining optically active materials. Even though the enantiomers have identical physical properties, the difference in their biological activities make it important to separate them, in order to use single enantiomer products in the pharmaceutical and fine chemical industries. In this project, the separations of three pairs of diastereomer salts (Fig1) by crystallisation are studied, as examples of the ‘classical’ resolution of enantiomers via conversion to diastereomers. The lattice energies of these diastereomer compounds are calculated computationally (based on realistic potentials for the dominant electrostatic interactions and ab initio conformational energies). Then the experimental data are compared with the theoretical data to study the efficiency of the resolving agent. All three fractional crystallisations occurred relatively slowly, and appeared to be thermodynamically controlled. Separabilities by crystallisation have been compared with measured phase equilibrium data for the three systems studied. All crystallisations appear to be consistent with ternary phase diagrams. In the case of R = CH3, where the salt-solvent ternaries exhibited eutonic behaviour, the direction of isomeric enrichment changed abruptly on passing through the eutonic composition. In another example, R = OH, the ternaries indicated near-ideal solubility behaviour of the salt mixtures, and the separation by crystallisation again corresponded. Further, new polymorphic structures and generally better structure predictions have been obtained through out this study. In the case of R = CH3, an improved structure of the p-salt has been determined. In the case of R = C2H5, new polymorphic forms of the n-salts, II and III, have been both discovered and predicted. This work also demonstrates that chemically related organic molecules can exhibit different patterns of the relative energies of the theoretical low energy crystal structures, along with differences in the experimental polymorphic behaviour. This joint experimental and computational investigation provides a stringent test of the reliability of lattice modelling to explain the origins of chiral resolution via diastereomer formation. All the experimental and computational works investigated in this thesis are published (see APPENDIX 1).
5
Zheng, Hui. "Stereoselective pharmacokinetics and metabolism of XK469, a new quinoxaline topoisomerase II beta poison, in the rat". Columbus, Ohio : Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1080257372.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxi, 190 p.; also includes graphics. Includes abstract and vita. Advisor: Kenneth K. Chan, Dept. of Pharmacy. Includes bibliographical references (p. 182-190).
6
Kröner, Dominik. "Theory of selective preparation of enantiomers by laser pulses Theorie zur selektiven Präparation von Enantiomeren durch Laserpulse /". [S.l. : s.n.], 2003. http://www.diss.fu-berlin.de/2003/141/index.html.
Testo completo
7
Koza, Gani. "Synthesis of single enantiomers of ketomycolic acids". Thesis, Bangor University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488849.
Testo completo
8
Toschi, Gianna. "Synthetic approaches to single enantiomers of mycolic acids". Thesis, Bangor University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429853.
Testo completo
9
Brookes, Michael H. "The synthesis of the enantiomers of lipoic acid". Thesis, University of Warwick, 1985. http://wrap.warwick.ac.uk/55428/.
Testo completoAbstract (sommario):
Lipoic acid is a biologically important molecule. Whilst the racemate has been available by a number of syntheses for many years, no convenient preparation of the pure enantiomers has so far been described. All the evidence so far presented indicates that only the dextrorotatory isomer is active in vivo, the absolute configuration of which has not been established with certainty. To further elucidate the biochemical role(s) and biosynthesis of this compound, a convenient EPC synthesis would be beneficial. This thesis describes the development of a route to the (R)- and (S)- forms of the target molecule from a member of the "chiral pool". *******
10
McBride, John Joseph. "Development of biosensors for the determination of enantiomers". Thesis, University of Brighton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359142.
Testo completo
11
Thome, Brian Matthew. "Increasing the scale of electrophoretic true moving bed enantiomer separations using voltage gradients and filtration enhancement". Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/b_thome_110706.pdf.
Testo completo
12
Nhujak, Thumnoon. "Quantitative aspects of capillary electrophoresis and chiral analysis". Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270036.
Testo completo
13
Elgarhy, Karim. "The separation of the enantiomers of asparagine by crystallization /". Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=100356.
Testo completoAbstract (sommario):
Enantiomers are chiral molecules (i.e. they are mirror-images of each other). They have identical physical properties except for the rotation of polarized light. However their chemical properties are different when reacting with other chiral molecules. The majority of biological processes involve the reaction of two or more chiral molecules. There is therefore a strong interest coming from the pharmaceutical, food and agricultural industry for the separation of enantiomers.Separation methods such as chromatography exist but are generally expensive and limited in scale. Stereosynthesis often has prohibitive development and operating costs.
For 10 to 15% of known enantiomeric systems, a conglomerate is formed upon crystallization (each individual crystal contains only one type of enantiomer).
Crystallization is widely used as an inexpensive separation process which takes advantage of the difference in solubility of the compounds to be separated and yields very high purities in one separation stage. There is no difference in solubility between two enantiomers but in the special case of conglomerates, a difference in crystallization rate can be used as the driving force for the separation of the enantiomers.
In this project, the effects of the important parameters governing the crystallization of asparagine (ASN) were studied in order to develop a separation method based on crystallization. ASN is an amino acid having two enantiomers (L-ASN and D-ASN) and forming a conglomerate. The effects of mixing speed, crystallization temperature, initial supersaturation and seeds (amount, type and time of addition) on the crystallization rates were studied. The crystallization temperature was shown to have a negligible effect over the range studied. Increasing initial supersaturations had a strong accelerating effect on the crystallization. The addition of L-ASN seeds increased the crystallization rate of L-ASN without affecting that of D-ASN. The corresponding statement was true for D-ASN. Larger amounts of seeds and faster mixing increased crystallization rates. Separation methods were developed and 95.8-97.7% pure enantiomers with yields of 73.1% were obtained in a cyclic process. The growth and desupersaturation rates were also modeled.
14
Meeson, Stephen Russell. "The separation of enantiomers by high performance liquid chromatography". Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278414.
Testo completo
15
Rocco, Anna. "Separation of Enantiomers by Means of NanoO-Liquid Chromatography". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2013~D_20130122_144808-59559.
Testo completoAbstract (sommario):
Nano-liquid chromatography (nano-LC) was selected as analytical tool to develop different methods for chiral separations. Nano-LC offers several advantages over conventional LC, e.g., low sample requirement, short analysis time, easy coupling with mass spectrometer, and use of small amount of reagents, with a consequent low environmental pollution. In case of chiral separations, where expensive chiral stationary phases or chiral mobile phase additives (CMPA) have to be employed, nano-LC results very useful since it allows to perform analysis with small amount of this costly material.
Initially, a derivatized β-cyclodextrin, heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin, was employed as CMPA for the chiral separation of some non steroidal anti-inflammatory drugs. The role of different achiral stationary phases in the separative process was investigated. The employed capillary columns were packed in the laboratory, following the slurry-packing procedure. Subsequently, the performance of a reversed phase C18 particulate packed column was compared with that one of a C18 monolithic column, in combination with cyclodextrins (heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin or hydroxypropyl--cyclodextrin) as CMPA. Finally, hydroxypropyl--cyclodextrin was selected as chiral selector to prepare chiral monolithic columns by one-step synthesis. For this aim, the cyclodextrin was activated as the allyl derivative. The composition of the polymeric mixture of the continuous beds was varied... [to full text]Skysčių nano-chromatografija buvo pasirinkta kaip įrankis kurti įvairius chiralinių junginių atskyrimo metodus. Skysčių nano-chromatografija turi eilę privalumų, lyginant su tradiciniais skysčių chromatografijos metodais, pvz.: mažą bandinio poreikį, trumpą analizės trukmę, suderinamumą su masės spektrometrija ir nedideles tirpiklių, reagentų sąnaudas, todėl mažą aplinkos taršą. Chiralinių junginių analizei atlikti, kai reikalingos brangios chiralinės nejudrios fazės ar chiraliniai judrios fazes priedai, skysčių nano-chromatografija yra ypač naudinga, nes leidžia atlikti analizę su minimaliomis šių brangių medžiagų sąnaudomis. Pirmiausia, derivatizuotas β-ciklodekstrinas, heptakis (2,3,6-tri-O-metil) - β-ciklodekstrinas, buvo panaudotas kaip chiralinis nejudrios fazes priedas kai kurių nesteroidinių priešuždegiminių vaistų enantiomerams atskirti. Buvo įštirtas įvairių achiralinių nejudrių fazių vaidmuo atskyrimo procese. Šiuo tikslu naudojant suspensinį birių dalelių pakavimo metodą laboratorijoje buvo paruoštos kapiliarinės kolonėlės. Vėliau, buvo lyginama C18 biriais sorbentais pakrautų atvirkštinių fazių ir monolitinių kapiliarinių kolonėlių skiriamoji geba, chralinias judrios fazes priedais naudojant ciklodekstrinus (heptakis (2,3,6-tri-O-metil)-β-ciklodekstriną arba hidroksipropil-β-ciklodekstriną). Galiausiai, vienpakopės polimerizacijos būdu buvo gautos chiralines kapiliarines kolonėles, chiralniu selektoriumi naudojant hidroksipropil-β-ciklodekstriną. Šiuo tikslu... [toliau žr. visą tekstą]
16
Cooper, Andrew Donovan. "Resolution of enantiomers using cyclodextrins in NMR and HPLC". Thesis, University of Bath, 1991. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292808.
Testo completo
17
Jonas, Gregory David. "On-line detection of optical activity". Thesis, Birkbeck (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286460.
Testo completo
18
Campbell, Lara Allison. "Applications of metalloporphyrin chemistry : development of D₄-symmetric metalloporphyrins for enantioselective epoxidation of olefins and water-soluble metalloporphyrins for protein-protein cross-linking /". Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Testo completo
19
Deniau, Gildas. "Synthesis and evaluation of β-fluoro-γ-aminobutyric acid enantiomers". Thesis, University of St Andrews, 2007. http://hdl.handle.net/10023/362.
Testo completoAbstract (sommario):
The impact of fluorine in medicinal chemistry is reviewed in the first chapter of this work and the fluorine gauche effect, which has not been fully exploited in medicinal chemistry, is also discussed. GABAA and GABAB receptors are then presented and the synthesis of neurosteroid antagonists acting at GABAA receptors is reported. The synthesis of such compounds was motivated to explore the mode of action of neurosteroids at GABA receptors. The observation that the C-F bond has a strong preference to align gauche to the C-N+ bond in protonated β-fluoroamines stimulated the enantioselective synthesis of 3-fluoro-GABA enantiomers. This was achieved from L- and D- phenylalanine in six steps and in an overall yield of 31%. The preferred conformations of 3-fluoro-GABA in solution are then explored by NMR analysis and ab initio calculations. The biological evaluation of 3-fluoro-GABA enantiomers on GABA aminotransferase was then investigated and showed that the (R)-enantiomer undergoes HF elimination ten times more rapidly than the (S)-enantiomer, suggesting a preferred binding conformation of GABA on GABA aminotransferase. This study demonstrates that the C-F bond can be used as a chemical probe to reveal the binding conformation of a bioactive amine and this offers exciting prospects for future research. The synthesis of 3-fluoro-GABA from phenylalanine indicated that amino acids are practical starting materials for the preparation of β-fluoroamines. This methodology is applied to L-lysine to generate (2R)-fluorohexane-1,6-diamine. The formation of a diamine of potential interest for catalysis is also observed in this synthesis.
20
Pinto, José Jorge Baeta Fontinha. "One-pot enzymatic resolution/separation of enantiomers using green solvents". Master's thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/10824.
Testo completoAbstract (sommario):
Dissertação para obtenção do Grau de Mestre em
BiotecnologiaIn the context of “green” chemistry and sustainable processes, the main goal of this work is to develop a process that would circumvent the current complications of racemic sec-alcohol separation, using alternative solvents and selective enzymatic resolution. In this work the ability of enzymes to perform the resolution of sec-alcohols to obtain high added-value enantiomers is advantageously exploited in the production of pure chiral compounds. Candida rugosa lipase is capable of selectively converting one of the enantiomers of menthol into a different chemical compound with substantial different properties. Following this enzymatic catalysis, a separation method is used recurring to alternative solvents properties to separate the enantiomer that does not react obtaining a pure chiral compound. The main goals of this research are to finding both a vinyl ester and an acid anhydride capable of reacting selectively with the racemic menthol through catalyzed reaction using Candida rugosa lipase and test independently the acylating agents at various parameters that influence the conversion and enantioselectivity of the process such as temperature, enzyme concentration, parallel chemical reaction and solvent effect. Through this work we were successful in testing these two different chemical compounds obtaining high values for conversion and enantioselectivity. In the case of propionic anhydride we obtained 51% of conversion, 89% and 74% of enantiomeric excess of substrate and product, respectively, at 310.15 K in [Omim][PF6]. In the case of vinyl decanoate, we obtained 44.4% of conversion, 90.7% of enantiomeric excess of substrate, at 310.15 K in [Hmim][PF6].
21
Matchett, Michael William. "Resolution of enantiomers using cyclodextrins in HPLC, FSCE and NMR". Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307070.
Testo completo
22
Sebogisi, Baganetsi Karabo. "Separation of racemates via host-guest chemistry". Thesis, Cape Peninsula University of Technology, 2012. http://hdl.handle.net/20.500.11838/730.
Testo completoAbstract (sommario):
Thesis submitted in fulfilment of the requirements for the degree
Magister Technologiae: Chemistry
in the Faculty of Applied Science
at the
CAPE PENINSULA UNIVERSITY OF TECHNOLOGY
2012Chirality is very important to the pharmaceutical industry as enantiomers have the same macroproperties except for their optical and pharmacological activity. Industrial research has thus focused to find the most effective resolution technique. However, our aim was to obtain more information regarding the discrimination process. In this project the structures of the hydrates of di-quininium L-malate, (2QUIN+)(L-MA2-)•2H2O and the di-quininium D-malate, (2QUIN+)(D-MA2-)•2H2O have been investigated. (-)-Quinine (QUIN) did not show selectivity between the D and L malic acid and the structure of (2QUIN+)(DL-MA2-)•2H2O was obtained. Effect of solvents was demonstrated in the study and the structure of (QUIN+)(D-MA-)•H2O) was reported. The relationship between C-O bonds of the carboxylate and carboxylic moieties and ÄpKa was explored in salt and co-crystal formation. Kinetics of absorption was conducted for the reaction of (+)-deoxycholic acid (DCA) with n-propylamine and DCA with racemic sec-butylamine. The rate constants of the reactions were determined. Kinetics of desolvation was performed on the powder samples of mixtures of DCA and sec-butylamine and DCA with di-n-butylamine. Non-isothermal methods were used where a series of TG analyses was carried out at different heating rates (2, 4, 10, 32 K min-1). The structures of DCA with n-propylamine and di-n-butylamine were elucidated. The selectivity of DCA was investigated. The host compound was found to be able to successfully resolve racemic sec-butylamine (2-BUAM) and 2-amino-3-methylbutane (MeBUAM). The structures of DCA with enantiomers of these guests are reported in the study. The structures of R-BUAM and S-BUAM were solved in different space groups while R-MeBUAM and S-MeBUAM crystallized in the same space group.
23
Poletti, Sophia C., Annachiara Cavazzana, Cagdas Guducu, Maria Larsson e Thomas Hummel. "Indistinguishable odour enantiomers: Differences between peripheral and central-nervous electrophysiological responses". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-230788.
Testo completoAbstract (sommario):
The ability of humans to discriminate enantiomeric odour pairs is substance –specific. Current literature suggests that psychophysical discrimination of odour enantiomers mainly depends on the peripheral processing at the level of the olfactory sensory neurons (OSN). To study the influence of central processing in discrimination, we investigated differences in the electrophysiological responses to psychophysically indistinguishable (+)- and (−)- rose oxide enantiomers at peripheral and central-nervous levels in humans. We recorded the electro-olfactogram (EOG) from the olfactory epithelium and the EEG-derived olfactory event-related potentials (OERP). Results from a psychophysical three alternative forced choice test indicated indistinguishability of the two odour enantiomers. In a total of 19 young participants EOG could be recorded in 74 and OERP in 95% of subjects. Significantly different EOG amplitudes and latencies were recorded in response to the 2 stimuli. However, no such differences in amplitude or latency emerged for the OERP. In conclusion, although the pair of enantiomer could be discriminated at a peripheral level this did not lead to a central-nervous/cognitive differentiation of the two stimuli.
24
Igwemezie, Linus Nnamdi. "Stereoselective HPLC analysis, pharmacokinetics, tissue distribution and pharmacodynamics of mexiletine enantiomers". Thesis, University of British Columbia, 1989. http://hdl.handle.net/2429/30655.
Testo completoAbstract (sommario):
Mexiletine [(2',6'-dimethylphenoxy)-2-amino propane] is a class 1 antiarrhythmic agent with a similar chemical structure and electrophysiological effects to those of lidocaine. It is a chiral drug which is used clinically in the racemic form (i.e. 50:50 ratio of two enantiomers). This thesis describes the stereoselective HPLC analysis, pharmacokinetics, tissue distribution and pharmacodynamics of mexiletine enantiomers.
The development of a highly sensitive and stereoselective HPLC assay for mexiletine enantiomers, using 2-anthroyl chloride as a derivatization reagent, was attempted. The synthesis and characterization of the acid chloride was successfully carried out. The 2-anthroyl derivatives of the enantiomers were resolved on a Pirkle[formula omitted] ionic (phenyl glycine) chiral column using a mobile phase of ethyl acetate/2-propanol/Hexane (4:6:90). Detection was accomplished by fluorescense (ex = 270 nm, em = 400 nm) with a lower limit of 0.5 ng/ml. However, there was an interfering peak coeluting with S(+)-mexiletine which could not be resolved. This precluded the use of the assay for the proposed pharmacokinetic and pharmacodynamic studies. A previously developed stereoselective HPLC method, with 2-naphthoyl chloride as a derivatization reagent, was subsequently used.
The in vitro protein binding of mexiletine enantiomers was examined with human serum, lipoprotein deficient serum, albumin and α[formula omitted]-acid glycoprotein. The binding of the enantiomers to human serum was moderate (45 to 50%) within the therapeutic range of mexiletine. This binding was due, mainly, to albumin and α[formula omitted]-acid glycoprotein. The free fractions of the enantiomers decreased significantly (P<0.05) as pH was increased from
7.0 to 8.0. Stereoselective binding was apparent at pH 8.0 such that the free fraction of S(+)-mexiletine was significantly (p<0.05) greater than that of the R(-)-enantiomer. However, stereoselective binding was not observed at physiological pH (≈ 7.4). These results indicated that the serum binding of mexiletine enantiomers is pH-dependent. Binding was not concentration-dependent, nor was there any competitive binding interaction between the enantiomers, within the therapeutic range. Scatchard analysis of the binding data obtained with serum and albumin both showed the presence of 2 classes of binding sites. A high affinity, low capacity site and a low affinity, high capacity site. In contrast, α[formula omitted]-acid glycoprotein showed only 1 class of binding sites and this was a high affinity, low capacity site.
Pharmacokinetic and tissue distribution studies in rats following the administration of racemic mexiletine (10 mg/kg) indicated extensive tissue uptake and rapid elimination of the enantiomers. R(-)-Mexiletine showed a 32% greater systemic clearance (161.8 ml/min/kg vs 122.9 ml/min/kg) than the S(+)-enantiomer. The steady state-volume of distribution was also greater for the R(-)-enantiomer (9.0 L/kg vs 7.4 L/kg), while the elimination half-lives of the enantiomers (1.4 and 1.3 h for R(-)- and S(+)-mexiletine, respectively) were not different. Maximum tissue concentrations were observed at 5 min in all the tissues studied (heart, brain, lung, kidney, liver and fat). These concentrations were not significantly different, except for the liver tissue where a 2.4-fold greater concentration of the S(+)-enantiomer was found. High tissue/serum ratios (>20) were observed for each enantiomer in the brain, lungs and kidneys. The brain accumulated 3-fold the heart concentrations of the
enantiomers.
Pharmacodynamic studies on the relative antiarrhythmic effects of racemic mexiletine and its enantiomers were carried out using electrical and ischaemia-induced arrhythmias in rats. Racemic mexiletine and its enantiomers significantly (P<0.05) increased VFT and ERP. However, the differences between the effects of the 3 drugs on these variables were not statistically significant. R,S-, S(+)- and R(-)-mexiletine caused significant bradycardia and PR prolongation in both pentobarbitone anaesthetized and conscious rats. These effects of the drugs were also not significantly different from each other. In the ischaemic conscious rats, the 3 drugs did not significantly reduce the incidence of VT and VF, the number of PVCs nor the "arrhythmia score" when compared to saline (control). Racemic mexiletine and its enantiomers produced comparable CNS toxicity in the conscious rats.Pharmaceutical Sciences, Faculty of
Graduate
25
Mayo, Patrick Rogers. "Disposition and pharmacodynamics of verapamil enantiomers in the presence of inflammation". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0011/NQ59999.pdf.
Testo completo
26
Del, Alamo Aurora. "Studies of hexahelicene bonded phases for the HPLC resolution of enantiomers". Thesis, University of Warwick, 1995. http://wrap.warwick.ac.uk/3994/.
Testo completoAbstract (sommario):
The thesis presents a review of the literature on the HPLC resolution of enantiomers using chiral stationary phases and discusses the mechanisms of separation and the utility of these phases. The synthesis and chemical, chiroptical and spectroscopic properties of helicenes are also reviewed and the potential utility of helicene-based for the HPLC resolution of enantiomers is discussed. The work carried out involved the preparation of a hexahelicene-based chiral stationary phase and demonstrations of its utility for the resolution of chiral analytes. This phase was chemically bonded rather than physically coated, in order to make it stable to hydrolysis and solvent stripping, and therefore to permit its employment with a wide range of mobile phases. This thesis describes the synthesis of hexahelicen-7-ylacetic acid methyl ester, including confirmation of the structure of the key synthetic intermediates by spectroscopic analysis, and the investigation of several proceduresfor the resolution of hexahelicen-7-ylacetic acid methyl ester into its enantiomers, one of which enabled around 100 mg amounts of each of (+) and (-) enantiomers of hexahelicen-7-ylacetic acid to be obtained in highly chemically and optically pure form. The thesis also gives an account of several synthetic approaches to covalently bonding of the chiral selector (hexahelicen-7-ylacetic acid) to a modified silica stationary phase. Chiral stationary phases were prepared from each of the enantiomers in sufficient amount to permit the packing of analytical columns of these phases. Chiral solutes containing nitroaryl functionalities were synthesised to investigate the chiral resolving power of these novel phases. Adequate separations were obtained with both chiral stationary phases and, as anticipated, the eluting order of chiral analytes was reversed between the (+) and (-) stationary phases. The work demonstrated the utility of these columns for the resolution of nitroaryl-containing chiral analytes.
27
James, Bryce. "(+/-)-Z-bisdehydrodoisynolic acid and specific enantiomers : effects on traumatic brain injury /". Available to subscribers only, 2007. http://proquest.umi.com/pqdweb?did=1459903541&sid=1&Fmt=2&clientId=1509&RQT=309&VName=PQD.
Testo completo
28
Vollmer, Heidi R. "Biologically active natural product synthesis". Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365780.
Testo completo
29
Collicott, Roland. "Investigation of chiral silicon compounds for the determination of enantiomeric purity". Thesis, n.p, 2001. http://ethos.bl.uk/.
Testo completo
30
Kim, Sunghee. "Olfactory discrimination ability of South African fur seals (Arctocephalus pusillus) for enantiomers". Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-78364.
Testo completoAbstract (sommario):
The sense of smell in marine mammals is traditionally thought to be poor. However, increasing evidence suggests that pinnipeds may use their sense of smell in a variety of behavioral contexts including communication, foraging, food selection, and reproduction. Using a food-rewarded two-choice instrumental conditioning paradigm, I assessed the ability of South African fur seals, Arctocephalus pusillus, to discriminate between 12 enantiomeric odor pairs, that is, between odorants that are identical in structure except for chirality. The fur seals significantly discriminated between eight out of the twelve odor pairs (according to p < 0.05, with carvone, dihydrocarvone, dihydrocarveol, limonene oxide, menthol, beta-citronellol, fenchone, and alpha-pinene), and failed with only four odor pairs (isopulegol, rose oxide, limonene, and camphor). No significant differences in performance were found between the animals (p > 0.05). Cross-species comparisons between the olfactory performance of the fur seals and that of other species previously tested on the same set of odor pairs lend further support to the notion that the relative size of the olfactory bulbs is not a reliable predictor of olfactory discrimination abilities. The results of the present study suggest that sense of smell may play an important and hitherto underestimated role in regulating the behavior of fur seals.
31
Igwemezie, Linus Nnamdi. "Stereoselective HPLC analysis of mexiletine enantiomers : pharmacokinetics and protein binding in humans". Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/25901.
Testo completoAbstract (sommario):
Mexiletine is a relatively new class IB antiarrhythmic agent, similar in structure and pharmacological effects to lidocaine. It is effective mainly against ventricular arrhythmias and can be administered by the oral route, mexiletine is a chiral drug which is used clinically as the racemic mixture. The enantiomers of numerous chiral drugs have been shown to differ in their disposition in the body due to their stereoselective pharmacodynamic and/or pharmacokinetic properties. The relative antiarrhythmic potencies of the individual enantiomers of mexiletine have not been studied, nor have their pharmacokinetics been properly elucidated. Thus, the present study was aimed at developing a highly sensitive and stereoselective assay for mexiletine enantiomers which will be utilized to study their pharmacokinetics and in vitro serum protein binding.
A high-performance liquid-chromatographic assay was developed using the Pirkle[sup R] ionic chiral stationary phase. The enantiomers were resolved as their 2-naphthoyl derivatives. The HPLC mobile phase consisted of 5.5% 2-propanol in hexane and was delivered at a flow rate of 1.4 mL/min. Detection of the enantiomeric derivatives was accomplished with a fluorescence detector [230 nm (Ex) and 340 nm (Em)]. Recovery of the enantiomers from plasma after
pH adjustment to above 12 was found to be substantially low
and stereoselectively in favour of the S(+)-enantiomer when
compared with their recovery from water. This was attributed
to a greater plasma protein binding of the R(-)-isomer
despite the high plasma pH. Recovery was improved (83%),
and the natural enantiomeric ratio restored by precipitation
of the plasma proteins with barium hydroxide/zinc sulfate.
Linear calibration curves (r² >0.999) were obtained in
plasma over the concentration range 5 to 750 ng/mL for each
enantiomer. Similar correlations (r >0.999) were obtained in saliva from 10 to 1,500 ng/mL and in urine from 0.25 to 7.5 ug/ml and 10 to 500 ng/ml. The inter- and intra-assay coefficients of variation were less than 4% for all the biological fluids. The minimum detectable quantity of each enantiomer in plasma was 5 ng/mL at a signal-to-noise ratio of 5:1, representing 100 pg injected onto the column.
Protein binding of the enantiomers was determined with serum from five healthy male subjects. The mean percent free fraction of R(-)-mexiletine, 19.80 ± 2.64% was significantly (P<0.001) less than that of S(+)-mexiletine, 28.32 ± 1.45%. Binding was independent of concentration over the therapeutic range.
Five healthy male subjects (same as above) were given 300 mg of (±) -mexi letine hydrochloride (capsules) orally. The plasma concentration-time data were analyzed by AUTOAN and NONLIN computer programs. The enantiomer kinetics were best described by a triexponential function in three of the five subjects and a biexponential function in the remaining two. There was no statistically significant difference in the absorption and distribution rate constants, peak plasma concentrations, time to peak plasma concentrations and plasma AUCs of the enantiomers. Bioavailability of the enantiomers was not determined due to lack of approval from the Health Protection Branch (Canada) to administer intravenous (±) -mexiletine to healthy volunteers. The terminal elimination half-life from plasma data for R (-)-mexiletine, 9.1 ± 2.9 hours, was significantly (P<0.02) less than that for the S( + )-isomer, 11.0 ± 3.8 hours. The cumulative urinary excretion of S(+)-mexiletine was 9.14 ± 3.07%, which was significantly (P<0.01) greater than that of R(-)-mexiletine, 7.40 ± 2.40%. Renal clearance of the enantiomers was consistent with cumulative urinary excretion, 0.72 ± 0.26 mL., min-1.Kg-1 and
0.61 ± 0.20 mL.min⁻¹.Kg⁻¹respectively (P<0.05).
The non-renal elimination rate constant (mainly metabolism)
was significantly (P<0.001) greater for R(-)-mexiletine, 0.0763 ± 0.0273 h⁻¹, than for the S( + )-iosmer, 0.0634 ± 0.0270 h⁻¹. The saliva AUCS were 18.2. ± 6.3 ug.mL ⁻¹.hr and 14.1 ± 5.0 ug. mL⁻¹.hr for
S(+)-mexiletine and the R(-)-isomer respectively (difference significant, P<0.01). The enantiomer concentration ratios (R/S) in the three biological fluids showed evidence of a cross-over [R(-)> S(+) to S(+)>R(-)] between 0-2 hours in urine and saliva and 8-10 hours in plasma. This indicated an apparent discrepancy in the cross-over time in plasma relative to urine and saliva. However, the free enantiomer concentration ratios in plasma were similar to the enantiomer ratios in urine and saliva.
Thus the disposition of mexiletine enantiomers in man is stereoselective with serum protein binding and metabolism favouring the R(-)-isomer. Renal elimination and salivary secretion, on the other hand, favour the S(+)-isomer. The similarity between the free enantiomer ratios in plasma, urine and saliva suggests that the stereoselective renal elimination and salivary secretion of the enantiomers are a reflection of their stereoselective protein binding.Pharmaceutical Sciences, Faculty of
Graduate
32
Ravichandran, Easwaran. "The fate of racemic chloroquine and its enantiomers in male F344 rats". Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404566.
Testo completo
33
Rimmer, Duncan Adam. "Novel asymmetric microenvironments for separation of enantiomers chiral drugs and natural products". Thesis, Open University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254965.
Testo completo
34
Hutchaleelaha, Athiwat. "Disposition kinetics of the enantiomers of methamphetamine and its metabolites in rats". Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187315.
Testo completoAbstract (sommario):
Methamphetamine (MAP), the N-methyl derivative of amphetamine (AP), has been abused by human populations in several countries. There are stereoisomeric differences in the pharmacodynamics of the enantiomers with the d-enantiomer of both drugs being more potent than the antipode in its central stimulating effects. The stereoisomeric differences in disposition kinetics of MAP and its metabolites were studied in rats. Several sensitive enantiomer-specific HPLC methods were developed to quantitate enantiomers of MAP and its metabolites in serum and urine samples. The optical isomers of these compounds are derivatized by reacting with a chiral fluorescent reagent, (-)-1-(9-fluorenyl)ethyl chloroformate, before separation on a reverse-phase HPLC column. These methods have sensitivities in the low ng/ml range. Both MAP and AP are low protein-bound drugs. There are slight differences in serum protein binding between MAP enantiomers. The binding of d-AP is greater than l-AP. Following administration of racemic MAP to rats, the serum concentration of the d-enantiomer was higher than the l-enantiomer. The metabolites recovered in urine are enantiomers of MAP, AP, p-hydroxymethamphetamine (OHMAP) and p-hydroxyamphetamine (OHAP). A greater amount of the d-enantiomer of MAP and AP could be recovered compared with the l-enantiomer. The hydroxylated metabolites were excreted as unconjugated and conjugated forms with the total l-enantiomer being higher than the antipode. There are stereoisomeric differences for both clearance and volume of distribution of MAP. When racemic AP was administered, AP and unconjugated and conjugated of OHAP could be recovered in urine. Both clearance and volume of distribution of l-AP are significantly higher than d-AP. The clearance of d-OHMAP is greater than that of l-OHMAP. The change in enantiomeric ratio (l-/d-) of metabolites following MAP compared to that following AP suggested the existence of multiple stereoselective pathways involved in the disposition of these compounds. The differences in serum concentrations between AP enantiomers was magnified following racemic MAP, which suggested stereoselective N-demethylation. There are no differences in disposition kinetics of MAP between Sprague-Dawley and Fisher 344 rats. Activated charcoal given orally 10 minute before an iv dose of racemic MAP did not enhance the elimination of the drug in vivo.
35
Fernandes, Andreia Patrícia Macedo. "Separation of mandelic acid enantiomers using aqueous biphasic systems containing chiral selectors". Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/22869.
Testo completoAbstract (sommario):
Mestrado em Bioquímica - Métodos BiomolecularesA quiralidade é a uma propriedade importante na indústria farmacêutica, uma vez que um enantiómero de um fármaco pode exercer o efeito terapêutico desejado enquanto o outro pode ser inerte ou mesmo nefasto. Embora vários fármacos sejam comercializados na sua forma racémica, as entidades regulatórias aconselham o desenvolvimento de fármacos enantiomericamente puros e mais seguros. Neste contexto, a indústria farmacêutica procura formas baratas e eficientes de produzir fármacos enantiomericamente puros, sendo este o objetivo da presente tese. A separação enantiomérica do ácido mandélico (AM), aqui utilizado como um fármaco racémico modelo, será tentada recorrendo a sistemas aquosos bifásicos (SABs) constituídos por seletores quirais de origem natural (proteínas e açúcares). Serão usadas duas abordagens: (i) a introdução de proteínas como seletores quirais em diferentes tipos de SABs; e (ii) o uso de (D)-sacarose simultaneamente como seletor quiral e componente de fase em SABs. Na primeira abordagem, foram utilizados diferentes tipos de SABs (polímero+polímero, polímero+sal, sal+líquido iónico (LI), polímero+LI e polímero+açúcar) e duas proteínas (albumina de soro bovino – BSA – e citocromo C – Cit c). A escolha das proteínas assentou em resultados de molecular docking que indicaram interações distintas entre diferentes proteínas e os enantiómeros do AM. Nestas fases, os sistemas constituídos por PPG400+(D)-Sacarose+BSA (excesso enantiómerico de -5.9± 0.5%) e PPG400+dihidrogeno fosfato de colínio+Cit c (excesso enantiomérico de -9.0 ± 1.2%) revelaram-se os mais eficientes. As proteínas e os constituintes de fase dos SABs afetaram a separação enantiomérica de ácido mandélico. Uma vez que a docagem molecular não considera as interações com os componentes de fase, esta abordagem revelou ser incapaz de prever o desempenho das proteínas como seletores quirais em SABs. Com o objetivo de ultrapassar as limitações de seletividade enantiomérica e melhorar a simplicidade operacional da tecnologia proposta, a (D)-sacarose foi usada simultaneamente como formador de fase e seletor quiral em SABs. Depois de uma otimização cuidada, foi possível obter um excesso enantiomérico máximo de -12.3 ± 0.5% com um SAB constituído por polímero e (D)-sacarose.
Chirality is an important property for the pharmaceutical industry, since one enantiomer of a drug can exert a therapeutic action, while the other may be inert or even nefarious. While several drugs are commercialized as racemates, regulatory bodies strongly encourage the development of safer enantiopure drugs. In this context, pharmaceutical industry seeks for cheap and efficient ways of obtaining enantiopure pharmaceuticals and this is the main objective of this thesis. The enantiomeric separation of mandelic acid (MA), here used as a model racemic drug, using aqueous biphasic systems (ABS) composed of natural chiral selectors (proteins and sugars) will be proposed. Two different approaches were used: (i) the introduction of proteins as chiral selectors in several types of ABS; and (ii) ABS formed by D-Sucrose as both phase former and chiral selector. Within the first approach, different types of systems (polymer+polymer, polymer+salt, polymer+sugar, and ionic liquids (ILs)+salt, ILs+polymer) and of proteins (bovine serum albumin –BSA - and cytochrome C – Cyt C) were used. These two proteins were chosen based on molecular docking results that shown distinctive interactions with the two MA enantiomers among eleven screened proteins. PPG400+(D)-sucrose+BSA system (enantiomeric excess of -5.9 ± 0.5%) and PPG+cholinium dihydrogenphosphate+Cyt C (enantiomeric excess of -9.0 ± 1.2% were the most efficient ABS developed up to this stage. Both the protein and ABS phase formers affected the enantioseparation of MA. Since molecular docking does not encompass the interactions with the ABS phase formers, it was limited at predicting the proteins’ performance as chiral selectors in ABS. In order to surpass the limited enantioselectivity displayed and to improve the operational simplicity of the proposed technology, (D)-sucrose was employed as both chiral selector and phase former in ABS. After a proper optimization, it was possible to achieve a maximum enantiomeric excess of -12.3 ± 0.5% with an ABS composed of polymer and (D)-sucrose.
36
Davis, Rachel Anne. "The metabolism of ifosfamide". Thesis, University of Exeter, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294488.
Testo completo
37
Encarnacion-Gomez, Luis G. "Design and operation of enzymatic reactive crystallization: Applications in chiral purity and kinetically controlled synthesis". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54322.
Testo completoAbstract (sommario):
The work presented in this thesis is aimed to design efficient reactive crystallization operations that could potentially be implemented in the manufacture of enantiomerically pure compounds and β-lactam antibiotics. Multiple aspects of solution thermodynamics, reaction engineering and crystallization from complex solutions are involved and will be discussed in detail through the following chapters.
The first piece of this work utilizes reactive crystallization for the manufacture of enantiomerically pure amino acids. Chemo-enzymatic stereoiversion reactions are used to enrich saturated or supersaturated solutions to favor the selection of a desired enantiomer. L-Methionine and L-Phenylalanine were resolve successfully from racemic mixtures by cyclic stereoinversion. r D-amino acids were oxidized by D-amino acid oxidase (D-AAO) and the resulting ketoacid was subsequently reduced by ammonia borane producing a racemic-mixture After the necessary enantiomeric enrichment was reached, system conditions were changed to induce supersaturation and promote crystal formation. In each case crystals with chemical and enantiomeric purities greater than 99% wt. were recovered. experimental information about reaction and crystallization kinetics was used to developed models. Such models were used to design model-based optimizations in which the productivity of the operation was enhanced by selecting an optimal temperature profile.
The second example is a reactive crystallization towards the manufacture of β-lactam antibiotics. One of the major drawbacks of the utilization of enzymes towards the manufacture of β-lactam antibiotics is the fact that the same enzyme that catalyzes the synthesis of the antibiotic also catalyzes its hydrolysis and thus, its degradation. The reaction scheme is a kinetically controlled synthesis in which the desired product is an intermediate within the network. Hence, the focus of this work is to design an efficient reactive crystallization in which the product is crystallized before it is consumed by hydrolysis. In order to accomplish this goal we have study solution equilibria, reaction kinetics, and crystallization kinetics. Even though crystallization kinetics of ampicillin has been previously reported; the reported models are not applicable to a reactive crystallization scheme for a variety of reasons. In this work, we have developed a robust model that can be applied to multiple crystallization protocols that are consistent with the conditions at which the enzymatic reaction can be performed.
Finally, a reactive-crystallization scheme in which ampicillin was successfully recovered from solution was developed. In this work, crystal seeds were used to promote crystallization of the desired product from the complex media. The results indicated that is possible to perform the reaction and crystallization in parallel, and still recover crystals with high purity. This work is the first example in which ampicillin was produced and recovered with high purity in a single stage. Previous work on reaction crystallization of antibiotics reported ampicillin crystallization; however, this was accompanied by precipitation of by-products which greatly reduces the applicability of the operation as product purification is required after the reaction.
38
Leone, Andrea D. "Enantiomeric composition of Chiral pesticides in soil and air from the U.S. cornbelt region". Youngstown State University / OhioLINK, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=ysu997192215.
Testo completo
39
Li, Xiaoping. "Thermodynamic and kinetic characterization of chiral separations with ß-cyclodextrin stationary phase". Diss., Connect to online resource - MSU authorized users, 2006.
Cerca il testo completo
40
Alcala, Saavedra Monica. "Design of solid state composites for enantiomeric separations /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
Testo completo
41
Eriksson, Tommy. "Pharmacokinetics of the enantionmers of thalidomide". Malmö : Lund : Malmö University Hospital ; Lund University, 1997. http://catalog.hathitrust.org/api/volumes/oclc/68945032.html.
Testo completo
42
Fratpietro, Stephen W. "Structural determinations by analytical analysis of 7-phosphanorbornadiene derivatives and amino acid enantiomers". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ60842.pdf.
Testo completo
43
Kaspereit, Malte [Verfasser]. "Separation of Enantiomers by a Process Combination of Chromatography and Crystallisation / Malte Kaspereit". Aachen : Shaker, 2006. http://d-nb.info/1170530893/34.
Testo completo
44
Tan, Soo Choon. "Bioanalysis of ibuprofen enantiomers : application to pharmacokinetic studies in young and elderly volunteers". Thesis, King's College London (University of London), 1996. https://kclpure.kcl.ac.uk/portal/en/theses/bioanalysis-of-ibuprofen-enantiomers--application-to-pharmacokinetic-studies-in-young-and-elderly-volunteers(53fca9ed-c40d-49d6-afdb-9060fc8f1d15).html.
Testo completo
45
Holo, Luxolo. "Enantioselective, potentiometric membrane electrodes for enantioanalysis of amino acids of clinical and pharmaceutical importance". Diss., Pretoria: [s.n.], 2006. http://upetd.up.ac.za/thesis/available/etd-03082010-172629/.
Testo completo
46
Cheney, Matthew A. "Synthesis, resolution, and diastereoselectivity of the chiral auxiliary trans-2-(9H-flouren-9-yl)cyclohexanol". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2007. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Testo completo
47
McCrossen, Sean David. "The role of mobile phase additives on the retention characteristics of solutes in reversed-phase chromatography". Thesis, Birkbeck (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297212.
Testo completo
48
Yeung, Kai Tai. "Molecular simulations of the enantioseparating mechanism of polysaccharide-based chiral stationary phase and enzymatic acylation of N-benzoyl-L-arginine ethyl ester in binary aquo-organic solvent mixtures". HKBU Institutional Repository, 2007. http://repository.hkbu.edu.hk/etd_ra/819.
Testo completo
49
Shibl, Mohamed F. "Mechanisms of double proton tautomerization & quantum control of tautomerism in enantiomers by light". kostenfrei, 2006. http://www.diss.fu-berlin.de/2006/622/index.html.
Testo completo
50
Li, Song 1957. "Liquid chromatographic separation of enantiomers and structurally-related compounds on b-cyclodextrin stationary phases". Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70269.
Testo completoAbstract (sommario):
The retention behaviour of 16 phenothiazines and structurally-related drugs on a $ beta$-cyclodextrin-bonded phase column was studied with respect to pH, mobile phase composition and column temperature. Both isocratic and gradient-elution separations of these compounds were investigated.The enantiomers of twelve racemic dinitrophenyl amino acid derivatives were separated on a $ beta$-cyclodextrin-bonded phase column. The effects of pH, methanol and triethylammonium acetate (TEAA) buffer concentrations on the retention and resolution were investigated. The chiral recognition mechanism was studied by means of UV-visible, circular dichroism and proton nuclear magnetic resonance spectroscopic methods.
A multiple-interaction type of chiral stationary phase was developed by bonding $ beta$-cyclodextrin to silica gel and modifying the cyclodextrin cavity by flexibly capping its primary hydroxyl or small side. These modified $ beta$ cyclodextrin stationary phases contain a hydrophobic cavity, capable of inclusion complexation; aromatic groups, capable of $ pi$-$ pi$ interaction; and polar hydrogen-bonding sites, capable of forming hydrogen-bonding with the polar functional groups of the solutes. These stationary phases exhibit a high stereoselectivity toward a wide variety of chiral compounds. The preparation and properties of these modified $ beta$-cyclodextrin stationary phases are described. The enantiomeric separation of amino acids and their derivatives, of carboxylic acids, of phenothiazine drugs, and of other chiral compounds are reported. The effects of mobile phase composition on the retention and resolution are discussed.