Univ., Diss.--Göteborg, 2006. / Enth. außerdem 5 Zeitschriftenaufsätze.

Thesis (Ph.D.)--Tufts University, 1975. / Submitted to the Dept. of Chemistry. Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

The coenzyme B12-dependent enzyme glutamate mutase (E.C. 5.4.99.1) catalyses the rearrangement of (2S)-glutamic acid to (2S,3S)-3-methylaspartic acid. Each of the two components of the enzyme was purified to homogeneity using a combination of low and high performance chromatographic techniques. Component E and S displayed molecular weights of 53 KDa and 13 KDa respectively as determined by gel electrophoresis, contrary to literature reports. A large number of glutamate and 3-methylaspartate analogues were synthesised and tested as substrates for the enzyme from Clostridium tetanomorphum. No rearrangement products could be detected for (2S,3R)-3-methylaspartic acid, (2S,3S)-3-ethylaspartic acid, 3-methylglutamic acid, (2S,3R)-3-methylsuccinic acid or A/-methyl-3-methylaspartic acid. Five inhibitors were discovered for the enzyme. Four of them were typical competitive inhibitors: (2S,3S)- and (2S,3R)-3-methylglutamates (Ki = 1.0 mM and Ki = 1.5 mM respectively); (2S)-homocysteic acid, Ki = 5 mM; and 1-bromo-cis-1,2-cyclopropanedicarboxylic acid (Ki= 2.2+/-0.2 mM). Finally 1-bromo-trans-1,2- cyclopropanedicarboxylic acid prevented the enzyme from processing (2S)- glutamic acid for periods of times proportional to its concentration. Our results support a radical mechanism with a protein bound glycyl radical as an intermediate, and provide evidence for the existence of two distinct conformations of the holoenzyme, prior to and after the activation of the cofactor. (2S,3R)-3- and (2S,3S)-3-Methylglutamic acids were synthesised stereospecifically by extending Schollkopf's bis-lactim ether methodology. The attack of various carbon anions at C-5 of isopropyl N-benzyl-(4S,5R)-1,2,3- oxathiazolidone-5-methyi-4-carboxyiate S,S-dioxide was not a versatile pathway. Nevertheless, the reaction of the oxathiazolidone with an allylmagnesium lithium cuprate complex gave some promising results, but more research is necessary to optimise certain problematic steps. Several different routes were evaluated for the preparation of 1-amino-1,2-cyciopropanedicarboxylic acid, but either low yields or instability of intermediates thwarted any attempts to achieve this goal. Finally 1- bromo-cis-and trans-1,2-cyclopropanedicarboxylic acids were synthesised by reacting methyl acrylate with methyl dibromoacetate in the presence of sodium hydride. The two pairs of enantiomers, cis- ((2S,3S) and (2R,3R)) and trans- ((2R,3S) and (2S,3R)) were separated by selective ester formation.

Preliminary studies have been undertaken on the enzyme, glutamate mutase. Stereochemically pure (2S,3S)-3-ethylaspartic acid has been synthesized. The turnover of this substrate analogue by glutamate mutase has been investigated. Possible reaction products have been synthesized. (2S,3S)-[1',1',2',2',2'-2H]-3-Ethylaspartic acid has been prepared and a novel synthesis of [1-2H]-ethanol has been investigated with the aim of preparing (2S,3S)-[1'-2H]-3-ethylaspartic acid. In order to investigate the mechanism of elimination of ammonia from (2S,3R)-3-methylaspartic acid, by the enzyme 3-methylaspartase, stereospecific routes to (2S,3R)-3-methylaspartic acid and [3-2H]-(2S,3R)-3-methylaspartic acid have been explored. The compounds were obtained in high enantiomeric excess and with >97 % incorporation of deuterium into the latter. It has been demonstrated that 3-methylaspartase catalyses the direct elimination of ammonia from these substrates, presumably by a syn- elimination mechanism. The kinetic parameters, Vmax and Km, have been determined for both compounds at 1 and 50 mM potassium ion concentrations. A deuterium isotope effect on (D(V)) of 7.15 +/- 2.74 was measured for the reaction at 1 mM potassium ion concentration. A large D(V) of 6.79 + 0.92 was also observed at 50 mM potassium ion concentration, in contrast to results with the natural isomer which show the effect is completely suppressed at this potassium ion concentration. Values for D(V/K) were also obtained at 1 and 50 mM potassium ion concentrations. They were 3.39 +/- 1.6 and 4.10 +/- 1.3, respectively. The 15N isotope effect on V/K was measured at 1 mM potassium ion concentration. A value of 1.0028 +/- 0.0040 was observed for (2S,3R)-3-methylaspartic acid, and, a value of 1.0033 +/- 0.0043 observed for [3-2H]-(2S,3R)-3-methylaspartic acid.

The amino acid sequence determination of Phascolopsis gouldii hemerythrin in the region of the proposed iron ligand at position 58 was the main objective of this research endeavor. Generation of a large peptide was pursued by trypsin digestion of citraconylated hemerythrin producing peptide 50-113 for sequenator analysis. Detection of the phenylthiohydantoin amino acid derivatives by gas-liquid and high-performance-liquid chromatography yielded unambiguous sequence elucidation through the region of interest identifying residue 58 as glutamic acid.

Thesis (PhD)--Stellenbosch University , 1990. / ENGLISH ABSTRACT: Monatin, or 4-hydroxy-4-(3-indolylmethyl) glutamic acid is a high-intensity sweet tasting amino acid found in the root bark of the indigenous plant Schlerochiton ilicifolius. In the thesis the isolation, structure elucidation and a number of synthetic approaches toward the total synthesis of monatin are described. Extensive fractionation of an aqueous extract of the root bark of S. ilicifolius using AG50WX8 strong acid cation exchange resin followed by successive gel filtration procedures using Biogel P2- and Sephadex G10 gels and guided by the intense sweet taste resulted in the isolation of monatin as a mixture of salts in which the sodium salt predominates. Potassium and calcium are the two other cations present. The structure elucidation is based mainly on the analysis of data obtained for monatin and the lactone ester of the N-2,4-dinitrophenyl derivative, prepared by reaction of monatin with Sangers reagent and diazomethane, by 1H and 13C n.m.r. techniques. The X-ray crystallographic study of both monatin and the derivative proved disappointing in that the reflections measured were weak and as a consequence refinement of the data was severely curtailed. However the resultant structures do show the skeletal atoms of the two compounds and in each case the relative stereochemistry of the two chiral centres could be deduced. A comparison of the specific rotation of monatin with those of related 4-hydroxy-4-methylglutamic acids indicates that monatin could have the (2S,4S) configuration. Retrosynthetic analysis of the monatin molecule identified a number of routes which could be utilized for the synthesis of monatin and analogues in which the indole moiety is replaced by a phenyl or aryl group. Seven approaches toward the synthesis of monatin were investigated using in most instances model compounds to establish optimum reaction conditions. Only the last approach, based on a 1,3-dipolar cyclo-addition reaction met with a measure of success: reaction of the 1,3-dipolar compound formed by reaction of N-t-Boc-indole-3-aldehyde with methyl N-benzylglycinate, with the dipolarophile methyl 2-acetoxyacrylate, generated a pyrrolidine with the requisite substituents needed for the monatin structure. In the event the final step, the cleavage of the C-2--N bond of the substituted pyrrolidine ring to give monatin, failed. During the investigation of the 1,3-dipolar cycloaddition reaction several substituted pyrrolidines were prepared. In each case several racemic stereoisomers were formed. In addition a number of substituted oxazolines and pyrrolizidines were obtained as minor by-products during these reactions. The stereochemistry of these compounds was deduced from the proton-proton nuclear Overhauser effect studies and X-ray crystallographic data. / AFRIKAANSE OPSOMMING: Monatien, of 4-hidroksi-4-(3-indolielmetiel) glutamicnsuur is 'n aminosuur met 'n hoëintensiteit soet smaak, wat in die wortelbas van die inheemse plant Schlerochiton ilicifolius voorkom. In die proefskrif word die isolasie, struktuuropklaring en 'n aantal sintetiese benaderings tot die totaalsintese daarvan beskryf. Omvattende fraksionering van 'n waterige ekstrak van die wortelbas van S. ilicifolius met behulp van AG50WX8 sterksuur-katioonuitruilhars gevolg deur opeenvolgende gelfiltrasies op Biogel P2 en Sephadex G10 filtrasiegel met die intense soet smaak as indikator, het gelei tot die isolasie van monatien as 'n mengsel van soute waarin die natriumsout oorheers het. Kalium en kalsium is die ander twee katione wat ook voorgekom het. Die struktuuropklaring is hoofsaaklik gebaseer op 1H en 13C k.m.r.-data wat vir monatien en die laktoonester van die N-2,4-dinitrofeniel derivaat verkry is. Laasgenoemde verbinding is berei deur reaksie van monatien met Sanger se reagens en diasometaan. Die X-straalkristallografiese studie van beide monatien en die derivaat het teleurstellende resultate gelewer aangesien swak refleksie-intensiteite die daaruitspruitende verfyning beperk het. Die verkreë strukture toon egter weI die raamwerkatome van beide verbindings waaruit die relatiewe stereochemie van die twee chirale sentra afgelei kon word. Vergelyking van die spesifieke rotasie van monatien met die van die verwante 4-hidroksi-4-metielglutamiensure dui daarop dat monatien die (2S,4S) konfigurasie mag besit. Retrosintetiese analises van monatien het 'n aantal sintetiese roetes aangedui wat gevolg kon word vir die sintese van monatien en/of monatienanaloë waarin die indoolbrokstuk denr 'n feniel of arielgroep vervang is. Sewe benaderings waarin modelverbindings gebruik is om die gunstigste reaksietoestande te bepaal, is ondersoek. Slegs die laaste benadering, gebaseer op 'n 1,3-dipolêre siklo-addisiereaksie was gedeeltelik suksesvol, naamlik reaksie van die 1,3-dipolêre verbinding gevorm uit N-t-Boc-indool-3-aldehied en metiel N-bensielglisinaat met 'n dipolarofiel, metiel-2-asetoksi-akrilaat, wat 'n pirrolidien gelewer het met die vereiste substituente benodig vir die monatienstruktuur. Die laaste stap, naamlik splyting van die C-2--N binding van die gesubstitueerde pirrolidienring was onsuksesvol. Die ondersoek van die 1,3-dipolêre siklo-addisiereaksie het verskeie gesubstitueerde pirrolidiene as rasemiese sterioisomere gelewer. Hiermee saam het 'n aantal oksasoliene en pirrolisidiene as byprodukte gevorm en hulle strukture is met behulp van proton/proton kern-Overhauser-effekstudies en X-straalkristallografis afgelei.

No description available.

Abstract not available

A model of acute glutamate- and domoate-induced toxicity was developed and characterized in cultured rat cerebellar granule cells (CGCs) using experimental conditions which preserve the voltage-dependency of NMDA receptor function. Glutamate, which is normally non-toxic to CGCs in physiologic media (pH 7.4), was shown to induce a cytotoxic response after 2 hours when the exposure temperature was reduced from 37�� to 22��. Pharmacological characterization of this response demonstrated that cytotoxicity is mediated by the activation of NMDA receptors, while non-NMDA receptors produce a depolarizing stimulus that enhances release of the voltage-dependent Mg����� blockade of NMDA receptor ion channels. Reduced temperature was shown to facilitate NMDA receptor activation by compromising the ability of CGCs to maintain normal electrochemical gradients during glutamate-induced ion flux. When compared to glutamate, the non-NMDA receptor agonist, domoate, demonstrated an acute cytotoxic response in CGCs that was also mediated predominantly by NMDA receptors. NMDA receptor activation was produced secondary to a domoateinduced release of glutamate and aspartate from CGCs; therefore, domoate synergistically potentiates glutamate/aspartate-mediated neurotoxicity. Domoate-induced excitatory amino acid (EAA) release was investigated and found to occur almost exclusively through reversal of the high affinity Na+-coupled glutamate transporter and by osmoregulatory mechanisms. CGCs also responded to domoate-induced depolarization by releasing adenosine which suppresses exocytotic EAA release through A1 receptor activation. The functional and pharmacological characteristics of NMDA receptors were characterized in 12 DIC CGCs using the channel blocking compound [��H]MK-801 (dizocilpine). Kinetic analysis of [��H]MK-801 binding indicated the possible existence of at least two NMDA receptor populations on 12 DIC CGC membranes, and the equilibrium competition binding of MK-801 and other channel blocking compounds was consistent with the presence of high and low affinity binding sites. The neuroprotective potencies of NMDA receptor channel blockers correlated significantly with their affinities for the NMDA receptor derived from equilibrium competition analysis of [��H]MK-801 high-affinity binding. Thus, whereas 12 DIC CGCs express a pharmacologically heterogeneous population of NMDA receptors, it is the high-affinity component of [��H]MK-801 binding that mediates glutamate toxicity. / Graduation date: 1998