Escherichia coli phosphoenolpyruvate carboxykinase (ATP:oxaloacetate carboxylase (transphorsphorylating) EC 4.1.1.49) catalyzes the decarboxylation and subsequent phosphorylation of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) in the presence of Mg2+ATP and synergistic catalysis has been observed in the presence of Ca2+ or Mn2+. Structural analyses have shown that active site residues Arg333, Ser250 and Tyr207 are coordinated differently in E. coli PCK structures complexed with Mg2+ATP-oxalate, Mg2+ATP-Mn2+-pyruvate and Mg2+ATP-Ca2+-pyruvate; hence, we hypothesize that the function of Arg333, Ser250 and Tyr207, depends on the absence or presence of Ca2+ or Mn2+ during catalysis by E. coli phosphoenolpyruvate carboxykinase (PCK). In order to verify this hypothesis, site directed mutagenesis of the pckA gene was used to convert Arg333 to Gln, Ser250 to Ala and Tyr207 to Phe, while 14CO2 exchange assay and x-ray crystallography were used to determine the effects of these mutations on catalysis by E. coli PCK in the presence of OAA and Mg2+ATP with Ca2+ or Mn2+ metal ions. Kinetic analysis showed that the Tyr207Phe mutation decrease kcat by 1.7 fold, while Ser250Ala and Arg333Gln reduced kcat by 10.8 and 4,555 fold respectively in the presence of Mg2+ATP and OAA. In the presence of Mg2+ATP, OAA and Ca2+, Arg333Gln, Ser250Ala and Tyr207Phe mutations reduced kcat by 11,688, 44 and 2 fold respectively. In the presence of Mg2+ATP, OAA and Mn2+ Arg333Gln, Ser250Ala and Tyr207Phe mutations reduced kcat by 2,880, 4 and 5.5 fold respectively. The crystal structure of Ser250Ala complexed with Mg2+ATP-Mn2+-pyruvate, showed that in the presence of Mn2+, Ser250Ala mutation reduced the angle between the γ-phosphate of ATP and residue 250 by 6.2 Å and increased the distance between the hydroxyl group of Tyr207 and the CH2 group of pyruvate by 0.5 Å. As a result we conclude that Arg333 is important for oxaloacetate decarboxylation and phosphorylation. During catalysis in the presence of Mg2+ATP with or without Ca2+ or Mn2+, Ser250 functions to maintain one γ-phosphate oxygen of ATP in an eclipsed conformation, while Tyr207 functions to drive oxaloacetate decarboxylation during catalysis in the presence of Mn2+ ion. Kinetic and structural studies of E. coli PCK have previously been used to show that Asp269 is involved in metal coordination, while Lys254 and Arg65 are important for Mg2+ATP and OAA binding to E. coli PCK respectively. In this study the E. coli PCK Asp269Asn-Mg2+ATP-Ca2+-pyruvate crystal structure showed that the Asp269Asn mutation reduced the number of ligands coordinating Ca2+ from seven to three, while no electron density was observed for Mg2+ATP and OAA in Lys254Ser and Arg65Gln crystal structures respectively.

This thesis describes the preparation and study of a wide range of supported gold catalysts based on atomically-precise triphenyl phosphine stabilised gold clusters. This selected range of ligand-stabilised gold clusters were prepared in attempt to study the effect of increasing cluster nuclearity on the electronic and catalytic properties of these materials. A novel far-infrared study was conducted on the pure cluster materials in attempt to understand the metal-metal and the metal–ligand vibrations, which was also compared to the simulated spectra for each cluster. The design and activation of these novel catalysts based on gold clusters was discussed and the factors that influence activity were described. A comprehensive photoelectron study of the catalysts was conducted in an attempt to understand the electronic structure of the supported gold clusters and the effect of various activation conditions have on the electronic structure of the gold clusters. A selection of the prepared supported gold catalysts were tested for their catalytic activity for the partial oxidation of styrene and the influence of the several activation conditions on the reactivity of the catalyst is also examined. In collaboration, the application of a selection of ligand-stabilised gold clusters as hydrogen sensors and as catalysts for the photocatalytic generation of hydrogen from ethanol is also investigated.

The iridoids are a large family of monoterpenoid natural products that possess a wide range of biological activities. A great deal of research has already been done in the field of iridoid total synthesis, but limitations still remain. Specifically, few syntheses of iridoid β-glycosides have been reported. This work describes the 14 step asymmetric total synthesis of the iridoid β-glycoside (+)-geniposide utilizing a phosphine-catalyzed [3+2] cycloaddition as the key step. Other noteworthy steps in the synthesis include a palladium-catalyzed kinetic resolution and a previously unutilized method for iridoid glycosidation. In addition to describing the synthesis of (+)-geniposide, this dissertation will also review 1) phosphine-catalyzed cycloaddition reactions and 2) previous enantioselective total syntheses of iridoid glycosides. / text

[Rh(CO]2Cl]2 has been shown to catalyze sequential, mechanistically- distinct transformations in one pot. Tandem allylic alkylation/cycloisomerization sequences have been developed to access valuable, complex structures from relatively simple substrates. A methodology for the enantioselective conjugate addition of 2-heteroaryl nucleophiles to a variety of Michael acceptors has been developed. This method was used successfully in an ongoing approach to the synthesis of cortistatin A. 10 linear steps have been completed towards the synthesis of cortistatin A, including a highly regioselective propargylation to install a quaternary carbon and a diastereoselective intramolecular Diels-Alder reaction. / text

The aim of the work carried out in this thesis is to develop new efficient catalytic systems for the synthesis of enantioenriched secondary alcohols. The access to this class of important synthetic intermediates is possible either by nucleophilic addition of organometallic reagents to aldehydes or by reduction of prochiral ketones catalysed with chiral complexes. We have thus developed two new catalytic systems for the asymmetric hydrosilylation of ketones using polymethylhydrosiloxane (PMHS) as an inexpensive reducing agent. A first approach is based on the synthesis of new N, S ligands and zinc complexes bearing a ferrocenyl backbone with planar chirality. Those compounds were prepared and evaluated first in the addition of diethyl zinc to aldehydes, reaching enantiomeric excesses up to 74%. The precatalysts were also evaluated in the reduction of prochiral ketones with PMHS. In that case, a good reactivity was observed and enantioselectivities up to 61% could be reached. It is assumed that a zinc hydride complex formed by thermal ß-elimination of the corresponding ethyl complex is the active species. This catalytic system also allows the hydrosilylation of dialkyl ketones, a challenging goal in asymmetric catalysis. In a second part of this work, we have developed a new catalytic system for hydrosilylation of ketones based on the hypothetical formation of a chiral cobalt hydride catalyst. This intermediate is supposed to be formed by reaction of the corresponding neutral cobalt (II) complex with tetrabutyl ammonium triphenyldifluorosilicate (TBAT) as activator and a silane. Following a preliminary screening, salen type ligands were found to be the most efficient when activated with TBAT in presence of PMHS. Modifications on this structure by replacing the phenol group of the ligand by various sulfonamide groups led, after optimisation of the reaction parameters, to a highly efficient catalytic system with enantioselectivities reaching 84 % for the reduction of tetralone. This work should thus open new perspective for the design of highly enantioselective and low cost catalytic systems for the hydrosilylation of prochiral ketones.

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