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Tuning the Stereoselectivity of an Intramolecular Aldol Reaction by Precisely Modifying a Metal-Organic Framework Catalyst
(Wiley-VCH GmbH, 2022-06-15) Cornelio J; Telfer SG
We report the catalysis of an enantioselective, intramolecular aldol reaction accelerated by an organocatalyst embedded in a series of multicomponent metal-organic frameworks. By precisely programming the pore microenvironment around the site of catalysis, we show how important features of an intramolecular aldol reaction can be tuned, such as the substrate consumption, enantioselectivity, and degree of dehydration of the products. This tunability arises from non-covalent interactions between the reaction participants and modulator groups that occupy positions in the framework remote from the catalytic site. Further, the catalytic moiety can be switched form one framework linker to another. Deliberately building up microenvironments that can influence the outcome of reaction processes in this way is not possible in conventional homogenous catalysts but is reminiscent of enzymes.
The synthesis and chemistry of [2.2]paracyclophane amino acid derivatives : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Manawatū, New Zealand
(Massey University, 2020) Etheridge, Leonie
Due to the ever-growing requirement for chiral compounds, new conditions for stereoselective synthesis are in constant development. Asymmetric organocatalysis is well-studied, with peptide catalysts popular due to their modular and highlyfunctionalisable nature. One such example of their utility is in the Michael reaction, a well-studied carbon-carbon bond forming reaction. [2.2]Paracyclophane is an aromatic industrial precursor compound with remarkable structural and electronic properties. Its conformational bulk and rigidity make it an attractive target for integration into sterically-hindered unnatural amino acids for incorporation into peptides that may be effective organocatalysts. An updated route to 4-amino-13-[2.2]paracyclophane-carboxylic acid (Pca) was developed and optimised. The synthetic route comprises four steps with an overall yield of 50%. This compares with previous routes which had yields between 7 and 48% for 6 - 7 steps. Peptide coupling conditions for the poorly-reactive Pca were developed with some success; including devising a route for direct synthesis of a glycine residue on Pca’s aniline. Four new Pca-containing peptides were described. The above work sets the stage for development of interesting new planar chiral peptide compounds with diverse chemistry. Three Pca-containing peptides were studied as asymmetric organocatalysts in Michael addition between trans-β-nitrostyrene and hexanal and were compared to proline, a known catalyst for this reaction. These tests were performed to probe the relationship between relative conformation between the carboxylic acid and amine moieties of the catalyst, and the catalyst’s stereoselectivity. The Pca-containing catalysts showed an interesting trend to reversal of the prevailing syn product configuration.
Single palladium sites supported on carbon capsules : synthesis, structure, and catalysis : a thesis presented in partial fulfilment of the requirements of the degree of Masters of Science in Chemistry at Massey University, Manawatu, New Zealand
(Massey University, 2019) Olive, Nicholas; Symon, Nicholas
This work investigates the impregnation of palladium into hollow carbon capsules through a novel synthesis method. This work investigates the feasibility of the method, improves on the method and suggests further improvements. The formation of palladium nanoparticles in hollow carbon capsules is investigated by varying the loading of palladium. This is further investigated by demonstrating the effect of other synthesis variables. The synthesized single palladium sites supported on hollow carbon capsules are then investigated for catalytic activity. These catalysts were found to be catalytically active for the Suzuki coupling reaction.
Kinetics and mechanism of proteolytic enzyme catalysed reactions : a thesis presented for the degree of Doctor of Philosophy in Biochemistry
(Massey University, 1973) Boland, Michael John
The enzyme actinidin has been purified and studied chemically and kinetically. The enzyme has many structural and kinetic similarities with ficin and papain. Specificity studies indicate a strong preference for a basic side chain in the S1 site, and competitive inhibitor binding shows a preference for an aromatic group in the S2 site. Inactivation studies show the presence of one active thiol group per enzyme molecule. The hydrolysis of Nα-carbobenzoxy-L-lysine p-nitrophenyl ester by actinidin has been studied in detail. The Michaelis constant, Km, is dependent on groups ionising at pH 3.75 and 8.1. The turnover number, kcat, shows little pH dependence at low pH but an upward inflection dependent on a group ionising at pH 8.1. When the reaction is followed with enzyme concentration in excess of substrate concentration a biphasic reaction is observed. This is interpreted by a mechanism similar to that proposed for ficin and papain catalysed hydrolyses of this substrate. This mechanism is more complicated than the simple acylation-deacylation mechanism normally expected, involving an isomerisation of some kind. Microscopic rate constants for the reaction have been calculated. The significance of various physico-chemical principles of catalysis has been discussed in relation to enzymic catalysis. From a study of the imidazole catalysed hydrolysis of N,O-diacetylserinamide, it has been concluded that general base catalysis could play a much greater part in enzymic catalysis than had previously been estimated.

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