Synthesis and evaluation of novel HIV-1 enzyme inhibitors
- Authors: Olomola, Temitope Oloruntoba
- Date: 2011
- Subjects: HIV infections -- Treatment HIV infections -- Chemotherapy HIV (Viruses) Enzyme inhibitors AZT (Drug) Reverse transcriptase Proteolytic enzymes Ligands Psoralens Resorcinol
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4369 , http://hdl.handle.net/10962/d1005034
- Description: This study has involved the design, synthesis and evaluation of novel HIV-1 enzyme inhibitors accessed by synthetic elaboration of Baylis-Hillman adducts. Several series of complex coumarin-AZT and cinnamate ester-AZT conjugates have been prepared, in high yields, by exploiting the click reaction between appropriate Baylis-Hillman derived precursors and azidothymidine (AZT), all of which have been fully characterised using spectroscopic techniques. These conjugates, designed as potential dual-action HIV-1 inhibitors, were tested against the appropriate HIV-1 enzymes, i.e. HIV-1 reverse transcriptase and protease or HIV-1 reverse transcriptase and integrase. A number of the ligands have exhibited % inhibition levels and IC50 values comparable to drugs in clinical use, permitting their identification as lead compounds for the development of novel dual-action inhibitors. In silico docking of selected ligands into the active sites of the respective enzymes has provided useful insight into binding conformations and potential hydrogen-bonding interactions with active-site amino acid residues. A series of furocoumarin carboxamide derivatives have been synthesised in four steps starting from resorcinol and these compounds have also been tested for HIV-1 integrase inhibition activity. The structures of unexpected products isolated from Aza-Baylis-Hillman reactions of N-tosylaldimines have been elucidated by spectroscopic analysis, and confirmed by single crystal X-ray analysis. A mechanism for what appears to be an unprecedented transformation has been proposed. Microwave-assisted SeO₂ oxidation of Baylis-Hillman-derived 3-methylcoumarins has provided convenient and efficient access to coumarin-3-carbaldehydes, and a pilot study has revealed the potential of these coumarin-3-carbaldehydes as scaffolds for the construction of tricyclic compounds. The HCl-catalysed reaction of tert-butyl acrylate derived Baylis-Hillman adducts has been shown to afford 3-(chloromethyl)coumarins and α-(chloromethyl)cinnamic acids, the Zstereochemistry of the latter being established by X-ray crystallography. ¹H NMR-based experimental kinetic and DFT-level theoretical studies have been undertaken to establish the reaction sequence and other mechanistic details. Base-catalysed cyclisation on the other hand, has been shown to afford 2H-chromene rather than coumarin derivatives.
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Synthesis of novel inhibitors of 1-Deoxy-D-xylulose-5-phosphate reductoisomerase as potential anti-malarial lead compounds
- Authors: Mutorwa, Marius Kudumo
- Date: 2011
- Subjects: Antimalarials -- Development Plasmodium falciparum Malaria -- Chemotherapy Drug development Lead compounds Phosphonates Phosphonic acids Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4372 , http://hdl.handle.net/10962/d1005037
- Description: This research has focused on the development of novel substrate mimics as potential DXR inhibitors of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR), an essential enzyme in the mevalonate-independent pathway for the biosynthesis of isoprenoids in Plasmodium falciparum. DXR mediates the isomerisation and reduction of 1-deoxy-D-xylulose-5-phosphate (DOXP) into 2C-methyl-D-erithrytol 4-phosphate (MEP) and has been validated as an attractive target for the development of novel anti-malarial chemotherapeutic agents. Reaction of various amines with specially prepared 4-phosphonated crotonic acid in the presence of the peptide coupling reagent, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), has afforded a series of amido-phosphonate esters in moderate to good yields (48% - 73%) which, using a RuCl₃/CeCl₃/NaIO₄ catalyst system, have been dihydroxylated to furnish the dihydroxy-amido phosphonate ester pro-drugs; subsequent hydrolysis under microwave irradiation has afforded the corresponding phosphonic acids. A second series of potential inhibitors viz., 3-substituted aniline-derived phosphonate esters, their corresponding phosphonic acids and mono-sodium salts, have also been successfully synthesised. In these compounds, the essential functional groups are separated by one, two, three or four methylene groups, Deprotonation of the 3-substituted aniline substrates, followed by reaction with the appropriate ω-chloroalkanoyl chloride produced the ω-chloroamide intermediates, which were subjected to the Michaelis-Arbuzov reaction to afford the diethyl phosphonate esters in moderate to good yields (48% - 74%). Microwave-assisted TMSBrmediated cleavage of the phosphonate esters furnished the phosphonic acids, neutralisation of which afforded the mono-sodium salts. Furan-derived phosphate esters and phosphonic acids have been prepared as conformationally-restricted DOXP analogues. Functionalization at C-5 of the trityl-protected furan was achieved using the Vilsmeier-Haack formylation and Friedel-Crafts acylation reactions and, following de-tritylation, phosphorylation and oximation, using hydroxylamine hydrochloride, the novel oxime derivatives have been isolated as a third series of potential DXR inhibitors in very good yields (87% - 96%). Finally, in order to exploit an additional binding pocket in the PƒDXR active site, a series of N-benzylated phosphoramidic derivatives were obtained in seven steps from the starting material, diethyl phosphoramidate. The known inhibitors, fosmidomycin and its acetyl derivative FR900098, were also successfully synthesised as standards for STD-NMR binding and inhibition assays. In all, over 200 compounds (136 novel) have been prepared and appropriately characterised using 1-and 2-D NMR and IR spectroscopic analysis and, where necessary, HRMS or combustion analysis. Saturation Transfer Difference (STD) protein-NMR experiments, undertaken using selected compounds, have revealed binding of most of the ligands examined to EcDXR. Computersimulated docking studies have also been used to explore the preferred ligand-binding conformations and interactions between the ligands and essential DXR active-site residues, while DXR-enzyme inhibition assays of selected synthesised ligands have revealed certain patterns of inhibitory activity.
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The design and synthesis of multidentate N-heterocyclic carbenes as metathesis catalyst ligands
- Authors: Truscott, Byron John
- Date: 2011
- Subjects: Carbenes (Methylene compounds) , Heterocyclic compounds , Ligands , Ligands -- Design , Metathesis (Chemistry) , Catalysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4304 , http://hdl.handle.net/10962/d1004962 , Carbenes (Methylene compounds) , Heterocyclic compounds , Ligands , Ligands -- Design , Metathesis (Chemistry) , Catalysis
- Description: This study has focused on the design and preparation of bi– and tridentate N–Heterocyclic Carbene (NHC) ligands in order to investigate the effect of a multidentate approach to the formation, stability and catalytic activity of coordination complexes. Chapters 1 – 3 provide background information of relevant catalysis, carbene and coordination chemistry, followed by previous work performed within our research group. In Chapter 4 attention is given to the synthetic aspects of the research conducted, comprising two distinct approaches to the preparation of unsymmetrical saturated and unsaturated NHCs. Firstly, an investigation of the saturated NHC ligands yielded three novel, unsymmetrical pro–ligands, viz., two halopropyl imidazolinium salts and a bidentate hydroxypropyl imidazolinium salt. Secondly, eight imidazolium salts have been generated, including a hydroxypropyl analogue and novel decyl and tridentate malonyl derivatives. These compounds were prepared using microwave–assisted methodology for the alkylation of N– mesitylimidazole – an approach that drastically reduced reaction times (from 8 hours – 7 days to ca. 0.5 – 2 hours) and facilitated isolation of the imidazolium salts. Many of the compounds prepared in this study are novel and were fully characterized using HRMS and 1– and 2–D NMR analysis. Coordination studies using a selection of the prepared pro–ligands afforded an alkoxy–NHC silver derivative and four novel Ru–complexes, viz., Grubbs II–type Ru–complexes containing:– chloropropyl imidazolinylidene; propenyl imidazolylidene; and bidentate alkoxypropyl imidazolylidene ligands. Furthermore, a well–defined benzyl mesitylimidazolylidene Ru–complex has been isolated, which exhibited good stability in air. DFT–level geometry–optimization studies, using the Accelrys DMol3 package have given valuable insights into the likely geometries of the prepared and putative catalysts.
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