A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 28 May 2018. / Since their discovery, protease inhibitors continue to be an essential component of antiretroviral treatment for human immunodeficiency virus type 1 (HIV-1). However, the development of resistance to protease inhibitors remains one of the most significant challenges in the fight for sustained viral suppression in those infected with HIV-1. Studies show that specific mutations arising within the HIV-1 gag and protease genes can lead to the development of resistance. In this research, a South African HIV-1 subtype C Gag-protease variant (W1201i) was investigated. This variant was considered due to the presence of a mutation and insertion (N37T↑V), located within the hinge region of the protease enzyme. Moreover, the variant displayed the following polymorphisms: Q7K, I13V, G16E, M36T, D60E, Q61E, I62V and M89L. Genotyping of W1201i Gag revealed a previously unreported MSQAG insertion between the CA/p2 and p2/NC cleavage sites. Additionally, a mutation and insertion (I372L↑M), and multiple polymorphisms (S369N, S371N, I373M and G377S) were discovered within the p2/NC cleavage site. Single-cycle phenotypic assays were performed to determine the drug susceptibility and replication capacity of the variant. The results show that the mutations present in the N37T↑V protease conferred a replicative advantage and reduced susceptibility to lopinavir, atazanavir and darunavir. Interestingly, the mutations in W1201i Gag were found to modulate both replication capacity and protease inhibitor susceptibility. In silico studies were performed to understand the physical basis for the observed variations. Molecular dynamics simulations showed that the N37T↑V protease displayed altered dynamics around the hinge and flap region and highlighted the amino acids responsible for the observed fluctuations. Furthermore, induced fit docking experiments showed that the variant bound the iv protease inhibitors with fewer favourable chemical interactions than the wild-type protease. Collectively, these data elucidate the biophysical basis for the selection of hinge region mutations and insertions by the HI virus and show that protease, as well as Gag, needs to be evaluated during resistance testing. / EM2018

Through the SARS-CoV-2 pandemic, it has become clear that the development of antivirals is essential for the health and wellbeing of the population. In this study, novel active site protease inhibitors against SARS-CoV-2 were tested for their inhibitory activity against the viral 3-Chymotrypsin like protease through the means of FRET based enzymatic assays. Additionally, Compound 104 targeting the NS2B-NS3 protease was tested against Zika virus through yield reduction assays as a means to assess whether these assays are suitable for the assessment of peptide hybrid compounds in Zika virus.Novel compounds against SARS-CoV-2 were screened and five of the selected six active compounds were found to inhibit the viral protease at a half-maximal inhibitory concentration (IC50) of below 0.075 µM.In Zika virus, the yield reduction assay was assessed and it was found that under the conditions tested, this assay is not suitable for the assessment of peptide hybrid compounds in Zika virus.The active novel compounds against SARS-CoV-2 should be taken for further assessment in cell based assays as the next step of development. Compound 104 should be assessed under different experimental conditions to identify whether different conditions can make this assay suitable for the intended use.

No description available.

<p>The HIV protease is an essential enzyme for HIV replication and constitutes an important target in the treatment of HIV/AIDS. Efficient combination therapies using inhibitors of the reverse transcriptase and protease enzymes have led many to reevaluate HIV infections from a terminal condition to a chronic-but-manageable disease in the developed world. Unfortunately, the emergence of drug resistant viral strains and severe treatment-related adverse effects limit the benefits of current anti-HIV/AIDS drugs for many patients. Furthermore, less than one in ten patients infected with HIV in low- and middle-income countries have access to proper treatment. These important shortcomings highlight the need for new, cost effective anti-HIV/AIDS drugs with unique properties.</p><p>Microwave heating has recently emerged as a productivity-enhancing tool for the medicinal chemist. Reaction times can often be reduced from hours to minutes or seconds and chemistry previously considered impractical or unattainable can now be accessed.</p><p>In this thesis, the search for unique HIV-1 protease inhibitors and the development and application of new microwave-promoted synthetic methods useful in small-scale medicinal chemistry applications are presented. Protocols for rapid amino- and hydrazidocarbonylations were developed. Mo(CO)₆ was used as a solid source of carbon monoxide, enabling a safe, efficient and simple way to exploit carbonylation chemistry without the direct use of toxic carbon monoxide gas. The aminocarbonylation methodology was applied in the synthesis of two series of new HIV-1 protease inhibitors. A biological evaluation suggested that <i>ortho</i>-substitution of P1 and/or P1’ benzyl side chains might provide a new approach to HIV-1 protease inhibitors with novel properties. To assess the scope and limitations of the <i>ortho</i>-substitution concept, a new series of compounds exhibiting fair potency was prepared by various microwave-heated, palladium-catalyzed coupling reactions. Finally, computer modeling was applied to rationalize the binding-modes and structure-activity relationships of these HIV-1 protease inhibitors.</p>

The HIV protease is an essential enzyme for HIV replication and constitutes an important target in the treatment of HIV/AIDS. Efficient combination therapies using inhibitors of the reverse transcriptase and protease enzymes have led many to reevaluate HIV infections from a terminal condition to a chronic-but-manageable disease in the developed world. Unfortunately, the emergence of drug resistant viral strains and severe treatment-related adverse effects limit the benefits of current anti-HIV/AIDS drugs for many patients. Furthermore, less than one in ten patients infected with HIV in low- and middle-income countries have access to proper treatment. These important shortcomings highlight the need for new, cost effective anti-HIV/AIDS drugs with unique properties. Microwave heating has recently emerged as a productivity-enhancing tool for the medicinal chemist. Reaction times can often be reduced from hours to minutes or seconds and chemistry previously considered impractical or unattainable can now be accessed. In this thesis, the search for unique HIV-1 protease inhibitors and the development and application of new microwave-promoted synthetic methods useful in small-scale medicinal chemistry applications are presented. Protocols for rapid amino- and hydrazidocarbonylations were developed. Mo(CO)6 was used as a solid source of carbon monoxide, enabling a safe, efficient and simple way to exploit carbonylation chemistry without the direct use of toxic carbon monoxide gas. The aminocarbonylation methodology was applied in the synthesis of two series of new HIV-1 protease inhibitors. A biological evaluation suggested that ortho-substitution of P1 and/or P1’ benzyl side chains might provide a new approach to HIV-1 protease inhibitors with novel properties. To assess the scope and limitations of the ortho-substitution concept, a new series of compounds exhibiting fair potency was prepared by various microwave-heated, palladium-catalyzed coupling reactions. Finally, computer modeling was applied to rationalize the binding-modes and structure-activity relationships of these HIV-1 protease inhibitors.

The liver fluke, Fasciola hepatica, is one of the most important parasites of livestock, and it also infects humans. The proteolytic system of trematodes is critical for their interaction with the host and is a potential target for the development of novel vaccines. This work is focused on proteases secreted by F. hepatica adults and on FheCy2, a new protease inhibitor from the cystatin family. The proteolytic activity of the secreted proteases was analyzed using: (a) chromogenic protein substrates and fluorogenic peptide substrates, (b) selective protease inhibitors, and (c) a fluorescent activity-based probe for visualization of proteases. The results showed that the secreted proteases are cysteine proteases of papain family belonging to cathepsins L and B. These proteases were effectivelly inhibited by FheCy2 as demonstrated by enzymological analysis. It can be assumed that FheCy2 participates in the physiological regulation of endogenous proteases secreted by F. hepatica adults, which makes it attractive candidate protein for vaccination studies. Key words: Fasciola hepatica, cathepsins, proteolytic activity, substrate specificity, protease inhibitors (In Czech)

Small chiral molecules are very important building blocks in the synthesis of biologically active compounds. These building blocks include nitrogen and oxygen-containing heterocycles such as 2-oxazolidinones, 1,3-oxazinan-2-ones, 2-oxazolines, oxazines, morpholine and morpholinones. Because of their interesting properties, chiral heterocycles have stirred great interest in the synthetic chemist community to develop useful and efficient strategies to these molecules. In this dissertation, the design and syntheses of various heterocyclic building blocks are presented, as well as the testing of their biological activities as antibacterial. Another very interesting family of heterocycle-containing molecules are the Aeruginosins. They are a family of marine natural products isolated from a blue-green algae, which display inhibitory activity against serine proteases such as thrombin, trypsin, and factor VIIa. Most aeruginosins contain an heterocyclic moiety called the 2-carboxy-6-hydroxyoctahydroindole (Choi) ring; this Choi moiety is a rigid bicyclic unnatural amino acid and is the core structure in the aeruginosins, indispensable to their biological activity. A synthesis of a ring-oxygenated variant of the Choi from D-mannose is reported in this dissertation. The ring-oxygenated variant of 2-carboxy-6-hydroxyoctahydroindole can potentially be used as a surrogate of Choi in the design and synthesis of aeruginosin-based thrombin inhibitors.

<p>This thesis describes the design and synthesis of compounds that are</p><p>intended to inhibit serine and aspartic proteases. The first part of the text deals with preparation of inhibitors of the hepatitis C virus (HCV) NS3 serine protease. Hepatitis C is predominantly a chronic disease that afflicts about 170 million people worldwide. The NS3 protease, encoded by HCV, is essential for replication of the virus and has become one of the main targets when developing drugs to fight HCV. The inhibitors discussed here constitute surrogates for the widely used <em>N</em>-acyl-hydroxyproline isostere designated 4-hydroxy-cyclopentene. The stereochemistry of the 4-hydroxy-cyclopentene scaffold was determined by nuclear overhauser effect spectroscopy (NOESY) and the regiochemistry by heteronuclear multiple bond correlation (HMBC). The scaffold was decorated with different substituents to obtain both linear and macrocyclic HCV NS3 protease inhibitors that display low nanomolar activity. The second part of the thesis describes the design and synthesis of potential aspartic protease inhibitors. The hydroxyethylene motif was used as a noncleavable transition state isostere. The synthetic route yielded a pivotal intermediate with excellent stereochemical control, which was corroborated by NOESY experiments. This intermediate can be diversified with different substituents to furnish novel aspartic protease inhibitors.</p> / Report code: LIU-TEK-LIC-2006:45

Palladium-catalysed coupling reactions have been embraced by synthetic chemists as one of the preferred means for smooth formation of new carbon-carbon bonds: a truly ubiquitous methodology of synthesizing complex molecules. This thesis describes the study of a series of palladium(0)-catalysed C2-arylations of a 1-cyclopentenyl ether, equipped with a chiral (S)-N-methyl-pyrrolidine auxiliary. The investigated olefin was demonstrated to undergo Si-face insertion, providing (R)-configuration of the arylated C2-carbon. In addition, the mild and novel palladium(II)-catalysed dominoHeck/Suzuki β,α-diarylation-reduction of a dimethylaminoethyl-substituted chelating vinyl ether was developed using arylboronic acids as arylating agents in combination with 1,4-benzoquinone (BQ). Further, highly regioselective palladium(II)-catalysed α-and β-monoarylation of the chelating vinyl ether was achieved using either a bidentate ligand or by employing ligand-less conditions. These studies demonstrate that the choice of ligands has a profound effect on the reaction outcome, as productive β,α-diarylation could only be obtained by suppressing the competing β-hydride elimination using BQ as the stabilising ligand and terminal reoxidant. The pivotal role of BQ in the reaction was studied using computer-aided density functional theory calculations. The calculations highlight the crucial role of BQ as a Pd(II)-ligand. In addition of serving as an oxidant of palladium, the calculations support the view that the coordination of BQ to the Pd(II)-centre in the key σ-alkyl complex leads to a low-energy pathway, aided by a strong η2 Pd-BQ donation-back-donation interaction. Furthermore, an investigation of the scope and limitations of novel stereoselective and BQ-mediated palladium(II)-catalysed domino Heck/Suzuki β,α-diarylation reactions, involving metal coordinating cyclic methylamino vinyl ethers and a number of electronically diverse arylboronic acids, conducted. In addition, a set of 4-quinolone-3-carboxylic acids, structurally related to elvitegravir and bearing different substituents on the condensed benzene ring, was designed and synthesized as potential HIV-1 integrase inhibitors. Finally, in an effort to identify a new class of HIV-1 protease inhibitors, four different stereopure β-hydroxy γ-lactam-containing inhibitors were synthesized, biologically evaluated, and co-crystallized with the enzyme. / The time 12:05 for the public defense mentioned in the thesis is incorrect. It will take place at 09:15, 2012-06-08.

This thesis investigates the design, synthesis and biological assay of cysteine protease inhibitors within the papain superfamily of cysteine proteases. This is achieved by examining the effect of inhibitor design, especially warheads, on IC₅₀ values and structureactivity relationships between cysteine protease inhibitors of the papain superfamily. The representative proteases used are m-calpain, μ-calpain, cathepsin B and papain. Chapter One is an introductory chapter; Chapters Two-Four describe the design and synthesis of cysteine protease inhibitors; Chapter Five discusses assay protocol; and Chapter Six contains the assay results and structure-activity relationships of the synthesised inhibitors. Chapter One introduces cysteine proteases of the papain family and examines the structure, physiology and role in disease of papain, cathepsin B, m-calpain and μ-calpain. The close structural homology that exists between these members of the papain superfamily is identified, as well characteristics unique to each protease. Covalent reversible, covalent irreversible and non-covalent warheads are defined. The generic inhibitor scaffold of address region, recognition and warhead, upon which the inhibitors synthesised in this thesis are based, is also introduced. Chapter Two introduces reversible cysteine protease inhibitors found in the literature and that little is known about the effect of inhibitor warhead on selectivity within the papain superfamily. Oxidation of the dipeptidyl alcohols 2.6, 2.26, 2.29, 2.30, 2.35 and 2.36 utilising the sulfur trioxide-pyridine complex gave the aldehydes 2.3, 2.27, 2.19, 2.2, 2.21 and 2.22. Semicarbazones 2.37-2.40 were synthesised by a condensation reaction between the alcohol 2.3 and four available semicarbazides. The amidoximes 2.48 and 2.49 separately underwent thermal intramolecular cyclodehydration to give the 3-methyl-1,2,4- oxadiazoles 2.41 and 2.50. The aldehydes 2.3 and 2.27 were reacted with potassium cyanide to give the cyanohydrins 2.51 and 2.52. The cyanohydrins 2.51 and 2.52 were separately reacted to give 1) the α-ketotetrazoles 2.43 and 2.55; 2) the α-ketooxazolines 2.42 and 2.58; 3) the esterified cyanohydrins 2.60 and 2.61. A two step SN2 displacement reaction of the alcohol 2.6 to give the azide 2.62, an example of a non-covalent cysteine protease inhibitor. Chapter Three introduces inhibitors with irreversible warheads. The well-known examples of epoxysuccinic acids 3.1 and 3.5 are discussed in detail, highlighting the lack of irreversible cysteine protease specific inhibitors. The aldehydes 2.3 and 2.27 were reacted under Wittig conditions to give the α,β-unsaturated carbonyls 3.14-3.18. Horner- Emmons-Wadsworth methodology was utilised for the synthesis of the vinyl sulfones 3.20- 3.23. The dipeptidyl acids 2.24 and 2.28 were separately reacted with diazomethane to give the diazoketones 3.25 and 3.26. The diazoketones 3.25 and 3.26 were separately reacted with hydrogen bromide in acetic acid (33%) to give the α-bromomethyl ketones 3.27 and 3.28, which were subsequently reduced to give the α-bromomethyl alcohols 3.29-3.32. Under basic conditions the α-bromomethyl alcohols 3.29-3.32 ring-closed to form the peptidyl epoxides 3.33-3.36. Chapter Four introduces the disadvantages of peptide-based inhibitors. A discussion is given on the benefits of constraining inhibitors into the extended bioactive conformation known as a β-strand. Ring closing metathesis is utilised in the synthesis of the macrocyclic aldehyde 4.4, macrocyclic semicarbazone 4.15, the macrocyclic cyanohydrin 4.16, the macrocyclic α-ketotetrazole 4.18 and the macrocyclic azide 4.19. Chapter Five introduces enzyme inhibition studies. The BODIPY-casein fluorogenic assay used for establishing inhibitor potency against m-calpain and μ-calpain is validated. Assay protocols are also established and validated for cathepsin B, papain, pepsin and α- chymotrypsin. A discussion of the effect of solvent on enzyme activity is also included as part of this study. Chapter Six presents the assay results for all the inhibitors synthesised throughout this thesis and an extensive structure-activity relationship study between inhibitors is included. The alcohols 2.26 and 2.30 are unprecedented examples of non-covalent, potent, cathepsin B inhibitors (IC₅₀ = 0.075 μM selectivity 80-fold and 1.1 μM, selectivity 18-fold). The macrocyclic semicarbazone 4.15 is an unprecedented example of a potent macrocyclic cysteine protease inhibitor (m-calpain: IC₅₀ = 0.16 μM, selectivity 8-fold). The cyanohydrin 2.51 contains an unprecedented cysteine protease warhead and is a potent and selective inhibitor of papain (IC₅₀ = 0.030 μM, selectivity 3-fold). The O-protected cyanohydrin 2.61 is a potent and selective inhibitor of pepsin (IC₅₀ = 1.6 μM, selectivity 1.5-fold). The top ten warheads for potent, selective cathepsin B inhibition are: carboxylic acid, methyl ester, diazoketone, esterified cyanohydrin, α-bromomethyl ketone, α,β- unsaturated aldehyde, vinyl sulfones, α-bromomethyl-C₃-S,R-alcohol, alcohol and α,β- unsaturated ethyl ester. The selectivity of these warheads was between 5- and 130-fold for cathepsin B. The best inhibitors for cathepsin B were the α-bromomethyl ketone 3.26 (IC₅₀ = 0.075 μM, selectivity 16-fold), the α,β-unsaturated aldehyde 3.18 (IC₅₀ = 0.13 μM, selectivity 13-fold) and the esterified cyanohydrin 3.59 (IC₅₀ = 0.35 μM, selectivity 22- fold). Chapter Seven outlines the experimental details and synthesis of the compounds prepared in this thesis.