Synthesis and biolgical screening of potential plasmodium falciparum DXR inhibitors
- Authors: Adeyemi, Christiana Modupe
- Date: 2017-04
- Subjects: Plasmodium falciparum , Enzyme inhibitors , Malaria , Antimalarials , Drug development , Malaria -- Chemotherapy , Isopentenoids -- Synthesis , Fosmidomycin , 1-Deoxy-D-xylulose 5-phosphate
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/61790 , vital:28060
- Description: The non-mevalonate isoprenoid pathway, also known as the 1-deoxy-D-xylulose-5- phosphate DXP pathway, is absent in humans, but present in the anopheles mosquito responsible for the transmission of malaria. DXP reductoisomerase - a key enzyme in the DXP pathway in Plasmodium falciparum (PfDXR) has been identified as a target for the design of novel anti-malarial drugs. Fosmidomycin and its acetyl analogue (FR900098) are known to be inhibitors of PfDXR and, in this study, synthetic variations of the fosmidomycin scaffold have led to four series of novel analogues. Particular attention has been centred on the introduction of various substituted benzyl groups in each of these series in order to occupy a recently discovered vacant pocket in the PfDXR active-site and thus enhance ligand-enzyme binding. In the process 160 ligands and precursors have been prepared, no less than 119 of them novel. Fistly, a series of C-benzylated phosphonate esters and phosphonic acids were synthesised, in which the fosmidomycin hydroxamate Mg2+- coordinating moiety was replaced by an amide funtionality and the number of methylene groups in the “hydrophobic patch” between the phosphonate and the hydroxamate moiety was decreased from two to one. Several approaches were explored for this series, the most successful involving reaction of 3- substituted anilines with a-bromo propanoic acid in the presence of the coupling agent 1,1'- carbonyldiimidazole (CDI), followed by Michaelis-Arbuzov phosphonation using triethyl phosphite. Reaction of the resulting chiral phosphonate esters with bromotrimethylsilane gave the corresponding phosphonic acids in good yields. In order to obviate chirality issues, a second series of potential “reverse” fosmidomycin analogues was synthesised by replacing the methylene group adjacent to the the phosphonate moiety with a nitrogen atom. Deprotonation, alkylation and phosphorylation of various amines gave diethyl #-benzylphosphoramidate ester intermediate. Aza-Michael addition of these intermediates, followed by hydrolysis gave the corresponding carboxylic acids which could be reacted with different hydroxylamine hydrochloride derivatives to afford the novel hydroxamic acid derivatives in good yields. Thirdly, a series of a novel #-benzylated phosphoramidate derivatives were prepared as aza- FR900098 analogues. Alkylation of different amines using bromoacetalde-hyde diethylacetal gave a series of N-benzyl-2,2-diethoxyethylamine compounds, which were then elaborated via a futher six steps to afford novel #-benzylated phosphoramidate derivatives. Finally, in order to ensure syn-orientation of the donor atoms in the Mg - coordinating group and, at the same time, introduce conformational constraints in the ligand, the hydrophobic patch and the hydroxamate moiety were replaced by cyclic systems. Several approaches towards the synthesis of such conformationally constrained phosphoramidate analogues from maleic anhydride led to the unexpected isolation of an unprecedented acyclic furfuryl compound, and 1H NMR and DFT-level theoretical studies have been initiated to explore the reaction sequence. A series of #-benzylated phosphoramidate derivatives containing dihydroxy aromatic rings (as the conformationally constrained groups) to replace the hydroxamate moiety, were successfully obtained in six steps from the starting material, 3,4-dihydroxylbenzaldehyde. While in vitro assays have been conducted on all of the synthesised compounds, and some of the ligands show promising anti-malarial inhibitory activity - most especially the conformationally constrained cyclic #-benzylated phosphoramidate series. Interestingly, a number of these compounds has also shown activity against T.brucei - the causative agent of sleeping sickness. In silico docking studies of selected compounds has revealed the capacity of some of the ligands to bind effectively in the PfDXR active-site with the newly introduced benzyl group occupying the adjacent vacant pocket. The physico-chemical properties of these ligands were also explored in order to predict the oral-bioavailability. Most of the ligands obeyed the Lipinski rule of 5, while QSAR methods have been used in an attempt to correlate structural variations and calculated molecular properties with the bioassay data. , Thesis (PhD) -- Faculty of Science, Chemistry, 2017
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- Date Issued: 2017-04
A new synthetic approach for preparation of Efavirenz
- Authors: Chada, Sravanthi
- Date: 2017
- Subjects: Antiretroviral agents , Asymmetric synthesis , Enzyme inhibitors , HIV (Viruses) -- Enzymes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/15512 , vital:28265
- Description: Efavirenz, a drug that is still inaccessible to millions of people worldwide, is potent non nucleoside reverse transcriptase inhibitor (NNRTI), is one of the preferred agents used in combination therapy for first-line treatment of the human immunodeficiency virus (HIV). NNRTIs attach to and block an HIV enzyme called reverse transcriptase, by blocking reverse transcriptase; NNRTIs prevent HIV from multiplying and can reduce the amount of HIV in the body. Efavirenz can't cure HIV/AIDS, but taken in combination with other HIV medicines (called an HIV regimen) every day helps people with HIV live longer healthier lives. Efavirenz also reduces the risk of HIV transmission and can be used by children who are suffering from HIV/AIDS. All the above therapeutic uses of efavirenz prompted us to identify the novel and hopefully cost efficient synthetic methodology for the preparation of efavirenz. In this thesis a new synthetic method for asymmetric synthesis of efavirenz is described. This route started from commercially available starting materials and it is first established in traditional batch chemistry and further the parameters transferred to a semi continuous flow protocol for optimization.
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- Date Issued: 2017
Application of Baylis-Hillman methodology in the synthesis of HIV-1 enzyme inhibitors
- Authors: Manyeruke, Meloddy Hlatini
- Date: 2015
- Subjects: HIV infections , Enzyme inhibitors , AZT (Drug) , Bioconjugates
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4540 , http://hdl.handle.net/10962/d1017920
- Description: The application of Baylis-Hillman methodology has afforded access to a range of β-hydroxypropionate ester-AZT conjugates as potential dual-action HIV-1 IN/RT inhibitors. Two families comprising a total of nine β-hydroxypropionate ester-AZT conjugates were synthesised. The first family was accessed using O-benzylated salicylaldehydes and methyl acrylate and the second from unprotected salicylaldehydes using tert-butyl acrylate as the activated alkene. Spectroscopic methods were employed to fully characterize the compounds. Propargylation of the respective Baylis-Hillman adducts was achieved via conjugate addition of propargylamine. The resulting products were then employed in Cu(I)-catalysed “click” reactions with azidothymidine (AZT) to yield the desired β-hydroxypropionate ester-AZT conjugates. Exploratory studies were also conducted to access 4-hydroxycoumarins from Baylis-Hillman derived adducts and to construct customized chiral Baylis-Hillman reaction sites. Many 4- hydroxycoumarins are known to exhibit a wide range of biological activities, and extending Baylis-Hillman methodology to access these systems is an important challenge. Two approaches were investigated. The first involved the formation of a 4-phthalimidocoumarin, aromatisation and hydrolysis of which was expected to lead to the 4-hydroxycoumarin target. The second, a variation of the first, involved the use of 4-(chrolomethyl)coumarin intermediates. Unfortunately, while various intermediates were prepared and characterised, neither approach led ultimately to the desired targets. N-substituted borneol-10-sulfonamides were constructed from camphor-10- sulfonyl chloride as chiral Baylis-Hillman reaction sites. In a preliminary study, however, none of the N-substituted borneol-10-sulfonamides exhibited Baylis-Hillman catalytic activity.
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- Date Issued: 2015
Design, development and evaluation of novel lead compounds as HIV-1 enzyme inhibitors
- Authors: Sekgota, Khethobole Cassius
- Date: 2015
- Subjects: Enzyme inhibitors , Viruses -- Reproduction , HIV (Viruses)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4546 , http://hdl.handle.net/10962/d1017926
- Description: This project has been concerned with the application of the Baylis-Hillman methodology to the synthesis of medicinally important diketo acid analogues (cinnamate ester-AZT conjugates and 3-hydroxy ester-AZT conjugates) as dual-action HIV-1 IN/RT inhibitors; and on exploratory studies in the preparation of 3-(amidomethyl)-(1H)-2-quinolones as PR inhibitors; and (1H)-2- quinolone-AZT conjugates as dual action IN/RT inhibitors. A series of Baylis-Hillman adducts has been prepared, typically in moderate to excellent yield, by reacting 2-nitrobenzaldehyde with methyl acrylate, ethyl acrylate and methyl vinyl ketone in the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO). Subsequently, various transformations that include conjugate addition of primary and secondary amines to the α,ß-unsaturated moiety to obtain 2- (aminomethyl)-3-hydroxy-3-(2-nitrophenyl)propanoate derivatives, effective SN2´ substitution of the BH ß-hydroxy by a Vilsmeier-Haack in situ-generated chloride to afford Baylis-Hillman allyl chlorides, iron in acetic acid-catalyzed cyclisation to 3-acetoxymethyl-(1H)-2-quinolone derivatives were achieved. Thus, using the Baylis-Hillman methodology, two nuanced classes of diketo acid analogues were constructed. These involved conjugating appropriate propargylamine derivatives with AZT using the „click‟ reaction. In an exploratory study, the quinolone derivative, precisely 3-acetoxymethyl- (1H)-quinol-2-one, was transformed into 3-hydroxymethyl-(1H)-quinol-2-one using potassium carbonate in a mixture of methanol and water (1:1). Following successful hydrolysis, the resulting alcohol was transformed to the corresponding chloride, 3-chloromethyl-(1H)-quinol-2- one, using thionyl chloride. Subsequent nucleophilic substitution afforded 3-(aminomethyl)- (1H)-2-quinolone derivatives which were subsequently transformed to 3-(amidomethyl)-(1H)-2- quinolones; and 3-[(propargylamino)-methyl]-(1H)-quinol-2-one as precursors to quinolone- AZT derivatives. All compounds were characterized by NMR, IR, and where appropriate, high resolution MS
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- Date Issued: 2015
Studies towards the development of novel antimalarial agents
- Authors: Adeyemi, Christiana Modupe
- Date: 2015
- Subjects: Antimalarials , Malaria , Drug resistance , Drug development , Enzyme inhibitors , Plasmodium
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/54645 , vital:26596
- Description: Considerable efforts have been made in the modification of existing antimalarial drugs, and the support of incentive programmes have led to a drastic decrease in malaria cases reported by WHO during the past 6 years. However, the development of drug resistance threatens the eradication of this deadly disease and has prompted research on the synthesis of novel antimalarial drugs. Our research has involved the design and synthesis of novel benzylated phosphonate esters as potential 1-deoxy-D-xylose-5-phosphate reductoisomerase (DXR) inhibitors. A series of amidoalkylphosphonate esters were obtained by reacting various 3-subsituted anilines and heterocyclic amines with chloroalkanoyl chlorides and reacting the resulting chloroalkanamides with triethyl phosphite using Michaelis-Arbuzov methodology. Benzylation of the phosphonate esters afforded a series of novel N-benzylated derivatives in good yields and these compounds were fully characterised by NMR and HRMS methods. Several approaches to the introduction of a benzyl group at the C-2 position of the phosphonate ester derivatives have been explored, leading unexpectedly to the isolation of unprecedented tetrahydrofuranyl derivatives. Studies towards the preparation of potential bi-functional PfDXR / HIV-1 RT inhibitors have also been initiated. Preliminary in silico docking studies of selected non-benzylated and benzylated phosphonated derivatives into the Pf-DXR active-site has provided useful insight into the binding potential of these ligands. Bioassays have revealed a very low toxicity for all the synthesised phosphonated compounds and a number of these ligands also exhibit a promising inhibitory activity against the Plasmodium parasite.
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- Date Issued: 2015
Synthesis and evaluation of novel heterocycles as potential HIV-1 enzyme inhibitors
- Authors: Ngnie Tuemgnie, Gaëlle Tatiana
- Date: 2014
- Subjects: Heterocyclic compounds , Enzyme inhibitors , Organic compounds , Green chemistry , Coumarins , HIV (Viruses) Enzymes
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/194293 , vital:45440 , DOI https://doi.org/10.21504/10962/194293
- Description: This project has focussed on the synthesis and the evaluation of organic compounds as potential HIV-1 enzyme inhibitors, by making use of green chemistry (microwave assisted synthesis and click chemistry), palladium catalyzed reactions (Heck and Sonogashira coupling), Baylis Hillman methodology and aldol condensation. These compounds were synthesized in good yields and fully characterised by spectroscopic techniques. Biological assay data revealed that some of the compounds possess high inhibitory activity and their effective inhibitory concentration was as good as those of drugs in clinical use. These potential drug molecules were identified by preliminary investigations carried out by molecular modelling where a trend of their inhibitory activity against different enzymes was anticipated. Benzotriazole-AZT conjugates generated by 1,3-dipolar cycloaddition of anthranilic acid derivatives with AZT showed good inhibitory activity in silico against both HIV-1 protease (PR) and HIV-1 reverse transcriptase (RT) enzymes. Still in line with our dual action strategy, cinnamate ester-AZT conjugates were synthesized in three steps starting from benzaldehyde derivatives with a click reaction at the final step. These compounds also showed some inhibitory activity against HIV-1 RT enzyme (88%). In addition, the cinnamoyl fragment attached to AZT appeared to improve the activity of AZT against HIV-1 RT. Peptide chemistry involving carbonyl diimidazole as a coupling reagent between cinnamic acid derivatives and protected amino acids was used to prepare substituted amino acid derivatives which appeared to be very active against the integrase (IN) enzyme (88%). Commercially available coumarin was iodinated and derivatized through palladium catalyzed Heck and Sonogashira reactions with activated alkenes and a terminal alkyne respectively to afford novel coumarin derivatives in good yields. Optimization studies on the Heck reaction with regards to the phosphine ligand, the palladium catalyst and the solvent were carried out to afford novel formyl substituted cinnamate esters with nonaflyl salicylaldehyde derivatives. , Thesis (PhD) -- Faculty of Science, Chemistry, 2014
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- Date Issued: 2014
Inhibitory potential of honey on the enzymatic activity of Helicobacter pylori urease
- Authors: Matongo, Fredrick
- Date: 2012
- Subjects: Honey , Helicobacter pylori infections , Enzyme inhibitors , Traditional medicine , Antifungal agents
- Language: English
- Type: Thesis , Masters , MSc (Biochemistry)
- Identifier: vital:11253 , http://hdl.handle.net/10353/431 , Honey , Helicobacter pylori infections , Enzyme inhibitors , Traditional medicine , Antifungal agents
- Description: Urease of Helicobacter pylori is an important virulence factor implicated in the pathogenesis of many clinical conditions, such as chronic gastritis, peptic ulceration, and gastric cancer. Many urease inhibitors have been discovered, like phosphorodiamidates, hydroxamic acid derivatives, and imidazoles. Despite good activities at the enzyme level and excellent kinetic properties most of them have not been used as therapeutic agents in vivo because of their side effects, toxicity and instability. This has led to much attention to focus on exploring the novel urease inhibitory activities of natural products because of their low toxicity and good bioavailability. Honey, a natural product has been used in folk medicine due to its antitumor, antioxidant, antimicrobial and anti-inflammatory properties. The aims of this study were to isolate, characterise, purify urease produced by H. pylori and investigate the inhibitory effects of solvent honey extracts on its enzymatic activity. Urease was found to be both surface-associated and cytoplasmic. Maximum cytoplasmic urease activity was found to occur after 72 hr whereas maximum extracellular urease activities were found to occur after 96 hr. Characterization of the crude cytoplasmic urease revealed optimal activity at a pH of 7.5 and temperature of 40°C. The kinetic parameters Vmax and Km were 45.32 U ml-1 and 61.11 mM respectively.The honey extracts inhibited the activity of the crude urease in a concentration dependent manner. The Lineweaver-Burk plots indicated a non-competitive type of inhibition against H. pylori urease. The two honey extracts gave promising inhibitory activities against urease of H. pylori. Thus the results of this study delineates that inhibition of urease can ease development in therapeutic and preventative approaches based on the enzymatic activity of this Helicobacter protein.
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- Date Issued: 2012
The allelopathic potential of Arctotis Arctotoides (L.f.) O. Hoffm on some vegetables
- Authors: Badmus, Abimbola Adesile
- Date: 2012
- Subjects: Allelopathy , Allelopathic agents , Vegetables -- Microbiology , Enzyme inhibitors
- Language: English
- Type: Thesis , Doctoral , PhD (Botany)
- Identifier: vital:11306 , http://hdl.handle.net/10353/454 , Allelopathy , Allelopathic agents , Vegetables -- Microbiology , Enzyme inhibitors
- Description: Laboratory and greenhouse experiments were conducted to evaluate the allelopathic effects of the extracts and residue Arctotis arctotoides (L.f.) O. Hoffm on selected vegetable crops. The study aimed to address the following specific objectives to (i) examine the ultra structures of the leaf of A. arctotoides using the Scanning Electron Microscope (SEM), (ii) carry out comprehensive qualitative and quantitative phytochemical analysis of the root and shoot materials of the plant, (iii) investigate the allelopathic activities of the root and shoot aqueous extracts of A. arctotoides at concentrations of 10, 8, 6, 4 and 2 mg/ml on germination, radicle and plumule growth of cabbage, carrot, tomato and spinach, (iv) evaluate the inhibitory effects of the dried shoot residue of the plant at 10, 20 and 40 g kg-3 of soil (treatments B, C and D) and the control (treatment A) on the morphology, growth and chlorophyll pigment content of tomato and cabbage transplants at 1, 2, 3 and 4 weeks after transplanting and (v) assess the effects of the dried shoot residue of A. arctotoides on the yield, nutrient uptake by the leaves of tomato and cabbage at 4 and 12 weeks after transplanting. Finally, to analyze the residual mineral content of the soils with tomato and cabbage transplants at 12 weeks after transplanting. The the SEM revealed that anisocytic stomata and glandular trichomes (GTs) were numerous on the abaxial than the adaxial surfaces of A. arctotoides. The non glandular trichomes (NGTs) were also present on both surfaces but lesser on the abaxial. Morphologically, the GTs were peltate, uniseriate and globular head while the NGTs were cylindrical and filamentous with variable number of cells at the basal portion. The energy dispersive X-ray spectroscopy of some crystals showed that Na+ Mg2+ and Ca2+ were the major constituents of the crystal deposit found around the GTs and stomata. The results of the phytochemical composition of the root and shoot extracts of A. arctotoides confirmed the occurrence of alkaloids, flavonoids, phenolics, saponnins, tannins and triterpenes as the common constituents. In addition, cardiac glycosides and steroids were also detected in the shoot of the A. arctotoides. Quantitative estimation of the chemical constituents of the crude extracts further revealed that the alkaloid content in the root higher (0.97 percent) than the shoot (0.64 percent). The quantity of flavonoids detected in the shoot (1.02 percent) was more than that observed in the root (0.35 percent). Others (phenolics and tannins) were marginal in the two plant parts. The results of the inhibitory effects of the root and shoot aqueous extract at the varying concentrations showed that root extract at 10 mg/ml considerably reduced the germination of cabbage, carrot, tomato and spinach seeds by 84.0, 83.2, 72.8 and 37.4 percent respectively. Incubation of the shoot extract at the same concentration resulted in 100 percent inhibition of cabbage and carrot seed germination whereas those of tomato and spinach were suppressed by 91.5 and 61.2 percent respectively. The two extracts at the varying concentrations also had a significant reduction on the radicle and plumule growth of the four vegetables. Addition of the shoot residue to the soil showed massive chlorosis, necrotic lesions and wilting of tomato and cabbage leaves under treatments C and D at 2 weeks after transplanting. The number of leaves, leaf area, dry shoot and root weight of the two vegetables grown in the amended soils were also drastically reduced. The inhibition percentages due to the addition of the three concentrations of A. arctotoides dried shoot residue on the dry shoot weight at 4 weeks after transplanting were 38.6, 45.5 and 70.3. for tomato and 57.5, 73.3 and 87.5 percent for cabbage. Similarly, the declines in the dry root weight of 61.3, 82.9.4 and 83.4 percent for tomato as well as 53.1, 54.7 and 67.2 percent for cabbages were recorded for the two vegetables under treatment B, C and D during the period. The results further showed that the dry fruit yield and shoot weight of tomato under the treatments B, C and D decreased with increase in shoot residue concentrations of A. arctotoides. Relative to treatment A, no significant differences were recorded in the dry head weight of cabbage under the residue treated groups. The reductions in the fruit yield and fresh head weight caused by treatments C and D were 37.2 and 84.8 percent for tomato and 30.9 and 72.4 percent for cabbage. The findings on the mineral contents in the leaves of the two vegetables revealed significant differences in the uptake of N, Mg, Na, Cu and Fe by tomato leaves. The concentrations of N, K, Na and Zn in cabbage leaves also differed. However, the P content was relatively constant in the leaves of the two vegetables at 4 and 12 weeks after transplanting. At 12 weeks after transplanting, the Fe content in soils with tomato and cabbage treatments C and D was greatly enhanced in comparison with the other nutrients. The residual N, P and Zn detected in soils planted to cabbage were similarly equal among all the groups including the control. Thus, under the greenhouse experiment, Arctotis arctotoides (L.f) O. Hoffm has been shown to contain some phytotoxic chemical compounds in its root and shoot materials. The compounds either singly or collectively have demonstrated some inhibitory potentials on the germination, growth and yields of cabbage, carrot, tomato and spinach evaluated in this study.
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- Date Issued: 2012
Studies towards the development of novel HIV-1 integrase inhibitors
- Authors: Lee, Yi-Chen
- Date: 2010
- Subjects: HIV infections -- Treatment , HIV (Viruses) , AIDS (Disease) -- Treatment , Nuclear magnetic resonance , Heterocyclic compounds -- Derivatives , Enzyme inhibitors , Chemical inhibitors , Quinoline
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4357 , http://hdl.handle.net/10962/d1005022 , HIV infections -- Treatment , HIV (Viruses) , AIDS (Disease) -- Treatment , Nuclear magnetic resonance , Heterocyclic compounds -- Derivatives , Enzyme inhibitors , Chemical inhibitors , Quinoline
- Description: The project has focused on the preparation of several series of compounds designed as potential HIV-1 integrase inhibitors. Various 2-nitrobenzaldehydes have been reacted with two activated alkenes, methyl vinyl ketone (MVK) and methyl acrylate, under Baylis-Hillman conditions to afford α-methylene-β-hydroxylalkyl derivatives in moderate to excellent yields. The reactions were conducted using the tertiary amine catalysts, 1,4-diazabicyclo[2.2.2]octane(DABCO) or 3-hydroxyquinuclidine (3-HQ) with chloroform as solvent, and yields were optimised by varying the catalyst, reagent concentrations and the reaction time. Reductive cyclization of the Baylis-Hillman adducts via catalytic hydrogenation, using 10% palladiumon-carbon catalyst in ethanol, afforded quinoline and quinoline N-oxide derivatives. In some cases “acyclic” reduction products were also isolated. Reaction of the Baylis-Hillman MVK adducts with HCl, has resulted in effective nucleophilic (SN’) displacement of the hydroxyl group to afford allylic chloride derivatives. Direct substitution of these chloro derivatives by secondary or primary amines, followed by catalytic hydrogenation gave quinoline derivatives containing a 3-aminomethyl substituent. The Baylis-Hillman ester adducts obtained from reaction with methyl acrylate were treated directly with various amines to give diastereomeric conjugate addition products. Reactions with piperazine gave N,N’-disubstituted piperazine products. The piperidine derivatives have been dehydrated to give cinnamate esters in moderate yields. The products, which have all been satisfactorily characterised by elemental (HRMS) and spectroscopic (1- and 2-D NMR) analysis, constitute a “library” of compounds for in silico and in vitro studies as potential HIV integrase inhibitors.
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- Date Issued: 2010