Faculty of Applied Sciences

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Synthesis, characterisation and biological activity of selected pyrazoles and naphthyrides
(2019) Makhanya, Talent Raymond; Gengan, Robert Moonsamy
The world continue to be threaten by various diseases from viruses, fungi and bacteria that cannot be cured. This arises due to the emergency of multidrug resistance in microorganisms hence current available drugs are becoming less potent. The solution to overcome this predicament is to further synthesize novel heterocyclic compounds which can display good therapeutic properties. Hence, this study focuses on the synthesis, characterization and biological evaluation of selected novel naphthyridinones, naphthyridines and pyrazoles. A total of 53 novel compounds were prepared by using multi-component reactions (MCRs), Povarov’s [4+2] and Povarov’s [3+2] reactions. The MCR was used for a solvent free synthesis of eight novel [1, 8] naphthyridinones from a mixture of 2-aminopicoline, various benzaldehyde derivatives and dimedone. A conventional heating protocol was used whilst the reaction was catalysed by phosphotungstic acid. The compounds were identified as 4, 8, 8-trimethyl-5- phenyl-5, 5a, 8, 9-tetrahydrobenzo[b] [1, 8] naphthyridin-6(7H)-ones with the aid of spectroscopic techniques, viz., FT-IR, NMR, EI- MS and elemental analysis. These eight compounds were screened for their anticancer activity against A549 lung cancer cells. Cell viability assays showed these compounds have a biological effect at various concentrations. Two compounds showed that good potential as an anti-proliferative agent and exhibited a dose- dependent decline in cell viability which was seen. The Povarov’s [4+2] cycloaddition reaction was used to synthesize nine novel fused indolo [1, 8] naphthyridines. Indole was used as the dienophile whilst N-aryl aldimines were selected as the diene which were produced by reacting 2-amino-4-picoline and benzaldehyde. The reaction was catalysed by indium chloride to produce 1-methyl-6-phenyl-6,6a,7,11b-tetrahydro-5H-indolo[3,2-c][1,8]naphthyridine which was characterized by FT-IR, NMR, TOF-MS and elemental analysis. Furthermore, all synthesized compounds were screened for their antimicrobial activity. The results of the bioassay demonstrated that some fused indolo [1, 8] naphthyridines exhibited good inhibitory effect with an MIC value ranging from 0.04687 to 0.09375 µM against Bacillus cereus and Staphylococcus aureus. The toxicity of the synthesized compounds were evaluated through mutagenicity test against Salmonella typhimurium TA 98 and TA100 strains. All compounds showed no mutagenic effects against Salmonella tyhphimurium TA 98 and TA 100 strains. The Povarov’s [3+2] cycloaddition was used to synthesize twenty six novel fused indolo pyrazole in the presence of a catalytic amount of indium chloride. The compounds were identified as 3- phenyl-2, 3-dihydropyrazolo [3, 4-b] indole-1(4H)-carbothioamides with the aid of spectroscopic techniques such as FT-IR, NMR and TOF-MS. All compounds were screened for their antimicrobial activity against various strains of pathogenic bacteria and fungi. These compounds showed good activity against Candida albicans, Candida utilis, and Saccharomyces cerevisiae with MIC of 1.5; 1.1 and 0.375 µM respectively. In addition, all the compounds showed no mutagenic activity against Salmonella tyhphimurium TA 98 and TA100 strains. The scope of the Povarov’s [3+2] reaction was further investigated using isoniazid to synthesise ten novel nicotinyl fused indolo pyrazoles in the presence of a catalytic amount of indium chloride. These compounds were identified as (3-phenyl-2,3- dihydropyrazolo[3,4-b]indol-1(4H)-yl)(pyridin-4-yl)methanone with the aid of spectroscopic techniques such as FT-IR, NMR and TOF-MS. All compounds were screened for their antimicrobial activity against various strains of pathogenic bacteria and fungi. The synthesized compounds showed weak activity against Streptococcus faecalis, Micrococcus luteus and Bacillus coagullans with a zone inhibition diameter of 9 mm and MIC of 0.75 µM. Furthermore, all synthesized compounds were tested for their toxicity against Salmonella tyhphimurium TA 98 and TA100 strains: none showed mutagenic activity.
Thermodynamic properties of phosphonium-based ionic liquid mixtures at different temperatures
(2018) Kabane, Bakusele; Redhi, Gan G.
Ionic Liquids (ILs) are relatively newly formed types of solvents. As part of ongoing research, research groups and industries are focusing on solvents classified as ionic liquids, which have a low melting point,and they have been given great attention focusing on their thermophysical properties and applications. In order to utilize or industrially exploit these types of solvents, the understanding of intermolecular interactions and properties of pure liquids and their mixtures is important. Thermophysical properties of ionic liquid mixtures, especially density, viscosity and speed of sound are measured as a function of temperature. Accurate analysis on thermophysical properties of ionic liquids is more of paramount interest as they indicate the transformation of ionic liquids from small laboratory level to large-scale industrial implementation.In this study, new data for the binary mixtures containing {trihexyltetradecylphosphonium chloride ([P+14, 6, 6, 6] [Cl-]) IL and propanoic acid (PA)} and {1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]) + benzaldehyde or ethyl acetoacetate} were investigated under atmospheric pressure (p equivalent to 0.1 MPa) and at temperatures (293.15 to 313.15) K. Densities (ρ),viscosities (𝜂) as well as speeds of sound (𝑢)were measured over the whole range of mole fraction (𝑥𝑖= 0 to 1). The computed excess properties which includes excess molar volumes(𝑉mE), apparent molar volume (𝑉𝜙),intermolecular free length (Lf), isentropic compressibility(𝑘𝑠), deviations in viscosity (Δ𝜂), apparent molar isentropic compressibility (𝐾𝜙) and deviation in isentropic compressibility(Δ𝑘𝑠)were computed from the experimentally determined data of densities, viscosities and speeds of sound. In addition, measurements of activity coefficients at infinite dilution forvolatile organic compounds (alkenes, alcohols, alkanes, cycloalkanes, aromatic hydrocarbons, thiophene, ketones, acetonitrile, water and tetrahydrofuran) in the IL [trihexyltetradecylphosphonium-bis-(2, 4,4-trimethylpentyl)-phosphinate and trihexyltetradecylphosphonium chloride] were conducted at different temperatures.The obtained results and derived properties have been elucidated in terms of the interactions taking place among the solvent systems.
{2-[(1,3-Benzothiazol-2-yl)methoxy]-5- bromophenyl}(phenyl)methanone
(International Union of Crystallography, 2013) Venugopala, Katharigatta Narayanaswamy; Nayak, Susanta K.; Odhav, Bharti
In the title compound, C21H14BrNO2S, the dihedral angle between the planes of the benzothiazole and phenylmethanone groups is 63.4 (2)°. In the crystal, pairs of C-H...N hydrogen bonds link the molecules to form inversion dimers, which are further linked by C-H...O interactions into chains along the c axis. C-H...[pi] and [pi]-[pi] interactions [centroid-centroid distance = 3.863 (1) Å] further stabilize the molecular assembly.
2-(4-Bromoanilino)-6-(4-chlorophenyl)-5-methoxycarbonyl-4- methyl-3,6-dihydropyrimidin-1-ium chloride
(International Union of Crystallography, 2013-03-09) Venugopala, Katharigatta Narayanaswamy; Nayak, Susanta K.; Odhav, Bharti
In the title molecular salt, C19H18BrClN3O2+·Cl-, the dihedral angles between the pyrimidine ring and the chlorobenzene and bromobenzene rings are 72.4 (2) and 45.5 (2)°, respectively. The dihedral angle between the chlorobenzene and bromobenzene rings is 27.5 (2)°. The conformation of the molecule is stabilized by an intramolecular C-H...O interaction. In the crystal, the anion and cation are linked by an N-H...Cl hydrogen bond. Pairs of weak C-H...O and C-H...Cl hydrogen bonds form inversion dimers. Further N-H...Cl hydrogen bonds form R21(6) motifs and link the dimers into chains along [101]. Br...Cl short contacts [3.482 (2) Å] interlink the hydrogen-bonded chains along the b-axis direction.

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