Wan-Sin Loh

Structural Correlation of Some Heterocyclic Chalcone Analogues and Evaluation of Their Antioxidant Potential

A series of six novel heterocyclic chalcone analogues 4(a–f) has been synthesized by condensing 2-acetyl-5-chlorothiophene with benzaldehyde derivatives in methanol at room temperature using a catalytic amount of sodium hydroxide. The newly synthesized compounds are characterized by IR, mass spectra, elemental analysis and melting point. Subsequently; the structures of these compounds were determined using single crystal X-ray diffraction. All the synthesized compounds were screened for their antioxidant potential by employing various in vitro models such as DPPH free radical scavenging assay, ABTS radical scavenging assay, ferric reducing antioxidant power and cupric ion reducing antioxidant capacity. Results reflect the structural impact on the antioxidant ability of the compounds. The IC50 values illustrate the mild to good antioxidant activities of the reported compounds. Among them, 4f with a p-methoxy substituent was found to be more potent as antioxidant agent.

Heteroaryl Chalcones: Design, Synthesis, X-ray Crystal Structures and Biological Evaluation

Chalcone derivatives have attracted increasing attention due to their numerous pharmacological activities. Changes in their structures have displayed high degree of diversity that has proven to result in a broad spectrum of biological activities. The present study highlights the synthesis of some halogen substituted chalcones 3(a–i) containing the 5-chlorothiophene moiety, their X-ray crystal structures and the evaluation of possible biological activities such as antibacterial, antifungal and reducing power abilities. The results indicate the tested compounds show a varied range of inhibition values against all the tested microbial strains. Compound 3c with a p-fluoro substituent on the phenyl ring exhibits elevated antimicrobial activity, whereas the compounds 3e and 3f displayed the least antimicrobial activities. The compounds 3d, 3e, 3f and 3i showed good ferric and cupric reducing abilities, and the compounds 3b and 3c showed the weakest reducing power in the series.

Investigation of supramolecular synthons and structural characterisation of aminopyridine-carboxylic acid derivatives

BackgroundCo-crystal is a structurally homogeneous crystalline material that contains two or more neutral building blocks that are present in definite stoichiometric amounts. The main advantage of co-crystals is their ability to generate a variety of solid forms of a drug that have distinct physicochemical properties from the solid co-crystal components. In the present investigation, five co-crystals containing 2-amino-6-chloropyridine (AMPY) moiety were synthesized and characterized.ResultsThe crystal structure of 2-amino-6-chloropyridine (AMPY) (I), and the robustness of pyridine-acid supramolecular synthon were discussed in four stoichiometry co-crystals of AMPY…BA (II), AMPY…2ABA (III), AMPY…3CLBA (IV) and AMPY…4NBA (V). The abbreviated designations used are benzoic acid (BA), 2-aminobenzoic acid (2ABA), 3-chlorobenzoic acid (3CLBA) and 4-nitrobenzoic acid (4NBA). All the crystalline materials have been characterized by 1HNMR, 13CNMR, IR, photoluminescence, TEM analysis and X-ray diffraction. The supramolecular assembly of each co-crystal is analyzed and discussed.ConclusionsExtensive N---H · · · N/N---H · · · O/O---H · · · N hydrogen bonds are found in (I-V), featuring different supramolecular synthons. In the crystal structure, for compound (I), the 2-amino-6-chloropyridine molecules are linked together into centrosymmetric dimers by hydrogen bonds to form homosynthon, whereas for compounds (II-V), the carboxylic group of the respective acids (benzoic acid, 2-aminobenzoic acid, 3-chlorobenzoic acid and 4-nitrobenzoic acid) interacts with pyridine molecule in a linear fashion through a pair of N---H · · · O and O---H · · · N hydrogen bonds, generating cyclic hydrogen-bonded motifs with the graph-set notationR228, to form heterosynthon. In compound (II), another intermolecular N---H · · · O hydrogen bonds further link these heterosynthons into zig-zag chains. Whereas in compounds (IV) and (V), these heterosynthons are centrosymmetrically paired via N---H · · · O hydrogen bonds and each forms a complementary DADA [D = donor and A = acceptor] array of quadruple hydrogen bonds, with graph-set notationR238, R228 and R238.

2-(4-Bromo­phen­yl)-2-oxoethyl 4-meth­oxy­benzoate

In the title compound, C16H13BrO4, the benzene rings are almost perpendicular to each other, making a dihedral angle of 84.07 (8)°. In the crystal, the molecules are linked into chains along the a axis via intermolecular C—H⋯O hydrogen bonds. A C—H⋯π interaction is also observed.

1-(6-Chloro-2-methyl-4-phenyl­quinolin-3-yl)-3-(3-methoxy­phen­yl)prop-2-en-1-one

In the title compound, C26H20ClNO2, the quinoline ring system is approximately planar with a maximum deviation of 0.028 (2) Å and forms a dihedral angle of 73.84 (5)° with the phenyl ring. Two neighbouring molecules are arranged into a centrosymmetric dimer through a pair of intermolecular C—H⋯Cl interactions. A pair of intermolecular C—H⋯O hydrogen bonds link two methoxyphenyl groups into another centrosymmetric dimer, generating an R 2 2(8) ring motif. The structure is further stabilized by C—H⋯π interactions.

Synthesis and Crystal Structures of N-Substituted Pyrazolines

Four pyrazole compounds, 3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole-1-carbaldehyde (1), 5-(4-bromophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehyde (2), 1-[5-(4-chlorophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-1-yl]ethanone (3) and 1-[3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl]propan-1-one (4), have been prepared by condensing chalcones with hydrazine hydrate in the presence of aliphatic acids, namely formic acid, acetic acid and propionic acid. The structures were characterized by X-ray single crystal structure determination. The dihedral angles formed between the pyrazole and the fluoro-substituted rings are 4.64(7)° in 1, 5.3(4)° in 2 and 4.89(6)° in 3. In 4, the corresponding angles for molecules A and molecules B are 10.53(10)° and 9.78(10)°, respectively.

1-[5-(4-Bromo­phen­yl)-3-(4-fluoro­phen­yl)-4,5-dihydro-1H-pyrazol-1-yl]ethanone

In the title molecule, C17H14BrFN2O, the benzene rings form dihedral angles of 6.58 (6) and 85.31 (6)° with the mean plane of the 4,5-dihydro-1H-pyrazole ring (r.m.s. deviation = 0.0231 Å). The latter ring is planar with a maximum deviation of 0.032 (1) Å The dihedral angle between the benzene rings is 78.75 (6)°. In the crystal, weak C—H⋯O and C—H⋯F hydrogen bonds link the molecules into corrugated layers parallel to the ab plane.

1-[5-(4-Bromo-phen-yl)-3-(4-fluoro-phen-yl)-4,5-dihydro-1H-pyrazol-1-yl]butan-1-one.

In the title compound, C19H18BrFN2O, the benzene rings form dihedral angles of 5.38 (7) and 85.48 (7)° with the mean plane of the 4,5-dihydro-1H-pyrazole ring (r.m.s. deviation = 0.0849 Å), which approximates to an envelope conformation with the –CH2– group as the flap. The dihedral angle between the benzene rings is 82.86 (7)°. In the crystal, C—H⋯F and C—H⋯O hydrogen bonds link the molecules to form inversion dimers and together these generate chains along [011]. The crystal packing also features C—H⋯π interactions.

2-(4-Bromo-phen-yl)-2-oxoethyl 4-hy-droxy-benzoate.

In the title compound, C15H11BrO4, the dihedral angle between the aromatic rings is 66.77 (8)°. In the crystal, O—H⋯O, C—H⋯Br and C—H⋯O hydrogen bonds link the molecules, forming layers lying parallel to (101). The crystal packing is further consolidated by C—H⋯π interactions and π–π stacking interactions [centroid–centroid distance = 3.5476 (7) Å].

1-(6-Chloro-2-methyl-4-phenyl-3-quinol­yl)ethanone

In the title compound, C18H14ClNO, the quinoline ring system is approximately planar with a maximum devation of 0.022 (1) Å and forms a dihedral angle of 62.70 (3)° with the phenyl ring. In the crystal, pairs of C—H⋯O intermolecular hydrogen bonds link neighbouring molecules into inversion dimers, forming R 2 2(14) ring motifs. These inversion dimers are stacked along the b axis. The structure is further stabilized by C—H⋯π interactions.