Yip-Foo Win

Heterocyclic benzothiazole-based liquid crystals: synthesis and mesomorphic properties

Two homologous series of 2-(4-alkanoyloxybenzylidenamino)benzothiazoles and 2-(2-hydroxy-4-alkanoyloxybenzylidenamino)benzothiazoles were synthesised and characterised. Their molecular structures differed wherein the latter comprised a lateral hydroxyl group, unlike the former. Spectroscopic techniques such as FT-IR, 1H & 13C NMR and mass spectrometry together with elemental analysis were employed to elucidate the molecular structures. The transition temperatures and their mesophases were determined by differential scanning calorimetry, optical polarising microscopy and X-ray diffraction techniques. Members with decanoyloxy till hexadecanoloxy chain in the series without the lateral hydroxyl group each exhibited a smectic A phase, while those in the series with the lateral hydroxyl group were non-mesogenic. The mesomorphic properties of the present series were compared with other structurally related series to establish the chemical structure–mesomorphic properties relationship.

Synthesis and Mesomorphic Properties of 2-(4-Alkyloxyphenyl)benzothiazoles

A homologous series of 2-(4-alkyloxyphenyl)benzothiazoles with an even number of carbons in the terminal alkoxyl chain was synthesized and characterized. The structure of the compounds was postulated using elemental analyses, FT-IR, NMR, and mass spectrometry techniques. Their liquid crystalline properties have been investigated by optical polarizing microscopy, DSC, and X-ray diffraction (XRD) techniques. Whilst the n-octyloxy to n-hexadecyloxy derivatives exhibited a monotropic smectic A phase, the n-ethoxy to n-hexyloxy and the n-octadecyloxy derivatives were not mesogenic. The mesomorphic properties of the present series were compared with other structurally related series to establish the chemical structure-mesomorphic properties relationship.

Synthesis of New Schiff Base: 4-[(Pyridin-3-ylmethylene)- amino]phenyldodecanoate

A new Schiff base 4-[(pyridin-3-ylmethylene)amino]phenyldodecanoate was synthesized via Steglich esterification. IR, 1H NMR, 13C NMR and MS spectroscopic data are presented.

Polymeric seven-coordinated organotin(IV) complexes derived from 5-amino-2-chlorobenzoic acid and in vitro anti-cancer studies

Cancer cases are alarmingly increasing worldwide, and newer chemotherapeutic agents are needed. Recent analogs of cisplatin (carboplatin, lobaplatin, nedaplatin and oxaliplatin) and their marketing as advanced chemotherapeutic drugs have furthered the interest in metal-based anti-cancer drugs. In the current study, two new polymeric organotin(IV) carboxylate complexes (1 and 2) have been synthesized and characterized. Spectroscopic studies showed that coordination took place via carboxylates. Furthermore, X-ray crystallographic study on 1 indicated that it possesses a monomeric structure and exists in polymeric formation due to additional Sn–N coordination, assigning seven coordinations to each metal ion. Both the complexes were tested against three cancerous (human colon cancer, HCT 116; breast cancer, MCF-7; and leukemia, K562) and one non-cancerous (3T3-L1) cell lines. Complex 1 showed exceptional cytotoxicity against cancerous cell lines (IC50 = 1.0 μM for HCT 116; 258.7 nM for MCF-7; and 46.7 nM K562) and remained comparatively non-toxic against normal cells (IC50 = 37.0 μM). This shows that both complexes have selective cytotoxicity against cancer cells. Graphical Abstract

Phase transition behaviours of calamitic liquid crystals comprising phenylbenzothiazole core

A series of new calamitic liquid crystals 2-[4-(4-alkyloxybenzoyloxy)-phenyl]benzothiazoles comprising a benzothiazole core, terminal alkyl chain and an ester linkage were synthesised and characterised. This series consists of 13 members, wherein the members differ by the length of alkyloxy chain (C n H2n+1O−, where n = 2–10, 12, 14, 16, 18). Their mesomorphic properties were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. Enantiotropic nematic phase was present throughout the series, i.e. from the lowest member (n = 2) until the highest member (n = 18) of the series. The smectic A phase emerged from the nonyloxy derivative onwards.

Benzofuranyl Esters: Synthesis, Crystal Structure Determination, Antimicrobial and Antioxidant Activities

A series of five new 2‐(1‐benzofuran‐2‐yl)‐2‐oxoethyl 4-(un/substituted)benzoates 4(a–e), with the general formula of C8H5O(C=O)CH2O(C=O)C6H4X, X = H, Cl, CH3, OCH3 or NO2, was synthesized in high purity and good yield under mild conditions. The synthesized products 4(a–e) were characterized by FTIR, 1H-, 13C- and 1H-13C HMQC NMR spectroscopic analysis and their 3D structures were confirmed by single-crystal X-ray diffraction studies. These compounds were screened for their antimicrobial and antioxidant activities. The tested compounds showed antimicrobial ability in the order of 4b < 4a < 4c < 4d < 4e and the highest potency with minimum inhibition concentration (MIC) value of 125 µg/mL was observed for 4e. The results of antioxidant activities revealed the highest activity for compound 4e (32.62% ± 1.34%) in diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, 4d (31.01% ± 4.35%) in ferric reducing antioxidant power (FRAP) assay and 4a (27.11% ± 1.06%) in metal chelating (MC) activity.

Preliminary in vitro cytotoxic assay of human liver carcinoma cells (HepG2) of organotin(IV) complexes: Synthesis and characterization of organotin(IV) complexes of 2,4-dinitrobenzoic and 3,5-dinitrobenzoic acids

A total of five organotin(IV) carboxylate complexes was successfully synthesized and characterized quantitatively and qualitatively. Results of the infrared spectroscopy of the parent acids and complexes showed that the coordination took place via oxygen atoms from the carboxylate group. From the preliminary in vitro cytotoxic assay study, triorganotin(IV) complexes (2 and 5) were found to exhibit better activity as compared to diorganotin(IV) complexes (1, 3 and 4) but lower activity as compared to the reference drug. In addition, within the diorganotin(IV) complexes, monomeric type (3) exhibited a slightly better activity as compared to the organodistannoxane dimer types (1 and 4). Keywords: Preliminary in vitro cytotoxic assay, organotin(IV) complexes, comparison study

(2-Amino-3-nitro­benzoato-κO)triphenyl­tin(IV)

The asymmetric unit of the title compound, [Sn(C6H5)3(C7H5N2O4)], consists of two independent molecules. In each molecule, the four-coordinated SnIV atom exists in a distorted tetrahedral geometry and two intramolecular N—H⋯O hydrogen bonds with S(6) ring motifs are present. In one molecule, the benzene ring of the 2-amino-3-nitrobenzoate ligand makes dihedral angles of 42.74 (11), 89.66 (13) and 53.04 (10)° with the three phenyl rings. The corresponding dihedral angles for the other molecule are 6.29 (11), 66.55 (11) and 62.33 (10)°. In the crystal, a weak intermolecular C—H⋯π interaction and a π–π stacking interaction with a centroid–centroid distance of 3.5877 (12) Å are observed.

Synthesis, structural and antioxidant studies of some novel N-ethyl phthalimide esters.

A series of N-ethyl phthalimide esters 4(a-n) were synthesized and characterized by spectroscopic studies. Further, the molecular structure of majority of compounds were analysed by single crystal X-ray diffraction studies. The X-ray analysis revealed the importance of substituents on the crystal stability and molecular packing. All the synthesized compounds were tested for in vitro antioxidant activity by DPPH radical scavenging, FRAP and CUPRAC methods. Few of them have shown good antioxidant activity.

Synthesis and mesomorphic behaviours of a homologous series of 2-(4-alkyloxybenzylidenamino)benzothiazoles

The synthesis and characterisation of a series of new rod-shaped liquid crystal (LC), 2-(4-alkyloxybenzylidenamino)benzothiazoles possessing even number of carbon atoms at the alkyloxy chain (CnH2n + 1O-, n = 2, 4, 6, 8, 10, 12, 14, 16, 18) are reported. The molecular structures of title compounds were elucidated using FTIR and nuclear magnetic resonance spectroscopic techniques. The phase behaviour of these new compounds was characterised and studied by differential scanning calorimetry and polarising optical microscopy. Lower members (n = 2, 4 and 6) did not exhibit mesophase. Octyloxy derivative was monotropic LC. Enantiotropic smectic A phase was observed from n-decyloxy derivatives onward to the last homologous synthesised.