Yasodha Sivasothy

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.

A potent alpha-glucosidase inhibitor from Myristica cinnamomea King

A dimeric acylphenol and a potent α-glucosidase inhibitor, giganteone D (IC50 5.05μM), was isolated and characterized from the bark of Myristica cinnamomea King. The bark also yielded an acylphenol with an unprecedented skeleton for which the name cinnamomeone A (IC50 358.80μM) was proposed. Their structures were established by means of NMR and MS spectrometric analyses. The Lineweaver-Burk plot of giganteone D indicated that it was a mixed-type inhibitor. This is the first report on the α-glucosidase inhibiting potential of acylphenols.

Chemical Composition and Antibacterial Activities of Essential Oils from Zingiber spectabile Griff

The essential oils of the leaves and rhizomes of Zingiber spectabile Griff. were analyzed by capillary gas chromatography (GC) and GC–mass spectrometry (GC–MS) following the isolation by hydrodistillation. In total, 80 compounds were identified in its leaf and rhizome oils. Both oils were sesquiterpenic in nature but with distinctly different odors. The most abundant components in the leaf oil were β-caryophyllene (21.3%) and β-elemene (12.5%), whereas the rhizomes yielded an oil rich in zerumbone (59.1%). The antibacterial activities of both oils against multidrug-resistant strains and food-borne pathogens were evaluated by the disc diffusion assay and by determining their minimum inhibitory concentration (MIC) values. The leaf oil was inactive against all tested microorganisms, whereas the rhizome oil exhibited weak activity against Escherichia coli, Salmonella enteritidis, Salmonella typhi, Salmonella typhimurium, Shigella flexneri, Klebsiella pneumoniae, Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA).

Pahangensin A and B, two new antibacterial diterpenes from the rhizomes of Alpinia pahangensis Ridley

The rhizomes of Alpinia pahangensis Ridley yielded a new bis-labdanic diterpene for which the name pahangensin A (1) was proposed along with a new labdane diterpene, pahangensin B (2). Their structures were elucidated by spectroscopic methods including, 1D and 2D NMR techniques and LCMS-IT-TOF analysis. Pahangensin A (1) was found to be an antibacterial agent against Staphylococcus aureus, Bacillus cereus and Bacillus subtilis with MIC values less than 100 μg/mL, respectively. Pahangensin B (2) exhibited antibacterial activity (MIC <100 μg/mL) against B. cereus.

Spectaflavoside A, a new potent iron chelating dimeric flavonol glycoside from the rhizomes of Zingiber spectabile Griff

The rhizomes of Zingiber spectabile yielded a new dimeric flavonol glycoside for which the name kaempferol-3-O-(4″-O-acetyl)-α-L-rhamnopyranoside-(I-6,II-8)-kaempferol-3-O-(4″-O-acetyl)-α-L-rhamnopyranoside; spectaflavoside A (1) was proposed, along with kaempferol and its four acetylrhamnosides (2-6), demethoxycurcumin (7) and curcumin (8). The structure of spectaflavoside A was elucidated by spectroscopic methods including, 1D and 2D NMR techniques. This is the first report on the occurrence of a dimeric flavonol glycoside in the Zingiberaceae and the second in nature. Spectaflavoside A was found to be a potent iron chelating agent.

Hyaluronidase Inhibitory Activity of Pentacylic Triterpenoids from Prismatomeris tetrandra (Roxb.) K. Schum: Isolation, Synthesis and QSAR Study

The mammalian hyaluronidase degrades hyaluronic acid by the cleavage of the β-1,4-glycosidic bond furnishing a tetrasaccharide molecule as the main product which is a highly angiogenic and potent inducer of inflammatory cytokines. Ursolic acid 1, isolated from Prismatomeris tetrandra, was identified as having the potential to develop inhibitors of hyaluronidase. A series of ursolic acid analogues were either synthesized via structure modification of ursolic acid 1 or commercially obtained. The evaluation of the inhibitory activity of these compounds on the hyaluronidase enzyme was conducted. Several structural, topological and quantum chemical descriptors for these compounds were calculated using semi empirical quantum chemical methods. A quantitative structure activity relationship study (QSAR) was performed to correlate these descriptors with the hyaluronidase inhibitory activity. The statistical characteristics provided by the best multi linear model (BML) (R2 = 0.9717, R2cv = 0.9506) indicated satisfactory stability and predictive ability of the developed model. The in silico molecular docking study which was used to determine the binding interactions revealed that the ursolic acid analog 22 had a strong affinity towards human hyaluronidase.

Natural cholinesterase inhibitors from Myristica cinnamomea King.

A new acylphenol, malabaricone E (1) together with the known malabaricones A-C (2-4), maingayones A and B (5 and 6) and maingayic acid B (7) were isolated from the ethyl acetate extract of the fruits of Myristica cinnamomea King. Their structures were determined by 1D and 2D NMR techniques and LCMS-IT-TOF analysis. Compounds 3 (1.84±0.19 and 1.76±0.21μM, respectively) and 4 (1.94±0.27 and 2.80±0.49μM, respectively) were identified as dual inhibitors, with almost equal acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes inhibiting potentials. The Lineweaver-Burk plots of compounds 3 and 4 indicated that they were mixed-mode inhibitors. Based on the molecular docking studies, compounds 3 and 4 interacted with the peripheral anionic site (PAS), the catalytic triad and the oxyanion hole of the AChE. As for the BChE, while compound 3 interacted with the PAS, the catalytic triad and the oxyanion hole, compound 4 only interacted with the catalytic triad and the oxyanion hole.

Acylphenols and dimeric acylphenols from Myristica maxima Warb.

Giganteone E (1), a new dimeric acylphenol was isolated as a minor constituent from the bark of Myristica maxima Warb. The structure of 1 was established on the basis of 1D and 2D NMR techniques and LCMS-IT-TOF analysis. Malabaricones A-C (2-4), giganteones A and C (5 and 6), maingayones A and B (7 and 8), maingayic acid B (9) and β-sitosteryl oleate (10) were also characterized in this plant for the first time. Compound 10 was identified for the first time in the Myristicaceae. Compounds 2 and 5 were active against human prostate cancer cell-lines, thus making this the first report on the prostate cancer inhibiting potential of acylphenols and dimeric acylphenols. Compounds 1, 4, 5, 7 and 8 exhibited potent DPPH free radical scavenging activity. This is the first report on their free radical scavenging capacity.

Ultraviolet-visible study on acid-base equilibria of aporphine alkaloids with antiplasmodial and antioxidant activities from Alseodaphne corneri and Dehaasia longipedicellata

The UV-vis spectra of isocorydine 1, norisocorydine 2 and boldine 3 were studied in 2% v/v acetonitrile, at constant ionic strength (0.1 M NaCl, 35 degree Celsius). The pKa values of isocorydine 1 and norisocorydine 2 were 11.75 and 12.07, respectively. Boldine 3 gave a pKa value of 9.16 and 10.44. All of the alkaloids 1–3 were stable at physiological pH; thereby all of them will not ionize, thus permitting the basic nitrogen to be protonated and accumulated within the acidic food vacuole of Plasmodium via pH trapping. Subsequently, acidic food vacuoles that have been neutralized by alkaloids would result in enhancement of the antiplasmodial activity. The alkaloids showed antiplasmodial activity against Plasmodium falciparum and antioxidant activities; DPPH radical scavenging, metal chelating and ferric reducing power. The antioxidant properties of the alkaloids under investigation revealed that in addition to the antiplasmodial activity, the alkaloids can also prevent oxidative damage. It can be prevented by binding free heme and neutralizing the electrons produced during the Plasmodium falciparum mediated haemoglobin destruction in the host. Slightly basic properties of the aforementioned alkaloids, along with their antioxidant activities, are advantageous in improving the suppression of malaria infection that cause less damage to the host.

Essential Oil Composition and Antimicrobial Activities of Two Closely Related Species, Alpinia mutica Roxb. and Alpinia latilabris Ridl., from Peninsular Malaysia

The essential oils obtained by hydrodistillation of the unripe and ripe fruits of Alpinia mutica Roxb. and Alpinia latilabris Ridl. were analysed by capillary GC and GC-MS. The oils were principally monoterpenic in nature. The unripe and ripe fruit oils of A. mutica were characterized by camphor (21.0% and 15.8%), camphene (16.6% and 10.2%), β-pinene (8.6% and 13.5%), and trans,trans-farnesol (8.0% and 11.2%), respectively. The oils of the unripe and ripe fruits were moderately active against Staphylococcus aureus, Bacillus subtilis, Trichophyton mentagrophytes, and Trichophyton rubrum. 1,8-Cineole (34.2% and 35.9%) and β-pinene (20.2% and 19.0%) were the two most abundant components in the unripe and ripe fruit oils of A. latilabris. The oil of the unripe fruits elicits moderate activity against Staphylococcus aureus and Trichophyton mentagrophytes while Candida glabrata was moderately sensitive to the oil of the ripe fruits.