Yean Kee Lee

Benzimidazole derivatives as potential dual inhibitors for PARP-1 and DHODH.

Poly (ADP-ribose) polymerases (PARPs) play diverse roles in various cellular processes that involve DNA repair and programmed cell death. Amongst these polymerases is PARP-1 which is the key DNA damage-sensing enzyme that acts as an initiator for the DNA repair mechanism. Dihydroorotate dehydrogenase (DHODH) is an enzyme in the pyrimidine biosynthetic pathway which is an important target for anti-hyperproliferative and anti-inflammatory drug design. Since these enzymes share a common role in the DNA replication and repair mechanisms, it may be beneficial to target both PARP-1 and DHODH in attempts to design new anti-cancer agents. Benzimidazole derivatives have shown a wide variety of pharmacological activities including PARP and DHODH inhibition. We hereby report the design, synthesis and bioactivities of a series of benzimidazole derivatives as inhibitors of both the PARP-1 and DHODH enzymes.

Synthesis, characterization, and theoretical study of an acrylamide-based magnetic molecularly imprinted polymer for the recognition of sulfonamide drugs

Abstract In this work, a magnetic molecularly imprinted polymer (MION-MIP) was prepared for the recognition and extraction of sulfadiazine (SDZ). The acrylamide-based MIP was imprinted directly onto the surface of 3-(trimethoxysilyl)propyl methacrylate-modified magnetic iron oxide nanoparticles. The synthesized MION-MIP with a diameter about 100 nm possesses fast adsorption kinetics and high adsorption capacity. The results also indicated that a higher maximum adsorption capacity (775 μg g-1) was achieved by the synthesized MION-MIP. The Langmuir adsorption isotherm model was found to describe well the equilibrium adsorption data. The results from the competitive binding experiment showed that MION-MIP was not only selective toward SDZ but the adsorption of sulfamerazine was also dramatically high. SDZ and sulfamerazine have an almost similar substructure where these two compounds were only differentiated by one methyl group. To explain this result, a computational study was carried out. From a different level of calculation with semiempirical (PM3), Hartree-Fock (HF), and density functional theory (DFT) calculation, SDZ and sulfamerazine showed similar interaction energy and interaction mechanism with the acrylamide monomer. Therefore, both SDZ and sulfamerazine could have the same binding property with the MION-MIP.

Quantitative LC/MS/MS analysis of acetaminophen–cysteine adducts (APAP–CYS) and its application in acetaminophen overdose patients

A more sensitive approach by liquid chromatography–tandem mass spectrometry (LC/MS/MS) method using the AB Sciex QTRAP 5500 was developed and validated for the detection and quantification of acetaminophen–cysteine adducts (APAP–CYS) in human plasma. Chromatographic separation was achieved using a Protecol P C18 column (2.1 mm i.d. × 100 mm, 3 microns). The mobile phase consists of A: 2 mM ammonium formate in water (0.2% formic acid) and B: 2 mM ammonium formate in acetonitrile (0.2% formic acid). The analysis was performed using positive and negative ion electrospray ionization (ESI) in multiple reaction monitoring mode (MRM) with a total run time of 7 min per assay. The MS/MS ion transitions monitored were m/z 271 → 140 for APAP–CYS (positive mode) and m/z 154 → 111 for acetaminophen-D4 (negative mode). The newly developed method showed good linearity in the range of 1.0 to 100 ng mL−1. Inter and intra batch precision and accuracy of the method ranged from 0.28 to 5.30% and 87.0 to 113% respectively. LOD was 0.5 ng mL−1 and LLOQ was 1.0 ng mL−1. Analytes were extracted from plasma samples by simple protein precipitation using acetonitrile. The method was successfully applied in a preliminary clinical study to determine APAP–CYS concentration from 46 acetaminophen overdose patients treated at outpatient clinic in the University Malaya Medical Centre.

Comparative proteomics reveals that YK51, a 4-Hydroxypandurantin-A analogue, downregulates the expression of proteins associated with dengue virus infection

Dengue is endemic throughout tropical and subtropical regions of the world. Currently, there is no clinically approved therapeutic drug available for this acute viral infection. Although the first dengue vaccine Dengvaxia has been approved for use in certain countries, it is limited to those without a previous dengue infection while the safety and efficacy of the vaccine in those elderly and younger children still need to be identified. Therefore, it is becoming increasingly important to develop therapeutics/drugs to combat dengue virus (DENV) infection. YK51 is a synthetic analogue of 4-Hydroxypandurantin A (a compound found in the crude extract of the rhizomes of Boesenbergia rotunda) that has been extensively studied by our research group. It has been shown to possess outstanding antiviral activity due to its inhibitory activity against NS2B/NS3 DENV2 protease. However, it is not known how YK51 affects the proteome of DENV infected cells. Therefore, we performed a comparative proteomics analysis to identify changes in protein expression in DENV infected HepG2 cells treated with YK51. Classical two-dimensional gel electrophoresis followed by protein identification using tandem mass spectrometry was employed in this study. Thirty proteins were found to be down-regulated with YK51 treatment. In silico analysis predicted that the down-regulation of eight of these proteins may inhibit viral infection. Our results suggested that apart from inhibiting the NS2B/NS3 DENV2 protease, YK51 may also be causing the down-regulation of a number of proteins that may be responsible in, and/or essential to virus infection. However, functional characterization of these proteins will be necessary before we can conclusively determine their roles in DENV infection.

Contrasting sirtuin and poly(ADP-ribose)polymerase activities of selected 2,4,6-trisubstituted benzimidazoles

Both sirtuin and poly(ADP‐ribose)polymerase (PARP) family of enzymes utilize NAD+ as co‐substrate. Inhibitors of sirtuins and PARPs are important tools in drug discovery as they are reported to be linked to multiple diseases such as cancer. New potent sirtuin inhibitors (2,4,6‐trisubstituted benzimidazole) were discovered from reported PARP inhibitor scaffold. Interestingly, the synthesized compounds have contrasting sirtuin and PARP‐1 inhibitory activities. We showed that modification on benzimidazoles may alter their selectivity toward sirtuin or PARP‐1 enzymes. This offers an opportunity for further discovery and development of new promising sirtuin inhibitors. Molecular docking studies were carried out to aid the rationalization of these observations. Preliminary antiproliferative studies of selected compounds against nasopharyngeal cancer cells also showed relatively promising results.

Application of chalcone-based dithiocarbamate derivative incorporated sol-gel for the removal of Hg (II) ion from water

This study demonstrated the application of chalcone-based dithiocarbamate derivative as metal capturing ligand for the removal of mercury ion (Hg2+) in water. Chalcones are a group of naturally occurring compounds which can be obtained from fruits, vegetables, plants, and spice. In this study, chalcone was first chemically modified to produce dithiocarbamate derivative (ODPPNE). Chalcone and ODPPNE were then incorporated into sol–gel to produce SG-C and SG-ODPPNE, respectively, as adsorbents. The result from the adsorption study showed that with the presence of dithiocarbamate functional group, SG-ODPPNE exhibited the highest selectivity toward the adsorption of Hg2+ with lesser response to Cr3+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+. The adsorption of Hg2+ by SG-ODPPNE was found to be adsorbent size, adsorbent dosage, contact time, the initial concentration of sorbate and pH dependent. The obtained experimental data were also analyzed using Freundlich and Langmuir adsorption models. The results showed that the adsorption data were well-fitted to Langmuir isotherm, and the monolayer absorption capacity was found to be 13.5 mg/g. In the absorption kinetic study, the data was analyzed using pseudo-first-order, pseudo-second-order kinetic model, and intraparticle diffusion model. The obtained data were well-fitted to pseudo-second order model. According to intraparticle diffusion model, the adsorption process of Hg2+ by SG-ODPPNE involves film diffusion, intraparticle diffusion, and equilibrium stages.Graphical Abstract

Transition State Study of Cyclization Step in Peptide Catalyzed Flavanone Synthesis

Our strategy is to use the computational method through the transition state study and molecular design the appropriate substrate in control the enantioselectivity. The mechanistic study employing quantum mechanical calculations has been studied for the peptide catalyzed flavanone synthesis. The pathways using synchronous transit method with local density approximations with PWC functional for the fragment in the cyclization step were obtained. The reactions between substrate and peptide in both axial and equatorial attacks of hydroxyl which leads to different enantiomers were investigated. The calculated energies for both systems were comparable with the barrier difference of 1.42 kcal/mol.