Antiviral actions of flavanoid-derived compounds on dengue virus type-2

Dengue viruses, mosquito-borne members of the Flaviviridae family, are the causative agents of dengue fever and its associated complications, dengue haemorrhagic fever and dengue shock syndrome. To date, more than 2.5 billion people in over 100 countries are at risk of infection, and approximately 20 million infections were reported annually. There is currently no treatment or vaccine available for dengue infection. This study employed a whole-cell organism model or in vitro methods to study the inhibitory property of the flavanoid-derived compounds against DENV2 activity. Results showed that at concentration not exceeding the maximum non-toxic dose (MNTD), these compounds completely prevented DENV2 infection in HepG2 cells as indicated by the absence of cytophatic effects. The in vitro antiviral activity assessed in HepG2 cells employing virus inhibition assay showed high inhibitory activity in a dose dependent manner. At concentration below MNTD, compounds exhibited inhibitory activity against DENV2 with a range of potency strengths of 72% to 100%. The plaque forming unit per ml (pfu/ml) was reduced prominently with a maximum reduction of 98% when the infected HepG2 cells were treated with the highest non-toxic dose of compounds. The highly potent activity of the compounds against DENV2 infection strongly suggests their potential as a lead antiviral agent for dengue

Biosynthesis and Biomimetic Synthesis of Flavonoid Diels-Alder Natural Products

This chapter describes the biosynthesis and biomimetic synthesis of naturally occurring flavonoid Diels‐Alder adducts found either from the family Moraceae or Zingiberaceae. The main topics addressed are biosynthetic studies by employing Morus alba L. cell cultures through feeding experiments of various exogenous substrates and putative precursors, as well as a various biomimetic approach for the chemical syntheses of flavonoid Diels‐Alder natural products

Screening of selected Zingiberaceae extracts for dengue-2 virus protease inhibitory activities

The crude extracts and the methanol and hexane partitioned fractions from the rhizomes of six Zingiberaceae comprising five Curcumas and one Zingiber were screened for dengue-2 (Den2) virus NS2B?NS3 protease inhibition. The percentage inhibition of Den2 virus NS2B?NS3 protease cleavage of the substrate showed linear dose-dependent increment for all the samples tested. The crude extracts were less potent than the best of the partitioned fractions. For all three concentrations studied, the methanol fractions of the extracts of Curcuma longa (L.) (CL), Zingiber zerumbet Smith (ZZ) and Curcuma rubescen Roxb. (CR) were much more inhibiting than the corresponding hexane fractions but the converse was true for Curcuma aeroginosa Roxb. (CA). However, the inhibiting activities of the two partitioned fractions of the extracts of Curcuma mangga Roxb. (CM) and Curcuma xanthorhiza Roxb. (CX) were found to be similar. The CL methanol fraction exhibited the strongest inhibitory activity (91.3±3.1%, 300 ppm), followed closely by methanol fraction of ZZ (89.0±1.7%, 300 ppm). The results show that the methanol fractions of CL and ZZ, and both the methanol and hexane fractions of CM were most potent against Den2 virus NS2B?NS3 protease activity and may provide potential leads towards the development of anti-viral agents

Molecular docking studies of selected medicinal drugs as dengue virus-2 protease inhibitors

Dengue is a potentially deadly disease with no effective drug. An in silico molecular docking was performed using Autodock 4.2.6 to investigate the molecular interactions between protease inhibitors, comprising antibiotic derivatives namely doxycycline (3), rolitetracycline (5) and a non-steroidal anti-inflammatory drug (NSAID), meclofenamic acid (4), against the NS2B-NS3 protease from dengue virus-2 (DENV-2). The non-competitive inhibitor (3) showed lower binding energy (-5.15 kcal/mol) than the predicted competitive inhibitors 4 and 5 (-3.64 and -3.21 kcal/mol, respectively). Structural analyses showed compound 3 that bound to a specific allosteric site, interacted with Lys74, a significant amino acid residue bonded to one of the catalytic triad, Asp75. Compounds 4 and 5 showed direct binding with two of the catalytic triad, His51 and Ser135, hence, predicted to be competitive inhibitors

The effects of placement and geometry on thermo-pneumatic pumping on centrifugal microfluidic compact disc (CD) platforms

Thermo-pneumatic pumping (TPP) is used to pump fluids on a microfluidic compact disc (CD) to the center of the CD. The expansion of air during heating drives the fluid transfer during TPP. It is easy to fabricate the TPP air chamber and adjoining channel since there are no moving components in their structure and that the thermal energy is supplied to the pump through localized heating equipment. This allows the pumping process even while the disc is rotating. In this report, by changing the shape and placement of the air chamber, we demonstrate that the experimental behavior of the TPP process can be manipulated by the altering heating rate of the air chamber. The placement and geometry of the air expansion chambers affect the rate of transfer during the TPP process. These modifications allow for the customization of the TPP and for a better incorporation onto the microfluidic CD platform, enabling the platform to be more versatile, more complex in functions and countable to be implemented. © 2012 IEEE

Design of New Competitive Dengue Ns2b/Ns3 Protease Inhibitors—A Computational Approach

Dengue is a serious disease which has become a global health burden in the last decade. Currently, there are no approved vaccines or antiviral therapies to combat the disease. The increasing spread and severity of the dengue virus infection emphasizes the importance of drug discovery strategies that could efficiently and cost-effectively identify antiviral drug leads for development into potent drugs. To this effect, several computational approaches were applied in this work. Initially molecular docking studies of reference ligands to the DEN2 NS2B/NS3 serine protease were carried out. These reference ligands consist of reported competitive inhibitors extracted from Boesenbergia rotunda (i.e., 4-hydroxypanduratin A and panduratin A) and three other synthesized panduratin A derivative compounds (i.e., 246DA, 2446DA and 20H46DA). The design of new lead inhibitors was carried out in two stages. In the first stage, the enzyme complexed to the reference ligands was minimized and their complexation energies (i.e., sum of interaction energy and binding energy) were computed. New compounds as potential dengue inhibitors were then designed by putting various substituents successively on the benzyl ring A of the reference molecule. These substituted benzyl compounds were then computed for their enzyme-ligand complexation energies. New enzyme-ligand complexes, exhibiting the lowest complexation energies and closest to the computed energy for the reference compounds, were then chosen for the next stage manipulation and design, which involved substituting positions 4 and 5 of the benzyl ring A (positions 3 and 4 for 2446DA) with various substituents

The emission of volatile halocarbons by seaweeds and their response towards environmental changes

Volatile halocarbons can deplete the protective stratospheric ozone layer contributing to global climate change and may even affect local climate through aerosol production. These compounds are produced through anthropogenic and biogenic processes. Biogenic halocarbons may be produced as defence compounds, anti-oxidants or by-products of metabolic processes. These compounds include very short-lived halocarbons (VSLH), e.g. bromoform (CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I), diiodomethane (CH2I2). Efforts to quantify the biogenic sources of these compounds, especially those of marine origin, e.g. seaweeds, phytoplankton and seagrass meadows, are often complicated by inherent biological variability as well as spatial and temporal changes in emissions. The contribution of the coastal region and the oceans to the stratospheric load of halocarbons has been widely debated. This highlights the need to understand the factors affecting the release of these compounds from marine sources for which data for modelling purposes are generally lacking. Seaweeds are important sources of biogenic halocarbons subjected to changing environmental conditions. Huge uncertainties in the prediction of current and future global halocarbon pool exist due to the lack of spatial and temporal data input from coastal and oceanic sources. Therefore, investigating the effect of changing environmental conditions on the emission of VSLH by the seaweeds could help towards better estimations of halocarbon emissions. This is especially important in light of global changes in both climate and the environment, the expansion of seaweed cultivation industry and the interactions between halocarbon emission and their environment. In this paper, we review current knowledge of seaweed halocarbon emissions, how environmental factors affect these emissions and identify gaps in understanding. Our aim is to direct much needed research to improve understanding of the contribution of marine biogenic sources of halocarbons and their impact on the environment

Thioguanine-based DENV-2 NS2B/NS3 protease inhibitors: Virtual screening, synthesis, biological evaluation and molecular modelling

Dengue virus Type 2 (DENV-2) is predominant serotype causing major dengue epidemics. There are a number of studies carried out to find its effective antiviral, however to date, there is still no molecule either from peptide or small molecules released as a drug. The present study aims to identify small molecules inhibitor from National Cancer Institute database through virtual screening. One of the hits, D0713 (IC50 = 62 μM) bearing thioguanine scaffold was derivatised into 21 compounds and evaluated for DENV-2 NS2B/NS3 protease inhibitory activity. Compounds 18 and 21 demonstrated the most potent activity with IC50 of 0.38 μM and 16 μM, respectively. Molecular dynamics and MM/PBSA free energy of binding calculation were conducted to study the interaction mechanism of these compounds with the protease. The free energy of binding of 18 calculated by MM/PBSA is -16.10 kcal/mol compared to the known inhibitor, panduratin A (-11.27 kcal/mol), which corroborates well with the experimental observation. Results from molecular dynamics simulations also showed that both 18 and 21 bind in the active site and stabilised by the formation of hydrogen bonds with Asn174

Validation of Quantitative Structure-Activity Relationship (QSAR) Model for Photosensitizer Activity Prediction

Photodynamic therapy is a relatively new treatment method for cancer which utilizes a combination of oxygen, a photosensitizer and light to generate reactive singlet oxygen that eradicates tumors via direct cell-killing, vasculature damage and engagement of the immune system. Most of photosensitizers that are in clinical and pre-clinical assessments, or those that are already approved for clinical use, are mainly based on cyclic tetrapyrroles. In an attempt to discover new effective photosensitizers, we report the use of the quantitative structure-activity relationship (QSAR) method to develop a model that could correlate the structural features of cyclic tetrapyrrole-based compounds with their photodynamic therapy (PDT) activity. In this study, a set of 36 porphyrin derivatives was used in the model development where 24 of these compounds were in the training set and the remaining 12 compounds were in the test set. The development of the QSAR model involved the use of the multiple linear regression analysis (MLRA) method. Based on the method, r2 value, r2 (CV) value and r2 prediction value of 0.87, 0.71 and 0.70 were obtained. The QSAR model was also employed to predict the experimental compounds in an external test set. This external test set comprises 20 porphyrin-based compounds with experimental IC50 values ranging from 0.39 μM to 7.04 μM. Thus the model showed good correlative and predictive ability, with a predictive correlation coefficient (r2 prediction for external test set) of 0.52. The developed QSAR model was used to discover some compounds as new lead photosensitizers from this external test set