Sulfated Polysaccharide, Curdlan Sulfate, Efficiently Prevents Entry/Fusion and Restricts Antibody-Dependent Enhancement of Dengue Virus Infection In Vitro: A Possible Candidate for Clinical Application

10.1371/journal.pntd.0002188PLoS Neglected Tropical Diseases74

Direct esterification of allylic C(sp3)–H via iron nanoparticle–loaded kaolin-catalyzed cross dehydrogenative coupling

ABSTRACTIron is the most abundant transition metal on Earth. In this study, we have demonstrated an iron nanoparticle–loaded kaolin-catalyzed cross dehydrogenative coupling (CDC) reaction via C(sp3)–H activation. We use CDC of carboxylic acids with cyclohexenes to discuss various reaction parameters such as the amount of catalyst, oxidant, reaction temperature, and time. Under optimized reaction condition, the corresponding allylic ester was obtained with good yield of (85%). Screening of substituted benzoic acids and cyclic and acyclic olefins shows broad catalytic activities. Notably, the catalyst can be easily separated from the reaction mixture via simple centrifugation and remains active over five cycles of reuse

Chemical structure of CRDS and antiviral activity based on DENV-2 MTT assay using LLC-MK2 cells.

<p>Structure of CRDS (A) and dose-dependent inhibition of DENV-2 infection by CRDS by MTT assay (B).</p

Proposed binding model of CRDS to DENV envelope protein obtained by Induced fit docking.

<p>The coordinates of the DENV E protein were obtained from PDB from the crystal structure 1OKE <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002188#pntd.0002188-Modis1" target="_blank">[13]</a>. Detailed information is described in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002188#s2" target="_blank">Materials and Methods</a>.</p

Efficient inhibitory effect of CRDS on DENV replication in monocytic HL-60 cells.

<p>Anti-DENV-2 was monitored at 100 µg/mL of CRDS 4 days after infection in HL-60 cells.</p

Effect of CRDS on DENV-2 infection in DC-SIGN-expressing cells.

<p>The effect of CRDS was evaluated on DENV infection in DC-SIGN expressing cells. Raji-DC-SIGN cells were infected with large amount of DENV (1000 pfu) in the presence of CRDS. The cultures were analyzed for DENV infection by FACS assays 4 days later.</p

LigPlot⁺ representation of the hydrophobic interactions between CRDS and the residues of the binding pocket.

<p>The hydrophobic contacts are represented by dotted lines. The LigPlot⁺<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002188#pntd.0002188-Laskowski1" target="_blank">[49]</a> was used to map the interactions.</p

Effect of CRDS on low pH-induced fusion of DENV-2 infected C6/36 cells.

<p>The cells were incubated with DENV at 4°C for 1.5 h during viral adsorption in the presence of 100 µg/mL of either CRDS or heparin, followed by a temperature shift to 28°C, and cultured for 4 days to monitor virus-induced cell fusion (A). In the experiment shown in B, the compound was added at the time of temperature shift to 28°C, after viral attachment.</p

Antiviral activity of CRDS on the four dengue virus serotypes.

<p>Antiviral activity of CRDS on the four dengue virus serotypes.</p

CRDS inhibits both attachment as well as an early post-attachment step of entry.

<p>Time of addition experiments were performed to identify the step at which CRDS exerts its effect (A) and efficacy of inhibitors during attachment and post-attachment (B). Studies were performed using the LLC-MK2 cells as described in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002188#s2" target="_blank">Materials and Methods</a> in detail.</p