Triterpene Derivatives as Potential Inhibitors of the RBD Spike Protein from SARS-CoV-2: An In Silico Approach.

The appearance of a new coronavirus, SARS-CoV-2, in 2019 kicked off an international public health emergency. Although rapid progress in vaccination has reduced the number of deaths, the development of alternative treatments to overcome the disease is still necessary. It is known that the infection begins with the interaction of the spike glycoprotein (at the virus surface) and the angiotensin-converting enzyme 2 cell receptor (ACE2). Therefore, a straightforward solution for promoting virus inhibition seems to be the search for molecules capable of abolishing such attachment. In this work, we tested 18 triterpene derivatives as potential inhibitors of SARS-CoV-2 against the receptor-binding domain (RBD) of the spike protein by means of molecular docking and molecular dynamics simulations, modeling the RBD S1 subunit from the X-ray structure of the RBD-ACE2 complex (PDB ID: 6M0J). Molecular docking revealed that at least three triterpene derivatives of each type (i.e., oleanolic, moronic and ursolic) present similar interaction energies as the reference molecule, i.e., glycyrrhizic acid. Molecular dynamics suggest that two compounds from oleanolic and ursolic acid, OA5 and UA2, can induce conformational changes capable of disrupting the RBD-ACE2 interaction. Finally, physicochemical and pharmacokinetic properties simulations revealed favorable biological activity as antivirals.

Synthesis, In Vitro, and In Silico Analysis of the Antioxidative Activity of Dapsone Imine Derivatives.

Dapsone (DDS) is an antibacterial drug with well-known antioxidant properties. However, the antioxidant behavior of its derivatives has not been well explored. In the present work, the antioxidant activity of 10 dapsone derivatives 4-substituted was determined by an evaluation in two in vitro models (DPPH radical scavenging assay and ferric reducing antioxidant power). These imine derivatives 1-10 were obtained through condensation between DDS and the corresponding aromatic aldehydes 4-substuited. Three derivatives presented better results than DDS in the determination of DPPH (2, 9, and 10). Likewise, we have three compounds with better reducing activity than dapsone (4, 9, and 10). In order to be more insight, the redox process, a conceptual DFT analysis was carried out. Molecular descriptors such as electronic distribution, the total charge accepting/donating capacity (I/A), and the partial charge accepting/donating capacity (ω+/ω-) were calculated to analyze the relative donor-acceptor capacity through employing a donor acceptor map (DAM). The DFT calculation allowed us to establish a relationship between GAPHOMO-LUMO and DAM with the observed antioxidant effects. According to the results, we concluded that compounds 2 and 3 have the lowest Ra values, representing a good antioxidant behavior observed experimentally in DPPH radical capturing. On the other hand, derivatives 4, 9, and 10 display the best reducing capacity activity with the highest ω- and Rd values. Consequently, we propose these compounds as the best antireductants in our DDS imine derivative series.

Replacement of oxidizable residues predicted by QM-MM simulation of a fungal laccase generates variants with higher operational stability.

In this work, we sought to obtain a more stable laccase with higher operational stability for the oxidation of phenols. During this reaction, phenoxy free radicals are produced that gradually inactivate the enzyme; the inactivation rate depends on the phenol chemical nature. In order to predict residues prone to oxidize within the active site, we simulated activated states of the catalytic region of a fungal laccase using QM-MM tools (Quantum Mechanics-Molecular Mechanics). After simulating the electron distribution in both the basal and activated state (plus or minus one electron) of several conformations of Coriolopsis gallica laccase, residues that could be susceptible to oxidation were identified, according to the values of spin density obtained from calculations. Three targets were selected (F357, F413, and F475) to be replaced by site-directed mutagenesis with less oxidizable residues such as leucine, alanine, and isoleucine. The resulting variants displayed a higher specific activity (from 1.5-to 4-fold) than the parental enzyme. Catalyst depletion during phenol oxidation was 2.5-fold lower for the variants, reflecting a higher operational stability.

Recombinant expression of a laccase from Coriolopsis gallica in Pichia pastoris using a modified α-factor preproleader.

In this work we communicate the heterologous expression of a laccase from Coriolopsis gallica in Pichia pastoris. This enzyme has been reported to efficiently degrade a variety of pollutants such as industrial dyes. The expression strategy included using a previously reported modified α-factor preproleader for enhanced secretion and pAOX1, a methanol-responsive promoter. Methanol concentration, copper salts concentration and temperature were varied in order to enhance laccase expression in this heterologous system. A volumetric activity of 250 U/L was achieved after 12-day culture in Fernbach flasks. The protein was recovered from the supernatant and purified, obtaining a preparation with 90% electrophoretic purity. The catalytic constants of the recombinant enzyme are almost identical to the fungal enzyme, thus rendering this system a useful tool for protein engineering of laccase from C. gallica.

Iron, cadmium, and chromium in seagrass (Thalassia testudinum) from a coastal nature reserve in karstic Yucatán.

The management of protected areas in karstic regions is a challenge because flooded cave systems form there and provide underground hydrological conducts that may link different zones. As a consequence, affectations to the protected areas can possibly occur as a consequence of human activities in remote areas and may therefore pass undetected. Thus, the monitoring of possible contaminants in these regions is becoming imperative. In this work, we analyze the concentration of essential (iron) and non-essential metals (cadmium and chromium) in the seagrass Thalassia testudinum that grows in Yalahau Lagoon, located in a near-to-pristine protected area of the Yucatán Peninsula, close to the rapidly developing touristic belt of the Mexican Caribbean. Salinity and silicate patterns show that Yalahau is an evaporation lagoon, where groundwater discharge is important. High iron (> 400 µg/g), cadmium (>4 µg/g), and chromium (≈ 1 µg/g) concentrations were found in the area of highest groundwater input of the lagoon. High levels (5.1 µg/g) were also found near the town dump. In the rest of the sampling sites, metal concentrations remained near to background levels as estimated from other works. Temporal changes of concentrations in the seagrass tissues show also a local input and an input from the groundwater that could provoke an environmental problem in the Yalahau Lagoon in the near future.

Synthesis and characterization of novel dendrons bearing amino-nitro-substituted azobenzene units and oligo(ethylene glycol) spacers: thermal, optical properties, Langmuir blodgett films and liquid-crystalline behaviour.

In this work, we report the synthesis and characterization of a novel series of first and second generation Fréchet type dendrons bearing amino-nitro substituted azobenzene units and tetra(ethylene glycol) spacers. These compounds were fully characterized by FTIR, 1H and 13C-NMR spectroscopies, and their molecular weights were determined by MALDI-TOF-MS. The thermal properties of the obtained dendrons were studied by TGA and DSC and their optical properties by absorption spectroscopy in solution and cast film. Molecular calculations were performed in order to determine the optimized geometries of these molecules in different environments. Besides, Langmuir and Langmuir Blodgett films were prepared with the first generation dendrons that were shown to be amphiphilic. Finally, some of the dendrons showed a liquid crystalline behaviour, which was studied by light polarized microscopy as a function of the temperature in order to determine the transition temperatures and the structure of the mesophase.