Design and synthesis of novel main protease inhibitors of COVID-19: quinoxalino[2,1-b]quinazolin-12-ones.

The COVID-19 pandemic represents a substantial global challenge, being a significant cause of mortality in numerous countries. Thus, it is imperative to conduct research to develop effective therapies to combat COVID-19. The primary aim of this study is to employ a two-step tandem reaction involving 2,3-dichloroquinoxaline and 2-amino-N-substituted benzamides in alkaline media/DMF at an elevated temperature to design and synthesize a series of polycyclic derivatives endowed with quinoxalino[2,1-b]quinazolin-12-one framework. Following synthesis, the newly synthesized heterocycles were evaluated for their potential as inhibitors of the main protease of SARS-CoV-2 by means of molecular docking and dynamic simulation techniques. The in silico investigation demonstrated that all tested compounds effectively establish stable binding interactions, primarily through multiple hydrogen bonding and hydrophobic interactions, at the active site of the enzyme. These findings offer crucial structural insights that can be employed in future endeavors toward designing potent inhibitors targeting the main protease (Mpro). Among the investigated compounds, the p-tolylamino-substituted quinoxalino[2,1-b]quinazolinone derivative exhibited the most promise as an inhibitor of the main protease in COVID-19. Consequently, it warrants further investigation both in vitro and in vivo to identify it as a prospective candidate for anti-SARS-CoV-2 drug development.

Understanding the effects of building block rings of π electron-rich organic photocatalysts in CO2 transformation to amino acids.

Understanding the effective factors in the performance of some Oligo (p-phenylenes) (OPPs) and Polycyclic Aromatic Hydrocarbons (PAHs), as efficient organocatalysts in photocatalytic CO2 transformations are the main goals of this investigation. The studies are based on density functional theory (DFT) calculations on the mechanistic aspects of C-C bond formation through a coupling reaction between CO2•- and amine radical. The reaction is performed through two successive single electron transfer steps. After careful kinetic investigations by Marcus' theory rules, powerful descriptors are used to describe the behavior of observed barrier energies of electron transfer steps. The studied PAHs and OPPs consist of different numbers of rings. Thus, it can be considered different charge densities, afforded from π electrons, of PAHs and OPPs that cause distinguished efficiency in kinetic aspects of electron transfer steps. Electrostatic Surface Potential (ESP) analyses reveal a good relationship between the charge density of the studied organocatalysts in single electron transfer (SET) steps and the kinetic parameters of the steps. Moreover, the contribution of rings in the framework of PAHs and OPPs would be another effective factor in the barrier energies of SET steps. Aromatic properties of the rings, studied by the Anisotropy of the Current-Induced Density (ACID), Nucleus-Independent Chemical Shift (NICS), the multi-center bond order (MCBO), and AV1245 Indexes, are the other impressive factors in the role of rings in SET steps. The results show that the aromatic properties of the rings are not similar to each other. Higher aromaticity affords remarkable reluctance of the corresponding ring to participate in SET steps.

Synthesis, molecular docking and dynamics studies of pyridazino[4,5-b]quinoxalin-1(2H)-ones as targeting main protease of COVID-19.

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has created a crisis in public health. Because, the 3CLpro, the main protease of SARS-CoV-2, possesses a critical role in coronavirus replication, many efforts have been devoted to developing various inhibitors to prevent the fast spread of COVID-19. In the current work, a number of various pyridazino[4,5-b]quinoxalin-1(2H)-one derivatives bearing thiadiazine and thiadiazole fragments has been prepared via a straightforward and practical strategy involving the reaction of 2-(ethoxycarbonyl)-3-formylquinoxaline 1,4-dioxide with thiocarbohydrazide under reflux conditions. To determine the bioavailability of pyridazino[4,5-b]quinoxalin-1(2H)-one derivatives, Lipinski's rule of five has been carried out. Regarding this rule, none of the synthesized compounds exhibit any deviation from Lipinski's rule of five. Furthermore, molecular docking and molecular dynamics approaches have been implemented to figure out the potential interactions of products with SARS-CoV-2 main protease. The outcomes of molecular docking studies demonstrate that the phenyl and nitrophenyl substituted pyridazino[4,5-b]quinoxalin-1(2H)-one show the lowest binding affinity among the other compounds, indicating a favorable orientation in the active site of the chymotrypsin-like cysteine protease. In addition, the MD simulation performed to evaluate the stability of the protein-ligand complex represents that the average binding energy of the nitrophenyl complex is less than that of the phenyl complex. Therefore, according to the in silico results, the inhibitory effect of the nitrophenyl complex is more significant than the phenyl complex.Communicated by Ramaswamy H. Sarma.

Nitronium salts as mild and inexpensive oxidizing reagents toward designing efficient strategies in organic syntheses; A mechanistic investigation based on the DFT insights.

Today, introducing and evaluating the performance of novel reagents are an undeniable part of designing a successful synthetic strategy. Herein, we study the efficiency and mechanism of recently synthesized nitronium salts (e.g., NO2FSO3, NO2CF3SO3, NO2HS2O7, NO2BF4, NO2PF6, and NO2HSO4) in the oxidation reaction of ethanol to acetic acid, as a model of the primary alcohol transformations to linear carboxylic acid. An aldehyde molecule is the first produced species in this reaction which is converted to the acetic acid molecule in the presence of in situ-produced nitric acid. Concerning the proposed mechanism, among the studied nitronium salts, two different behaviors can be observed in the transition state of the step in which the aldehyde molecule is formed. The calculated barrier energies of this step have been scrutinized by powerful descriptors such as Quantum Theory of Atoms in Molecules (QTAIM), Natural Bond Orbital (NBO), Electrostatic Potential (ESP) surfaces, and Activation Strain Model (ASM). The outcomes of the studied descriptors illustrate that nitronium salts have different performances in progressing the formation of the aldehyde molecule. Indeed, the likeness of the transition state of this step to the products for NO2FSO3, NO2CF3SO3, and NO2HS2O7 species is more significant than the others. Accordingly, these reagents have more potential to apply as oxidizing agents in the primary alcohol transformations to linear carboxylic acid.

Pyrido[1,2-e]purine: Design and Synthesis of Appropriate Inhibitory Candidates against the Main Protease of COVID-19.

A series of tricyclic and polycyclic pyrido[1,2-e]purine derivatives were designed and synthesized via a two-step, one-pot reaction of 2,4-dichloro-5-amino-6-methylpyrimidine with pyridine under reflux conditions. Various derivatives of pyrido[1,2-e]purine were also synthesized by substituting the chlorine atom with secondary amines. After careful physiochemical and pharmacokinetic predictions, the inhibitory effects of the synthesized compounds against the main protease of SARS-CoV-2 have been evaluated by molecular docking and molecular dynamics approaches. The in silico results revealed that among all of the studied compounds, the morpholine/piperidine-substituted pyrido[1,2-e]purine derivatives are the best candidates as effective inhibitors of SARS-CoV-2.

Evaluation and understanding the performances of various derivatives of carbonyl-stabilized phosphonium ylides in CO2 transformation to cyclic carbonates.

The kinetic and mechanism evaluations of the formation of cyclic carbonates by carbonyl-stabilized phosphonium ylides as an efficient and new class of organocatalysts are the main purposes of this research. Recently, it has been reported that tetraarylphosphonium salts play the role of organocatalysts in carbon dioxide conversion to cyclic carbonates. However, in this research, the oxygen atom of the carbonyl-stabilized phosphonium ylides was treated as the nucleophilic atom for the carbon dioxide activation. Two probable mechanisms were considered and analyzed by the energetic span model. The kinetic behavior of the carbonyl-stabilized phosphonium ylides in the carbon dioxide or ethylene oxide activation was justified by the molecular electrostatic potential (ESP) analysis at the nuclear position. However, it was confirmed that the activation strain model (ASM) was a more efficient tool in explaining the kinetic behaviors in the carbon dioxide or ethylene oxide activation. A change in the ESP value of the donor-acceptor interacting system (ΔΔVn) and distortion energy at the transition states (ΔEstrain(ζ)) were the outcomes of the ESP and ASM models, respectively, which showed a linear correlation. The electron localization function (ELF) concept was used to justify the kinetic behavior of the second step of the preferred mechanism, revealing that the electron-donating/withdrawing groups substituted on the organocatalysts have a remarkable effect on the electron density of the involved basin at the transition states. On the basis of different analyses, it was proposed that carbonyl-stabilized phosphonium ylides having electron-donating substituents are the best candidates for carbon dioxide conversion to cyclic carbonates.