Coupling of Aryl Chlorides with Lithium Nucleophiles Enabled by Molecularly Defined Alkynyllithium Palladium Catalysts.

Palladium-catalyzed cross-couplings of aryl chlorides usually call for bulky, electron-rich ligands such as phosphines or heterocyclic carbenes. We have now found that similarly powerful cross-coupling catalysts are obtained by the reaction of palladium salts with alkynyllithium reagents. The species initially formed in this process was characterized as a dilithium tetraalkinyl palladate complex. It catalyzes the coupling of aryl chlorides with the lithium salts of various terminal alkynes to give alkynyl arenes. The isolated Li-alkynyl-Pd complex also efficiently promotes the reaction of aryl, and allyl chlorides with (hetero)aryl-, alkyl-, and allyllithium compounds as well as lithium amides. None of these reactions proceeded in the presence of palladium salts alone. The preparative utility of this approach was demonstrated by the synthesis of 49 molecules, including pharmaceutically relevant compounds.

Machine Learning to Develop Peptide Catalysts-Successes, Limitations, and Opportunities.

Peptides have been established as modular catalysts for various transformations. Still, the vast number of potential amino acid building blocks renders the identification of peptides with desired catalytic activity challenging. Here, we develop a machine-learning workflow for the optimization of peptide catalysts. First-in a hypothetical competition-we challenged our workflow to identify peptide catalysts for the conjugate addition reaction of aldehydes to nitroolefins and compared the performance of the predicted structures with those optimized in our laboratory. On the basis of the positive results, we established a universal training set (UTS) containing 161 catalysts to sample an in silico library of ∼30,000 tripeptide members. Finally, we challenged our machine learning strategy to identify a member of the library as a stereoselective catalyst for an annulation reaction that has not been catalyzed by a peptide thus far. We conclude with a comparison of data-driven versus expert-knowledge-guided peptide catalyst optimization.

Microwave-Assisted Electrostatically Enhanced Phenol-Catalyzed Synthesis of Oxazolidinones.

An electrostatically enhanced phenol is utilized as a straightforward, sustainable, and potent one-component organocatalyst for the atom-economic transformation of epoxides to oxazolidinones under microwave irradiation. Integrating a positively charged center into phenols over a modular one-step preparation gives rise to a bifunctional system with improved acidity and activity, competent in rapid assembly of epoxides and isocyanates under microwave irradiation in a short reaction time (20-60 min). A careful assessment of the efficacy of various positively charged phenols and anilines and the impact of several factors, such as catalyst loading, temperature, and the kind of nucleophile, on catalytic reactivity were examined. Under neat conditions, this one-component catalytic platform was exploited to prepare more than 40 examples of oxazolidinones from a variety of aryl- and alkyl-substituted epoxides and isocyanates within minutes, where up to 96% yield and high degree of selectivity were attained. DFT calculations to achieve reaction barriers for different catalytic routes were conducted to provide mechanistic understanding and corroborated the experimental findings in which concurrent epoxide ring-opening and isocyanate incorporation were proposed.

In silico Investigation on the Inhibiting Role of Nicotine/Caffeine by Blocking the S Protein of SARS-CoV-2 Versus ACE2 Receptor.

In this paper, we studied the in silico interaction of angiotensin-converting enzyme 2 (ACE2) human receptor with two bioactive compounds, i.e., nicotine and caffeine, via molecular dynamic (MD) simulations. The simulations reveal the efficient blocking of ACE2 by caffeine and nicotine in the exposure to the spike (S) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We have selected the two most important active sites of ACE2-S protein, i.e., 6LZG and 6VW1, which are critically responsible in the interaction of S protein to the receptor and thus, we investigated their interaction with nicotine and caffeine through MD simulations. Caffeine and nicotine are interesting structures for interactions because of their similar structure to the candidate antiviral drugs. Our results reveal that caffeine or nicotine in a specific molar ratio to 6LZG shows a very strong interaction and indicate that caffeine is more efficient in the interaction with 6LZG and further blocking of this site against S protein binding. Further, we investigated the interaction of ACE2 receptor- S protein with nicotine or caffeine when mixed with candidate or approved antiviral drugs for SARS-CoV-2 therapy. Our MD simulations suggest that the combination of caffeine with ribavirin shows a stronger interaction with 6VW1, while in case of favipiravir+nicotine, 6LZG shows potent efficacy of these interaction, proposing the potent efficacy of these combinations for blocking ACE2 receptor against SARS-CoV-2.

Cedrol protects against chronic constriction injury-induced neuropathic pain through inhibiting oxidative stress and inflammation.

Injured somatosensory nervous system cause neuropathic pain which is quite difficult to treat using current approaches. It is therefore important to find new therapeutic options. We have analyzed cedrol effect on chronic constriction injury (CCI) induced neuropathic pain in rats. The mechanical and thermal hypersensitivity were evaluated using the von Frey filament, radiant heat and acetone drop methods. The changes in the levels of biomarkers of oxidative stress including malondialdehyde (MDA) and total thiol (SH), as well as inflammatory mediators including Tumour Necrosis Factor alpha (TNF-α) and Interleukin 6 (IL-6) were estimated in the lumbar portion (L4-L6) of neuropathic rats. Administration of cedrol attenuated the CCI-induced mechanical and thermal hypersensitivity. CCI produced an increase in MDA along with a reduction in SH levels in the spinal cord of the CCI rats. Reduced levels of SH were restored by cedrol. Also, the levels of MDA were reduced in the cedrol-treated CCI rats compared to the untreated CCI rats. Besides, level of TNF-α and IL-6 increased in the spinal cord of CCI group and cedrol could reverse it. The current study showed that cedrol attenuates neuropathic pain in CCI rats by inhibition of inflammatory response and attenuation of oxidative stress.

Hydrodynamic volume of trehalose and its water uptake mechanism.

Trehalose ability to preserve water in biology has spawned research on this special disaccharide and its solutions. Trehalose unlike any other disaccharide, tend to mix with almost any amount of water. In water, Trehalose forms a hydrodynamic volume with bound waters (both coordination water and semicircular heterogeneities), capable of perturbing the very nature of normal bulk water. Switching of the two major conformational forms, defined by their helicities (i, i-H2O with lower helicity and ii, ii-H2O with higher helicity), were closely examined, using DFT/B3LYP- 6-311 + G** level of theory, along with molecular dynamic (MD) calculations in aqueous media. Patterns in radial distribution functions (RDF) confirmed semicircular heterogeneities, including spines of water (rows of slow water molecules), in Trehalose hydration shell. Dynamics of Trehalose conformational switch and its coordination water are coupled to dynamics of these spines of water, which are themselves coupled to dynamics of the rest of Trehalose hydration shell waters. Like seamless cogwheels such energy cascade links the upstream slow dynamics of spines to the downstream collective bulk water dynamics. This lubricates Trehalose conformational switch through coordination water uptake, for which we proposed a mechanism here. We show how the coupling between Trehalose and bound waters in its hydrodynamic volume encompass both function and dynamic of the molecule and its hydration shell. Further simulations are needed to see how this ability is related to the evading and percolating nature of cryoprotectant water, also reported for the self-coordinating jelly behavior of biological water.

Imbalanced Transition States from α-H/D and Remote ß-Type N-CH/D Secondary Kinetic Isotope Effects on the NADH/NAD+ Analogues in Their Hydride Tunneling Reactions in Solution.

The α-H/D (if available) and remote ß-type N-CH3/CD3 2° kinetic isotope effects (KIEs) on 10-methylacridine (MAH), 9,10-dimethylacridine (DMAH), 1,3-dimethyl-2-phenylbenzimidazoline (DMPBIH) and on the oxidized forms MA+ and DMA+, in their hydride transfer reactions with several hydride acceptors/donors in acetonitrile, were determined. The corresponding equilibrium isotope effects (EIEs) were computed. Hammett correlations of several closely related hydride transfer reactions were constructed using the literature data. The α-2° KIEs on both MAH and MA+ are inflated relative to the semiclassical prediction on the basis of the KIE/EIE comparison and Hammond's postulate. This together with previously published unusual 1° and 2° KIE behaviors strongly suggest a H-tunneling mechanism. By comparing with the EIEs, the α-2° KIEs were used to analyze the rehybridization of the reaction center C and the N-CH3/CD3 2° KIEs to calculate the charge distribution on the structure containing N during H-tunneling. The rehybridization appears to lag behind the charge development in the donor moiety. The charge distribution at the tunneling ready transition state is in agreement with the Hammett correlations; the donor is product-like, and the acceptor is reactant-like, indicative of a partial negative charge borne by the "in-flight" nucleus being "hydridic" in character. Results were compared with the α-2° KIEs on NADH/NAD+ and the Hammett correlations in closely related enzymes. The comparison implicates that the H-tunneling probability would be enhanced by these enzymes.