Organocatalyzed Enantioselective [2 + 2] Cycloaddition of ,-Cyclic Ketimines and Allenoates.

We report a novel enantioselective and regioselective [2 + 2] cycloaddition of allenoate and ,-cyclic ketimine catalyzed by a quinidine derivative. The methodology enables the synthesis of fused tricyclic azetidines with a quaternary stereogenic center exhibiting high enantioselectivities. The broad range of substrates demonstrates the generality of the protocol, and the resulting functional products can be easily converted to a variety of valuable synthons.

Mechanism and Selectivity of Copper-Catalyzed Bromination of Distal C(sp)-H Bonds.

Unactivated C(sp)-H bonds are the most challenging substrate class for transition metal-catalyzed C-H halogenation. Recently, the Yu group [Liu, T.; Myers, M.

Stereospecific [3+2] Cycloaddition of Chiral Arylallenes with C,N-Cyclic Azomethine Imines.

A novel α,β-regioselective [3+2] cycloaddition reaction of arylallene with C,N-cyclic azomethine imine is reported. The axial-to-central chirality transfer phenomenon has been disclosed with chiral allenes in the reaction. The wide substrate scope, including different functional groups and natural products, reveals the generality of the methodology.

Correction: Mechanistic details of the cobalt-mediated dehydrogenative dimerization of aminoquinoline-directed benzamides.

[This corrects the article DOI: 10.1039/D0SC02066D.].

Transdermal delivery of fluvastatin loaded nanoemulsion gel: Preparation, characterization and in vivo anti-osteoporosis activity.

The objective of present study was to develop hydrogel based nanoemulsion (NE) drug delivery system for transdermal delivery and evaluate its potential in in vivo anti-osteoporotic activity. NE was prepared using aqueous phase titration method and characterized for droplet size, zeta potential and morphology. It was then formulated into hydrogel based NE gel using carbopol 940 as gelling agent.

Development of METAL-ACTIVE SITE and ZINCCLUSTER tool to predict active site pockets.

The advent of whole genome sequencing leads to increasing number of proteins with known amino acid sequences. Despite many efforts, the number of proteins with resolved three dimensional structures is still low. One of the challenging tasks the structural biologists face is the prediction of the interaction of metal ion with any protein for which the structure is unknown.

Dehydrogenation of Formic Acid Catalyzed by a Ruthenium Complex with an N,N'-Diimine Ligand.

We report a ruthenium complex containing an N,N'-diimine ligand for the selective decomposition of formic acid to H and CO in water in the absence of any organic additives. A turnover frequency of 12 000 h and a turnover number of 350 000 at 90 °C were achieved in the HCOOH/HCOONa aqueous solution. Efficient production of high-pressure H and CO (24.

The critical size of hydrogen-bonded alcohol clusters as effective Brønsted bases in solutions.

The alkyl oxonium ion, which is a protonated alcohol, has long been proposed as a key reaction intermediate in alcohol dehydration. Nonetheless, the dynamics and structure of this simple but important intermediate species have not been adequately examined due to the transient nature of the oxonium ion. Here, we devised a model system for the key step in the alcohol dehydration reaction, in which a photoacid transfers a proton to alcohols of different basicity in the acetonitrile solvent.

A class of effective decarboxylative perfluoroalkylating reagents: [(phen)2Cu](O2CRF).

This article describes the invention of a class of effective reagents [(phen)2Cu](O2CRF) (1) for the decarboxylative perfluoroalkylation of aryl and heteroaryl halides. Treatment of copper tert-butyloxide with phenanthroline ligands, with subsequent addition of perfluorocarboxylic acids afforded air-stable copper(i) perfluorocarboxylato complexes 1. These complexes reacted with a variety of aryl and heteroaryl halides to form perfluoroalkyl(hetero)arenes in moderate to high yields.

A potential role of a substrate as a base for the deprotonation pathway in Rh-catalysed C-H amination of heteroarenes: DFT insights.

The possibility of direct introduction of a new functionality through C-H bond activation is an attractive strategy in covalent synthesis. Here, we investigated the mechanism of Rh-catalysed C-H amination of the heteroaryl substrate (2-phenylpyridine) using phenyl azide as a nitrogen source by density functional theory (DFT). For the deprotocyclometallation and protodecyclometallation processes of the title reaction, we propose a stepwise base-assisted mechanism (pathway I) instead of the previously reported concerted mechanism (pathway II).

Remote C-H Activation of Quinolines through Copper-Catalyzed Radical Cross-Coupling.

Achieving site selectivity in carbon-hydrogen (C-H) functionalization reactions is a formidable challenge in organic chemistry. Herein, we report a novel approach to activating remote C-H bonds at the C5 position of 8-aminoquinoline through copper-catalyzed sulfonylation under mild conditions. Our strategy shows high conversion efficiency, a broad substrate scope, and good toleration with different functional groups.

Role of keto-enol tautomerization in a chiral phosphoric acid catalyzed asymmetric thiocarboxylysis of meso-epoxide: a DFT study.

The mechanism of a chiral phosphoric acid catalyzed thiocarboxylysis of meso-epoxide was investigated by density functional theory (DFT) calculations (M06-2X). The nucleophilic ring opening of epoxide by thiobenzoic acid was found to proceed via a concerted termolecular transition state with a simultaneous dual proton transfer to yield the β-hydroxy thioester product. Electrostatic interactions together with the steric environment inside the chiral catalyst play an important role in determining the enantioselectivity of the reaction.

Quantitative estimation of (-)-hinokinin, a trypanosomicidal marker in , and some of its commercial formulations using HPLC-PDA.

The fruits of have been used in Ayurvedic system of medicine for pain, tastelessness, painful urination and mouth diseases. Among its various chemical constituents, (-)-hinokinin, a trypanosomicidal dibenzylbutyrolactone lignan, is found in significant quantities. For quality evaluation of fruit and its commercial formulations, there is an urgent need to develop an analytical method based on (-)-hinokinin.

Hydrogen-bond-assisted controlled C-H functionalization via adaptive recognition of a purine directing group.

We have developed the Rh-catalyzed selective C-H functionalization of 6-arylpurines, in which the purine moiety directs the C-H bond activation of the aryl pendant. While the first C-H amination proceeds via the N1-chelation assistance, the subsequent second C-H bond activation takes advantage of an intramolecular hydrogen-bonding interaction between the initially formed amino group and one nitrogen atom, either N1 or N7, of the purinyl part. Isolation of a rhodacycle intermediate and the substrate variation studies suggest that N1 is the main active site for the C-H functionalization of both the first and second amination in 6-arylpurines, while N7 plays an essential role in controlling the degree of functionalization serving as an intramolecular hydrogen-bonding site in the second amination process.

DFT prediction of multitopic N-heterocyclic carbenes using Clar's aromatic sextet theory.

Existence of several multitopic N-heterocyclic carbene (NHC) ligands with up to four carbene centers have been predicted on the basis of Clar's aromatic sextet theory. Assessment on stability and reactivity of NHCs was made by quantifying aromaticity, aromatic stabilization energy (E(aroma)), strength of carbene lone pair, proton affinity, and CuCl binding energy. On NICS(0) and HOMA scales of aromaticity, several NHCs showed high aromaticity, while E(aroma) (17.

Comparison between Tube Ileostomy and Loop Ileostomy as a Diversion Procedure.

Aim. Loop ileostomy has high complication rates and causes much patient inconvenience. This study was performed to compare the outcome of tube versus loop ileostomy in management of ileal perforations.

DPPH radical scavenging activity of tricin and its conjugates isolated from "Njavara" rice bran: a density functional theory study.

Structural, electronic, and energetic characteristics of tricin, tricin-4'-O-(erythro-β-guaiacylglyceryl)ether (TEGE), and tricin-4'-O-(threo-β-guaiacylglyceryl)ether (TTGE), isolated from "Njavara" rice bran have been studied using DFT to explain their experimentally determined radical scavenging activity (EC(50) values) in comparison with known standards such as quercetin, myricetin, and catechin. Among the three mechanisms proposed for explaining the antioxidant activity, proton coupled-electron transfer (PC-ET), sequential proton loss electron transfer (SPLET), and electron transfer-proton transfer (ET-PT), our results support the second one. The O-H bond dissociation enthalpy (BDE) and the spin density on the oxygen with the radical character are excellent descriptors of radical scavenging activity.

Assessment of stereoelectronic factors that influence the CO2 fixation ability of N-heterocyclic carbenes: a DFT study.

The CO(2) fixation ability of N-heterocyclic carbenes (NHC) has been assessed on the basis of electronic and steric properties of the N- and C-substituents, measured in terms of molecular electrostatic potential minimum, observed at the carbene lone pair region of NHC (V(min1)) as well as at the carboxylate region of the NHC-CO(2) adduct (V(min2)). Both V(min1) and V(min2) are found to be simple and efficient descriptors of the stereoelectronic effect of NHCs. The V(min)-based analysis also proved that the stereoelectronic effect of N- and C-substituents is additive.

Mechanism of epoxide hydrolysis in microsolvated nucleotide bases adenine, guanine and cytosine: a DFT study.

Six water molecules have been used for microsolvation to outline a hydrogen bonded network around complexes of ethylene epoxide with nucleotide bases adenine (EAw), guanine (EGw) and cytosine (ECw). These models have been developed with the MPWB1K-PCM/6-311++G(3df,2p)//MPWB1K/6-31+G(d,p) level of DFT method and calculated S(N)2 type ring opening of the epoxide due to amino group of the nucleotide bases, viz. the N6 position of adenine, N2 position of guanine and N4 position of cytosine.

Role of stereoelectronic features of imine and enamine in (S)-proline catalyzed Mannich reaction of acetaldehyde: an in silico study.

A detailed mechanistic investigation of sixteen possible diastereomeric pathways for the C-C bond formation step in (S)-proline catalyzed Mannich reaction of acetaldehyde with N-acetyl protected benzaldimine in acetonitrile solvent has been carried out to understand how stereoelectronic features invoke enantioselectivity of the final product. Both kinetic and thermodynamic factors of the reaction obtained using various density functional theory methods point out that si-enantiofacial nucleophilic attack of anti-enamine on the iminium carbon of the E, s-cis N-acetyl protected imine is the stereoselective pathway. Structural features of the transition states predicted that enamine in anti conformation attacks the imine through a Burgi-Dunitz trajectory to yield the stereocenter.

Synthesis of new 2-substituted-[1,3,4]-oxadiazino-[6,5-b]-indoles with H1-antihistaminic, antimuscarinic and antimicrobial activity [corrected].

New 2-substituted-[1,3,4]-oxadiazino-[5,6-b]-indoles have been prepared and tested for their antibacterial, antifungal, H1-antihistaminic and antimuscarinic activities. Among them, compounds 5b, 5d, 5k exhibited higher H1-antihistaminic activity than pheniramine maleate. Compounds 5c, 5d showed higher antibacterial activity than ampicillin against Staphylococcus aureus and E.