The anionic alkylation of easily reducible arenes. A photochemical route to nucleophilic aromatic substitution of anthracene by organolithiums

High yield nucleophilic addition ensues upon mixing tetrahydrofuran solutions of benzyllithium or cyclooctadienyllithium and anthracene at low temperatures At least part of this addition proceeds by a single electron transfer pathway. Photolysis of the resulting adducts leads to the elimination of lithium hydride, giving net nucleophilic substitution in approximately 50% yield. The analogous reaction fails with naphthalene, where photolysis of the organolithium/ arene mixture leads to dimeric products derived from the organolithium.     

Lumineszenzspektren von ein- und zweikernigen Chrom(III)-Glycin-Komplexverbindungen

The luminescence spectra of the polycrystalline compounds [Cr(CH₂NH₂COO)₃ · H₂O] and [Cr₂(OH)₂(CH₂NH₂COO)₄] are investigated in the temperature range of 120K – 4.2K. From the known crystal structure (P2_1/c =D _2h ^/5 ) of the mononuclear compound assignment of the zero-phonon bands based on crystal field theory becomes possible. Both of the highly intense phosphorescence transitions are observed at \(P_1 = 14493 cm^{ - 1} ({}^2A'' \xrightarrow{{0.0}} {}^4A) and P_2 = 14428 cm^{ - 1} ({}^2A' \xrightarrow{{0.0}} {}^4A)\) . Assignment of the accompanying vibronic bands is made from the measured infrared data. Crystal field parameters Dq, B and C are determined from the luminescence and reflectance spectra. In the case of the binuclear compound the Cr³⁺-Cr³⁺ interaction via hydroxyl brides may be described by an axchange operator \(H_{ex} = - 2 \sum\limits_{ij} {J_{ij} S_i^a \cdot S_j^a } \) and from this the energy level diagram is calculated. Both observed strong phosphorescence bands at 14369 cm^?1 and 14184 cm^?1 are assigned to \(\left| {{}^2E \cdot {}^4A_2 \rangle _{s = 2} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 2} and \left| {{}^2E \cdot {}^4A_2 \rangle _{s = 1} \xrightarrow{{0.0}}} \right| {}^4A_2 \cdot {}^4A_2 \rangle _{s = 1} \) transitions.     

Asymmetric synthesis of (+)-stagonolide C and (−)-aspinolide A via organocatalysis

A new enantioselective synthesis of two important fungal metabolites, (+)-stagonolide C and (?)-aspinolide A, has been described from readily available raw materials. Proline catalyzed asymmetric α-aminooxylation and Jorgensen’s epoxidation of aldehydes are the key reactions employed in the introduction of chirality. The formation of the 10-membered lactone core structure was finally accomplished via Steglich esterification and ring closing metathesis reactions.     

Modified Pyridine-Substituted Coumarins: A New Class of Antimicrobial and Antitubercular Agents

Some new biologically potent coumarin derivatives 7a–f, 8a–f, and 9a–f bearing modified pyridine moieties (indeno[1,2-b]pyridine, 4-azaphenanthrene and benzofuro [3,2-b]pyridine) at the sixth position were designed and synthesized. All the synthesized compounds were assayed for their antimicrobial efficiency against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Salmonella typhi, Candida albicans, and Aspergillus niger. Most of the compounds showed appreciable antimicrobial activity against the tested strains. Compounds 8b, 8c, 9b, 9d, and 9f emerged as most proficient members of the series. The antitubercular activity for all the synthesized compounds was performed against Mycobacterium tuberculosis H37R_v. Compounds 8f, 9b, and 9f exhibited promising antitubercular activity. Consequently, synthesized derivatives were found to be worthy of further investigation.     

Molecular modeling studies, synthesis, and biological evaluation of Plasmodium falciparum enoyl-acyl carrier protein reductase (PfENR) inhibitors

The search for new antimalarial agents is necessary as current drugs in the market become vulnerable due to the emergence of resistance strains of Plasmodium falciparum (P. falciparum). The biosynthetic pathway for fatty acids has been recognized and validated as an important drug target in P.falciparum. One of the important enzymes in this pathway that has a determinant role in completing the cycles of chain elongation is Enoyl-ACP reductase (ENR) also popularly known as FabI. In this paper we report the design, synthesis, and microbial evaluation of inhibitors of Plasmodium enoyl reductase (PfENR). The search for inhibitors involved a virtual screening of the iResearch database with docking simulations. One of the hits was selected and modified to optimize its binding to PfENR; this resulted in the development of analogues of N-benzylidene-4-phenyl-1,3-thiazol-2-amine. The activity of these analogues was predicted from comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models constructed from a dataset of 43 known inhibitors of PfENR. The most promising molecules were synthesized and their structures characterized by spectroscopic techniques. The molecules were screened for in vitro antimalarial activity by whole-cell assay method. Two molecules, viz. VRC-007 and VRC-009, were found to be active at 4.67 and 7.01 μM concentrations, respectively.     

Nature and properties of ultrathin nanocrystalline gold films formed at the organic-aqueous interface

Ultrathin nanocrystalline films of gold formed at different temperatures at the organic-aqueous interface have been investigated by X-ray diffraction, electron microscopy, atomic force microscopy, and electronic spectroscopy. The films are smooth and continuous over relatively large length scales and are generally approximately 100 nm thick. The size of the nanocrystals is sensitive to the reaction temperature, which also determines whether the film is metallic or an activated conductor. The surface plasmon band of gold is highly red-shifted in the films. Alkanethiols perturb the structure of the films, with the magnitude of the effect depending on the chain length. Accordingly, the position of the plasmon band and the electrical resistance of the films are affected by interaction with alkanethiols; the plasmon band approaches that of isolated nanocrystals in the presence of long-chain thiols.     

Glycosyl alkoxythioimidates as complementary building blocks for chemical glycosylation

It is reported that S-glycosyl O-methyl phenylcarbamothioates (SNea carbamothioates) have a fully orthogonal character in comparison to S-benzoxazolyl (SBox) glycosides. This complete orthogonality was revealed by performing competitive glycosylation experiments in the presence of various promoters. The results obtained indicate that SNea carbamothioates have a very similar reactivity profile to that of glycosyl thiocyanates, yet are significantly more stable and tolerate selected protecting group manipulations. These features make the SNea carbamothioates new promising building blocks for further utilization in oligosaccharide synthesis.     

A Novel Synthesis and Characterization of Titanium Superoxide and its Application in Organic Oxidative Processes

A novel, exceptionally stable titanium superoxide radical ion was prepared and its structure determined by FTIR, ESR, Raman spectroscopy, X-ray diffraction, thermogravimetric/differential thermal analysis and elemental analysis. This heterogeneous catalyst has been found to be effective for the selective oxidation of aromatic amines and phenols to the corresponding nitro aromatics and p-quinones, respectively. In addition, this non-toxic, inexpensive and reusable catalyst has also been used in aminobromination of olefins, which proceed to give the 1, 2-bromoaminated anti-Markovnikov product. A brief account of these results is summarized in this review.