Activation of Aromatic C−F Bonds by a N-Heterocyclic Olefin (NHO)

A N-heterocyclic olefin (NHO), a terminal alkene selectively activates aromatic C−F bonds without the need of any additional catalyst. As a result, a straightforward methodology was developed for the formation of different fluoroaryl-substituted alkenes in which the central carbon–carbon double bond is in a twisted geometry.     

A Validated, Specific Stability-Indicating RP-LC Method for Moxifloxacin and Its Related Substances

A validated, specific, stability-indicating reversed-phase liquid chromatographic method has been developed for quantitative analysis of moxifloxacin and its related substances in bulk samples and pharmaceutical dosage forms in the presence of degradation products and process-related impurities. Forced degradation studies were performed on bulk samples of moxifloxacin, in accordance with ICH guidelines, using acidic, basic, and oxidizing conditions, and thermal and photolytic stress, to show the stability-indicating power of the method. Significant degradation was caused by oxidative stress and by basic conditions; no degradation was observed under the other stress conditions. The method was optimized by analysis of the samples generated during the forced degradation studies and sample solutions spiked with the impurities. Good resolution between the analyte peak and peaks corresponding to process-related impurities and degradation products was achieved on a C₁₈ column with a simple linear mobile phase gradient prepared from aqueous sodium dihydrogen orthophosphate dihydrate containing triethylamine, pH adjusted to 3.0 with orthophosphoric acid, and methanol. Detection was performed at 240 nm. Limits of detection and quantification were established for moxifloxacin and its process related impurities. When the stressed test solutions were assayed against moxifloxacin working standard solution the mass balance was always between 99.3 and 100.1%, indicating the method was stability-indicating. The method was validated in accordance with ICH guidelines, and found to be suitable for checking the quality of bulk samples of moxifloxacin at the time of release of a batch and during storage (long term and accelerated stability testing was conducted).     

Single Crystal‐to‐Single Crystal Site‐Selective Postsynthetic Metal Exchange in a Zn–MOF Based on Semi‐Rigid Tricarboxylic Acid and Access to Bimetallic MOFs

The metal ions in a neutral Zn–MOF constructed from tritopic triacid H₃L with inherent concave features, rigid core, and peripheral flexibility are found to exist in two distinct SBUs, that is, 0D and 1D. This has allowed site‐selective postsynthetic metal exchange (PSME) to be investigated and reactivities of the metal ions in two different environments in coordination polymers to be contrasted for the first time. Site‐selective transmetalation of Zn ions in the discrete environment is shown to occur in a single crystal‐to‐single crystal (SCSC) fashion, with metal ions such as Fe³⁺, Ru³⁺, Cu²⁺, Co²⁺, etc., whereas those that are part of 1D SBU sustain structural integrity, leading to novel bimetallic MOFs, which are inaccessible by conventional approaches. To the best of our knowledge, site‐selective postsynthetic exchange of an intraframework metal ion in a MOF that contains metal ions in discrete as well as polymeric SBUs is heretofore unprecedented.     

Amending the Anisotropy Barrier and Luminescence Behavior of Heterometallic Trinuclear Linear [MIILnIIIMII] (LnIII=Gd,Tb, Dy; MII=Mg/Zn) Complexes by Change from Divalent Paramagnetic to Diamagnetic Metal Ions

The sequential reaction of a multisite coordinating compartmental ligand [2‐(2‐hydroxy‐3‐(hydroxymethyl)‐5‐methylbenzylideneamino)‐2‐methylpropane‐1,3‐diol] (LH₄) with appropriate lanthanide salts followed by the addition of [Mg(NO₃)₂] ? 6 H₂O or [Zn(NO₃)₂] ? 6 H₂O in a 4:1:2 stoichiometric ratio in the presence of triethylamine affords a series of isostructural heterometallic trinuclear complexes containing [Mg₂Ln]³⁺ (Ln=Dy, Gd, and Tb) and [Zn₂Ln]³⁺ (Ln=Dy, Gd, and Tb) cores. The formation of these complexes is demonstrated by X‐ray crystallography as well as ESI‐MS spectra. All complexes are isostructural possessing a linear trimetallic core with a central lanthanide ion. The comprehensive studies discussed involve the synthesis, structure, magnetism, and photophysical properties on this family of trinuclear [Mg₂Ln]³⁺ and [Zn₂Ln]³⁺ heterometallic complexes. [Mg₂Dy]³⁺ and [Zn₂Dy]³⁺ show slow relaxation of the magnetization below 12 K under zero applied direct current (dc) field, but without reaching a neat maximum, which is due to the overlapping with a faster quantum tunneling relaxation mediated through dipole–dipole and hyperfine interactions. Under a small applied dc field of 1000 Oe, the quantum tunneling is almost suppressed and temperature and frequency dependent peaks are observed, thus confirming the single‐molecule magnet behavior of complexes [Mg₂Dy]³⁺ and [Zn₂Dy]³⁺.     

Studies towards 1,3-diol units starting from syn β-hydroxy acylsilanes

Three complementary strategies have been explored to obtain stereodefined 1,3 diols starting from easily accessible syn β-hydroxy acylsilanes: fluoride induced migrations of substituents on silicon, a Grignard addition followed by protodesilylation and Tischenko-type reactions. Preliminary data on scope and limitations of these processes are presented.     

Preparation and properties of silver nanocomposite fabrics with in situ-generated silver nano particles using red sanders powder extract as reducing agent

Nanocomposite cotton fabrics with in situ-generated silver nanoparticles (AgNPs) were prepared by using Pterocarpus santalinus (Red sanders) extract in water as a reducing agent. The formation of AgNPs was analyzed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy. The SEM analysis of nanocomposites showed the presence of spherical AgNPs with a size range of 71–90?nm. FTIR spectra showed the involvement of hydroxyl and methylene groups of cellulose matrix in reducing the silver salt into AgNPs in the presence of red sanders powder extract as reducing agent for the in situ generation of AgNPs. These nanocomposite fabrics exhibited good antibacterial activity against Gram positive and Gram negative bacteria.     

Helical supramolecular self-assembly by prolamide thymidine/uridine analogues

This report describes the syntheses of rationally designed non-sugar nucleoside as prolamide nucleosides which contain prolyl ring and pyrimidine nucleobases (uracil/thymine) via acetamide bonds. These nucleosides have propensity to form distinctive self-assembly supramolecular helical structures ubiquitously through Watson-Crick/reverse type of hydrogen bonding with nucleobases. Moreover, the prolyl acetamide backbone groups- carbonyl (-C = O) and hydroxyl (-OH) group, are also involved in strengthening of self-assembled helical structures. Importantly, both prolamide thymidine and prolamide uridine have shown two distinctive helical structural patterns, in spite of containing the same backbone. Hence thymine and uracil moieties of prolamide nucleosides are responsible for unique supramolecular helical structural architectures.     

People In The News

Abstract

In November 1999 the title of Chevalier dans I'Ordre des Palmes Academiques has been conferred by the French Government on Professor 5. Chandrasekhar, Centre for Liquid Crystal Research, Bangalore, India, in recognition of ‘outstanding work as a Researcher and Professor’. The citation also notes that the award is ‘pour services rendus a la culture Fransaise’.

The Charles Vernon Boys medal and prize has been awarded for the year 2000 to Dr Cliff Jones of the UK Defence Evaluation and Research Agency, Malvern, UK. This award is made annually by the Institute of Physics to young scientists, of not more than 35 years of age, for distinguished research in experimental physics. The award was made to Cliff Jones for outstanding contributions to the development of liquid crystal displays. His research has covered areas including new materials, addressing techniques and panel fabrication. He has made major contributions to the development of ferroelectric liquid crystal displays, and has been closely involved in this area with a major Anglo-Japanese innovation programme with Sharp Corporation. The successful outcome of this programme is a prototype 17 inch FLC flat screen television, which was recently demonstrated in Japan.     

Asymmetric synthesis of aza-diospongin A as an iNOS inducer

The synthesis of the aza-analogue of diospongin A is described. The key steps in the synthetic sequence are Mitsunobu inversion, cross olefin metathesis and intramolecular aza-Michael addition reactions. The biological activity of this new analogue was also evaluated in the induction of nitric oxide synthase and was found to be better when compared to its natural counterpart.