Selective reduction of anomeric azides to amines with tetrathiomolybdate: synthesis of beta-D-glycosylamines

A number of beta-d-glycosyl azide derivatives undergo reduction on treatment with tetrathiomolybdate to produce the corresponding beta-d-glycosylamines exclusively without anomerization under very mild and neutral reaction conditions. Acetyl, allyl, benzoyl, and benzyl protective groups are left untouched under the reaction conditions. An exclusive selectivity in the reduction of anomeric azides is observed, while the C-2 and C-6 azides are left untouched.     

A new sphingolipid from the gorgonian Junceella juncea of the Indian Ocean

A new sphingolipid, (2S,3R,4E)-1,3-dihydroxy-2-[(nonadecanoyl) amino]-octadec-4-ene (1) along with ubiquitous batyl alcohol is isolated from the gorgonian, Junceella juncea Pallas (Gorgonaceae) of the Indian Ocean. The structure of 1 is determined on the basis of 1H- and 13C-NMR, COSY, FABMS, and GC-EIMS experiments.     

Spectrophotometric determination of cobalt(II) in the presence of large amounts of iron with salicylaldehyde thiosemicarbazone

Cobalt(II) reacts instantaneously with the reagent at pH 5.0. The yellow complex has a molar absorptivity of 1.1 × 10⁴ 1 mol^?1 cm^?1. The method is applied to the determination of cobalt in steels after removal of iron with phosphate.     

Direct spectrophotometric method for the determination of cobalt with indane 1,2,3-trionetrioxime in aqueous medium

A simple, sensitive and selective Spectrophotometric method has been developed for the determination of cobalt using indane 1,2,3-trionetrioxime (ITT): The method is based on the colour reaction between ITT and cobalt(II) in sodium acetate-acetic acid buffer (pH 4.5–7.5) medium. The calibration graph for measurement at 320 nm is linear in the range 1.18–23.60g of cobalt per 25 ml, with molar absorptivity of 5.32×10⁴1mol^–1 cm^–1. The effect of interfering ions has been studied and the method was applied to the determination of cobalt in alloys, with good results.     

Aqueous polymerization of acrylonitrile by ascorbic acid–peroxodisulfate redox system

The polymerization of acrylonitrile initiated by an ascorbic acid–peroxodisulfate redox system was studied in an aqueous solution at 35°C in the presence of air. Molecular oxygen was found to have no effect on the polymerization reaction. An increase in ionic strength slightly increased the rate. The overall rate of polymerization, R_p, showed a square dependence on [monomer] and a half-order dependence on [peroxodisulfate]. A first-order dependence on [ascorbic acid] at low concentrations (<3.0 × 10^?3 mol L^?1) followed by a decrease in R_p at higher concentrations of ascorbic acid (>3.0 × 10^?3 mol L^?1) was also noted. R_p remained unchanged up to 40°C and showed a decline thereafter. Addition of catalytic amounts of cupric ions decreased the rate whereas ferric ions were found to increase the rate. Added sulfuric acid in the range (6.0?50.0) × 10^?5 mol L^?1 decreased the R_p.     

Preconcentration and determination of calcium and magnesium in brine with flow-injection systems

On-line preconcentration on a chelating resin (Dowex A-1) and elution with 0.1 M hydorchloric acid is followed by spectrophotometry based on the metal complexes formed with 1- (2-hydroxy-4-diethylamino-1-phenylazo)-2-hydroxynaphthalene-3,6-disulfonic acid. The total concentration of calcium and magnesium is determined; in a second sample, calcium is masked with a ligand buffer containing excess of barium(II) and EGTA, and magnesium is determined. The calcium concentration is measured by difference. Magnesium (1–30 μg l^?1 and calcium (8– 10 μg l^?1) in 2.5 M sodium chloride can be determined. Calcium and magnesium in analytical reagent-grade sodium chloride and potassium chloride and primary standard sodium chloride are aslo determined. The method based on the exchange between calcium ions and Mg(EDTA) is proposed to enchance the sensitivity for calcium.     

The circular chemistry conceptual framework: A way forward to sustainability in industry 4.0

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Synthesis of Monosaccharide‐Derived Spirocyclic Cyclopropylamines and Their Evaluation as Glycosidase Inhibitors

The glucose‐, mannose‐, and galactose‐derived spirocyclic cyclopropylammonium chlorides 1a – 1d, 2a – 2d and 3a – 3d were prepared as potential glycosidase inhibitors. Cyclopropanation of the diazirine 5 with ethyl acrylate led in 71% yield to a 4 : 5 : 1 : 20 mixture of the ethyl cyclopropanecarboxylates 7a – 7d , while the Cu‐catalysed cycloaddition of ethyl diazoacetate to the exo‐glycal 6 afforded 7a – 7d (6 : 2 : 5 : 3) in 93–98% yield (Scheme 1). Saponification, Curtius degradation, and subsequent addition of BnOH or t‐BuOH led in 60–80% overall yield to the Z‐ or Boc‐carbamates 11a – 11d and 12a – 12d , respectively. Hydrogenolysis of 11a – 11d afforded 1a – 1d , while 12a – 12d was debenzylated to 13a – 13d prior to acidic cleavage of the N‐Boc group. The manno‐ and galacto‐isomers 2a – 2d and 3a – 3d , respectively, were similarly obtained in comparable yields (Schemes 2 and 4). Also prepared were the differentially protected manno‐configured esters 24a – 24d ; they are intermediates for the synthesis of analogous N‐acetylglucosamine‐derived cyclopropanes (Scheme 3). The cyclopropylammonium chlorides 1a – 1d, 2a – 2d and 3a – 3d are very weak inhibitors of several glycosidases (Tables 1 and 2). Traces of Pd compounds, however, generated upon catalytic debenzylation, proved to be strong inhibitors. PdCl is, indeed, a reversible, micromolar inhibitor for the β‐glucosidases from C. saccharolyticum and sweet almonds (non‐competitive), the β‐galactosidases from bovine liver and from E. coli (both non‐competitive), the α‐galactosidase from Aspergillus niger (competitive), and an irreversible inhibitor of the α‐glucosidase from yeast and the α‐galactosidase from coffee beans. The cyclopropylamines derived from 1a – 1d or 3a – 3d significantly enhance the inhibition of the β‐glucosidase from C. saccharolyticum by PdCl , lowering the K_i value from 40 μM (PdCl ) to 0.5 μM for a 1 : 1 mixture of PdCl and 1d . A similar effect is shown by cyclopropylamine, but not by several other amines.     

Synthesis of new diheteroarylcarbazoles: a facile and simple route of 3,6-di(pyrazol-4-yl)carbazoles

A short and facile route to the synthesis of new 3,6-di(pyrazol-4-yl)carbazoles is reported. Dipyrazolylcarbazoles were synthesized in two steps from 3,6-diacetylcarbazoles through a Vilsmeier reaction which led to the formation of carbazolyl-β-chlorovinyl aldehydes, followed by cyclization with hydrazine hydrate. The reaction of the Vilsmeier reagent with hydrazones of diacetylcarbazoles yielded the corresponding pyrazole dicarbaldehydes in good yields.     

Spectrophotometric determination of copper(II) and its application to a plant sample containing zinc,iron, and manganese

Salicylaldehyde thiosemicarbazone instantaneously forms a green complex with copper(II) in the optimum pH range 5–7. A fivefold molar excess of the reagent is sufficient for the full development of the color. Beer's law is obeyed in the range 0.5–6.0 ppm of copper. The optimum concentration range as evaluated by Ringbom's method is 1.4–5.8 ppm. At 375 nm the sensitivity of the reaction and the molar absorptivity are 0.006 μg cm^?2 and 9.2 × 10³ liters mol^?1 cm^?1, respectively. The effects of pH, reagent concentration, time, order of addition of the solutions, and the interference of various ions were investigated. Copper in plant samples, containing zinc, iron, and manganese, was determined.