Direct synthesis of Cbz-protected β-amino ketones by iodine-catalyzed three-component condensation of aldehydes, ketones and benzyl carbamate

Iodine has been found to be very effective catalyst for a Mannich reaction between an aryl aldehyde, an aryl ketone and benzyl carbamate, even though this is a less reactive amine, to produce Cbz-protected β-aryl β-amino carbonyl compounds in high yields.     

Simultaneous Determination of Carbamate and Organophosphorus Pesticides in Honeybees by Liquid Chromatography-Mass Spectrometry

Summary The potential of liquid chromatography-mass spectrometry (LC-MS) has been studied for the simultaneous determination of sixteen carbamate and organophosphorus pesticides in honeybees using a traditional sample preparation protocol based on acetone extraction and dichloromethane partitioning. The performances of both atmospheric pressure chemical ionization (APCI) and electrospray (ES) interfaces were compared. APCI offered better sensitivity and specificity for a higher range of pesticides. Limits of quantification were from 0.01 to 0.17 mg kg^–1, at which recoveries obtained were between 64 and 93%, except for pirimicarb that was at 13%, with relative standard deviations ranging from 7 to 20%. Fenitrothion, fenoxycarb, methiocarb and phoxim were found in bees from Valencian Community beehives at concentrations between 0.03 and 3.75 mg kg^–1.     

Macromolecular imidazole-tenside conjugates with carbamate linkage

Polyethylene glycol tert-octylphenyl ether and polyoxyethylenesorbitan trioleate are polydisperse macromolecular detergent molecules, containing a single hydroxyl function, which was transformed by 1,1-carbonyldiimidazole into imidazole-detergent conjugates with a carbamate linkage.     

Amperometric determination of pesticides using a biosensor based on a polishable graphie-epoxy biocomposite

The determination of organophosphorus and carbamate pesticides was carried out using an amperometric transducer based on a robust, polishable and easily mechinable biocomposite. The biocomposite material contains graphite powder, a non-conducting epoxy resin and acetylcholinesterase. The enzyme retains its bioactivity in the rigid epoxy-graphite matric. Measurements were carried out with acetylhiocholine as a substrate. Thiocholine produced by enzymatic hydrolysis was oxidized electrochemically at 70 mV (vs. Ag/AgCl in pH 7.0 buffered solution with 0.1 M phosphate and 0.1 m KCl). The decrease rate of substrate steady-state current after the addition of pesticide was used for evaluation. The method of construction allows for the repetitive use of the electrode. Simple polishing procedures are used to regenerate the bioactive transducer surface.     

Pictet-Spengler reactions catalyzed by Brønsted acid-surfactant-combined catalyst in water or aqueous media

Perfluorooctanesulfonic acid (PFOSA), Brønsted acid-surfactant-combined catalyst, efficiently catalyzes the Pictet-Spengler reactions of β-arylethyl carbamate derivatives with aldehydes in water. The present reaction is accelerated by the addition of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP).     

The direct conversion of carbamates to ureas using aluminum amides

The conversion of carbamates into ureas using aluminum amide complexes is reported. This reaction is a convenient method to prepare bi-, tri- and tetra-substituted ureas from carbamate-protected primary or secondary amines by reaction with primary or secondary amines in the presence of stoichometric quantities of trimethylaluminum. A reactivity trend of the various carbamates was observed and methyl and benzyl carbamates were reacted selectively in the presence of t-butyl carbamates.     

Regioselective Re(I)-catalyzed coupling of terminal alkynes, Et2NH, and CO2 leading to anti-Markovnikov adducts

ReBr(CO)₅-catalyzed addition of Et₂NH and CO₂ to terminal alkynes afforded anti-Markovnikov adducts of alkenyl carbamates in good to excellent yield and high regioselectivity.     

Biosensors based on highly sensitive acetylcholinesterases for enhanced carbamate insecticides detection

This paper presents the construction of amperometric biosensors for the highly sensitive detection of carbamate insecticides based on the inhibition of acetylcholinesterase (AChE). This enzyme was immobilised by entrapment in an optimised sol-gel matrix on TCNQ-modified screen-printed electrodes. The enzyme activity was estimated by measuring the thiocholine produced by the enzymatic hydrolysis of the acetylthiocholine using TCNQ as mediator. Wild and genetically engineered AChEs from Drosophila melanogaster (Dm) were chosen for their high sensitivity towards insecticides, which substantially improves the LOD compared with cholinesterases from other sources. The wild type and three mutant enzymes were tested against three carbamate insecticides: carbaryl, carbofuran and pirimicard. The best LOD were obtained with the Y370A mutant for carbaryl (1 × 10⁻⁸ M), the E69W mutant for pirimicarb (2 × 10⁻⁸ M) and the I161V mutant for carbofuran (8 × 10⁻¹⁰ M). The biosensors were applied to the analysis of two potable water samples.     

Efficient catalytic aza-Michael additions of carbamates to enones: revisited dual activation of hard nucleophiles and soft electrophiles by InCl3/TMSCl catalyst system

The aza-Michael reaction of a variety of chalcones with weaker nucleophilic carbamates catalyzed by InCl₃ in the presence of TMSCl via the entry of dual activation of both hard nucleophiles (carbamates) and soft electrophiles (enones) to provide the corresponding adducts in good yields. The first example of enantioselective aza-Michael reaction of chalcones with carbamates was also investigated in the presence of the present catalyst system.