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PubMed2004

High-performance liquid chromatography multiresidue method for the determination of N-methyl carbamates in fruit and vegetable juices.

A rapid multiresidue method has been developed for the analysis of N-methylcarbamate insecticides (oxamyl, methomyl, propoxur, carbofuran, carbaryl, and methiocarb) in fruit and vegetable juices. The method is based on the adsorption of the N-methyl carbamates in Florisil and the subsequent extraction of pesticides using a low volume of acetone. Residue levels in juice were determined by reversed-phase high-performance liquid chromatography with fluorescence detection after postcolumn derivatization. The separation of carbamates is performed on a C8 column with water-methanol as mobile phase. Recovery studies were performed at 500-, 100-, and 10-ng/ml fortification levels, and average recoveries obtained for carbamates ranged from 79 to 109%, with relative standard deviations between 1.4 and 9.9%. The method was found to be linear over the range assayed from 10 to 1,000 ng/ml, and the detection limits for carbamates varied from 0.8 to 1.9 ng/ml.

Beverages↗
PubMed1985

Comparison of the actions of carbamate anticholinesterases on the nicotinic acetylcholine receptor.

Neostigmine (Neo), pyridostigmine (Pyr), and physostigmine (Phy) at low concentrations inhibited acetylcholine (ACh) esterase, thereby indirectly potentiating ACh enhancement of [3H]perhydrohistrionicotoxin (H12-HTX) binding to the channel sites of the nicotinic ACh receptor of Torpedo membranes. However, at higher concentrations, they inhibited ACh action due to their direct binding to the ACh receptor. They displaced binding of [3H]ACh and 125I-alpha-bungarotoxin (alpha-BGT) to the receptor sites with the following order of decreasing potency: Neo greater than Phy greater than Pyr. Furthermore, Neo and Pyr potentiated [3H] H12-HTX binding to the receptor's channel sites. Preincubation of ACh receptors with any of the three carbamates reduced the rate of binding of 125I-alpha-BGT and increased the potency of carbamylcholine in inhibiting 125I-alpha-BGT binding, suggesting that the three carbamates act as partial agonists and potentiate receptor desensitization. Although none of the three carbamates inhibited [3H]H12-HTX binding to the receptor's closed channel conformation, only Phy was a potent inhibitor of [3H]H12-HTX binding to the carbamylcholine-activated conformation. The potency of Phy was not due to the absence of positive charge since Phy methiodide acted similarly. The data suggest that the major action of the three carbamates at nicotinic cholinergic synapses is inhibition of ACh-esterase. Their interactions with the nicotinic ACh receptor are with its "receptor" as well as allosteric "channel" sites, but they differ in their effects. Neo and Pyr act mainly as partial agonists, while Phy is mostly an inhibitor of the channel in the activated receptor conformation.

Acetylcholine↗
PubMed1983

Persistence of ethyl carbamate-induced DNA damage in vivo as indicated by sister chromatid exchange analysis.

Various treatment protocols were designed to investigate sister chromatid exchanges (SCEs) induced over successive posttreatment cell cycles in bone marrow and alveolar macrophage cells following treatment of C57BL/6J X DBA/2J F1 mice by i.p. injection of ethyl carbamate (3.3 mmol/kg). The same initial extent of alkylation in bone marrow and alveolar macrophages was suggested by identical SCE frequencies produced in both cell types by a one-cycle exposure protocol. The relatively lower responses in bone marrow cells by all other protocols may be a result of its faster mean population-cycling time. Second- and third-division cell SCE data produced by the various protocols indicate persistence of SCE-inducing lesions with no evidence of repair. In spite of the demonstrated lack of repair, first-cycle ethyl carbamate treatment was less effective than was second-cycle treatment in inducing SCEs. These results could not be attributed to selection of less-damaged cells over 2 cycles or to enhanced bromodeoxyuridine sensitivity in the second-cycle treatment protocol. It is speculated that the apparent cancellation of SCEs occurring over two successive cycles in the two-cycle exposure protocol may indicate the transient presence of ethyl carbamate-induced DNA interstrand cross-links. A possible mechanism of action of ethyl carbamate involving the formation of a transient cross-link and a persistent DNA monoadduct is postulated.

Animals↗
PubMed2002

Mixed anhydrides: key intermediates in carbamates forming processes of industrial interest.

Mixed anhydrides of carbonic acid with phosphonic or carbamic acid, are mimic of relevant biological systems, and behave as key intermediates in trans-esterification processes that afford carbamates of industrial interest. They are formed in the phosphonic acids mediated or direct transesterification reaction of organic carbonates with amines to afford carbamates and have been isolated and characterised in the solid state and solution. Their conversion into the products has been demonstrated to occur with high regioselectivity. The application of such intermediates in some synthetic processes is discussed.

Anhydrides↗
PubMed1989

High-performance liquid chromatographic/mass spectrometric and high-performance liquid chromatographic/tandem mass spectrometric analysis of carbamate pesticides.

The thermospray ionization mass spectra of selected carbamate pesticides were obtained using both single-stage and triple-stage quadrupole mass spectrometry in conjunction with high-performance liquid chromatography. With the use of the single-quadrupole mass spectrometer and ammonium acetate as the mobile phase, enhanced sensitivity for the analytes of interest was obtained by monitoring the relatively intact [M + 1]+ or [M + 18]+ adduct ions. Further structural characterization of the carbamates was not readily obtainable owing to the lack of diagnostic bond cleavages. The single-stage quadrupole analyses were therefore complemented by triple-stage quadrupole analyses. Here, collisionally activated daughter ion spectra exhibited structure-specific fragmentations. In addition, the enhanced selectivity and specificity provided by tandem mass spectrometry allowed use of the technique as a rapid screening tool for carbamates without the need for the chromatographic separation step.

Carbamates↗
PubMed1979

Synthesis of quaternary 8-hydroxyquinoline and 8-hydroxyquinaldine-carbamates structurally related to cholinesterase.

The quaternary carbamates were synthesized by reaction of 8-hydroxyquinoline and 8-hydroxyquinaldine with alkylisocyanates, then quaternizing the carbamates produced with alkylhalides, aralkylhalides or sulphate. The UV spectra of the compounds obtained showed lambdamax at 285 nm. The new quaternary carbamates were found to be of high toxicity and parasymapathomimetic activity in white mice.

Animals↗
PubMed2003

Novel cinchona carbamate selectors with complementary enantioseparation characteristics for N-acylated amino acids.

The synthesis and chromatographic evaluation of the enantiomer separation capabilities of covalently immobilized calix[4]arene-cinchona carbamate hybrid type receptors derived from quinine (QN) and its corresponding C9-epimer (eQN) in different solvents are reported. The receptors display complementary enantiomer separation profiles in terms of elution order, chiral substrate specificity, and mobile phase characteristics, indicating the existence of two distinct chiral recognition mechanisms. The QN-derived receptor binds the (S)-enantiomers of N-acylated amino acids more strongly, shows preferential recognition of open-chained amino acids, and superior enantioselectivity in polar media such as methanol/acetic acid. In contrast, the eQN congener preferentially recognizes the corresponding (R)-enantiomers, displays good enantioselectivity (alpha up to 1.74) for cyclic amino acids, and enhanced stereodiscriminating properties in apolar mobile phases, e.g., chloroform/acetic acid. A comparison of the enantiomer separation profiles with those of the corresponding QN and eQN tert-butyl carbamate congeners indicates no significant level of cooperativity between the calix[4]arene module and the cinchona units in terms of overall chiral recognition, most probably as a consequence of residual conformational flexibility of the calixarene module and the carbamate linkage.

Amino Acids↗
PubMed1990

Effects of in ovo injection of carbamates on chick embryo hatchability, esterase enzyme activity and locomotion of chicks.

Carbaryl and aldicarb, two carbamate pesticides used extensively throughout the United States, are known to act as acetylcholinesterase inhibitors. We have demonstrated previously that exposure to carbaryl and aldicarb in young chicks caused persistent locomotion alterations with no correlation to esterase inhibition. In this study, we investigated the effects of these carbamates when injected in ovo to chick embryos, at two time periods (days 5 and 15) during incubation. Carbaryl dosed at 45 mg kg-1 egg weight was extremely toxic to the embryos on day 5 of incubation. Hatchability was reduced to 0% as compared to 80% when carbaryl was injected on day 15 of incubation. Aldicarb at 1.5 mg kg-1 egg weight had no major effect on hatchability when injected either on day 5 or day 15 of incubation (hatchability = 90 and 100%, respectively). Plasma, liver and brain esterases were measured in the chick at different time points during incubation and after hatching. Brain acetylcholinesterase (AChE) and liver cholinesterase (ChE) were inhibited significantly during incubation in embryos dosed on day 15 with both carbaryl and aldicarb. Liver carboxylesterase was inhibited significantly during incubation with only the carbaryl treatment. All esterase enzyme activities returned to normal after hatching. Plasma ChE and carboxylesterase levels were not affected with either carbaryl or aldicarb treatment from 8 until 47 days after hatching. Neither carbamate had any effect on brain neuropathy target esterase (NTE) activity either during incubation or after hatching. The locomotion of chicks was affected in both treatment groups until 47 days after hatching. This study indicates that carbaryl and aldicarb may cause long-term delayed alterations in the chicks.

Acetylcholinesterase↗
PubMed1992

Effects of structural variations on the rates of enzymatic and nonenzymatic hydrolysis of carbonate and carbamate esters.

The effect of structural variations on the rates of elastase-catalyzed hydrolysis of model carbonate and carbamate esters was studied using HPLC. It is shown that branching in the immediate vicinity of the carbonate or carbamate functionally results in decreased hydrolysis rates. Whereas aryl carbonates act as substrates for elastase, p-nitrophenyl butyl carbamate inhibits the enzyme. A novel method was developed for the entrapment and quantitation of 14CO2 produced upon hydrolysis of carbonyl-14C-labeled carbonate esters. This technique could be useful in studying the mechanism of enzymatic hydrolysis of this type of compound and has the potential of being adapted as a convenient method in the assessment of estrolytic activity of tissue homogenates.

Carbamates↗
PubMed2004

Separation of racemic 2,4-dinitrophenyl amino acids on zirconia-immobilized quinine carbamate in reversed-phase liquid chromatography.

Zirconia is known to be one of the best chromatographic support materials due to its excellent chemical, thermal, and mechanical stability. A quinine carbamate-coated zirconia was prepared as a chiral stationary phase for separation of enantiomers of DNP-amino acids in reversed-phase liquid chromatography. Retention and enantioselectivity of this phase were compared to those for quinine carbamate bonded onto silica. Most amino acids studied were separated on the quinine carbamate-zirconia CSP although retention was longer and chiral selectivity was somewhat lower than on the corresponding silica CSP. Increased retention and decreased selectivity are probably due to strong non-enantioselective Lewis acid-base interactions between the amino acid molecule and the residual Lewis acid sites on the zirconia surface.

Amino Acids↗
PubMed2006

Development of a multi-residue method for the determination of 18 carbamates in tobacco by high-performance liquid chromatography/positive electrospray ionisation tandem mass spectrometry.

A multi-residue method for the determination of carbamates in tobacco was developed by high-performance liquid chromatography (HPLC) triple quadrupole mass spectrometry (MS). A rapid sample preparation consisted of an extraction step with methanol, centrifugation and 1:1 dilution with aqueous 10 mM ammonium acetate. After filtration these extracts were directly analysed by reversed-phase HPLC coupled to positive electrospray ionisation tandem mass spectrometry operated in the multiple reaction monitoring mode. Capillary voltage and dwell times were optimised to reduce matrix effects and to increase sensitivity. The method was validated for the determination of 18 carbamates in three main types of raw tobacco and three tobacco products. The interday accuracy ranged between 80 and 110% with a relative standard deviation (RSD) of <30%. The limits of quantification (LOQs) ranged between 0.01 and 0.04 ppm for almost all carbamates, except aldicarb sulfone, carbofuran, and pebulate, with LOQs between 0.10 and 0.20 ppm. These LOQs were clearly below the guidance residue levels defined by the Agrochemical Advisory Committee of CORESTA, an association of organisations having scientific research relative to tobacco.

Carbamates↗
PubMed1980

Foetal and maternal rat brain acetylcholinesterase: isoenzymes changes following insecticidal carbamate derivatives poisoning.

Pregnant rats (18th day) were orally given insecticidal carbamates with anticholinesterasic properties: 50 mg/kg carbaryl, 0.1 mg/kg aldicarb, 2.5 mg/kg carbofuran and 20 mg/kg pirimicarb. The acetylcholinesterase (AChE) isoenzymes from the brain of mothers and their foetuses were separated by electrophoresis on polyacrylamide ge. The four carbamate derivatives caused a significant lowering of the percentage of the least mobile isoenzyme (isoenzyme 1) in mother. Aldicarb, carbaryl and pirimicarb also caused a significant decrease in the percentage of the first foetal isoenzyme. The second foetal isoenzyme underwent a decrease after treatment with aldicarb or carbofuran. The distribution of the foetal isoenzymes was seen to be different to that of the dams in both control and treated animals. The difference in sensitivity of the cerebral AChE to the insecticides under investigation is thought to depend on differences of the fixation of carbamate derivatives on the foetal and maternal isoenzymes.

Acetylcholinesterase↗
PubMed2002

Adamantyl tenocyclidines--adjuvant therapy in poisoning with organophosphorus compounds and carbamates.

The objective of this study was to evaluate the efficacy of thienyl phencyclidine (tenocyclidine, TCP) and its newly synthesized adamantyl derivatives containing piperidine (TAPIP), pyrolidine (TAPIR) and morpholine (TAMORF) groups, which were tested with or without standard therapy in mice poisoned with organophosphates (OPs) and carbamates. These compounds with potential activity at the N-methyl- D-aspartate and muscarinic receptors showed low acute toxicity, having LD50 values varying from 106.00 mg/kg (TCP) to >504.00 mg/kg body weight (TAMORF). TCP and its adamantyl derivatives were administered intraperitoneally (2.5 mg/kg body weight) together with atropine (10.0 mg/kg body weight) and with or without 1/4 LD50 of the oxime HI-6. Each compound administered with atropine had a therapeutic effect against poisoning with carbamates propoxur, aldicarb and Ro 02-0683 (protective ratio of tenocyclidines was from 3.99 LD50 of aldicarb to >16.00 LD50 for propoxur). However, the efficacy of those compounds in combination with atropine was lower against poisoning with the OP insecticide dichlorvos (DDVP) and chemical warfare agents soman and tabun. In soman-poisoned mice, the best therapeutic effects were obtained with the combination of HI-6 plus atropine and test compounds, with protective ratios being from 5.40 to 7.12 LD50 of soman. The results suggest that TCP and adamantyl tenocyclidines could be used in combination with atropine as antidotes in carbamate poisoning and as adjuvant therapy to HI-6 and atropine in soman poisoning.

Adamantane↗
PubMed1977

The interaction of p-nitrophenyl carbamate with urease.

1. p-Nitrophenyl carbamate and thiourea have been shown to be substrates for urease (urea amidohydrolase, EC 3.5.1.5) 2. Urease has been shown to have a lower Km, 0.67 mM, with p-nitrophenyl carbamate than with urea, 2.0 mM. 3. The V of urease for the hydrolysis of urea, p-nitrophenyl carbamate and thiourea has been shown to be the same, indicating a common rate-limiting step. 4. A mechanism has been proposed for urease where the initial rate-limiting step is the release of a molecule of ammonia from the substrates.

Carbamates↗
PubMed1976

The binding of ethyl carbamate to DNA of mouse liver in vivo: the nature of the bound molecule and the site of binding.

Ethyl carbamate, labelled at C1 with 14C, bound in vivo to liver DNA of intact and partially hepatectomised mice. Isotope (18O) enrichment was not detected in the oxygen of liver DNA of mice injected with [18O] ethyl carbamate, C2H5--18O--CO--NH2. This suggests that it was the ethyl group and not the ethoxy group which bound to DNA. Chromatographic analysis of acid hydrolysates of liver DNA from mice treated with [1-14C] ethyl carbamate provided no evidence of alkylation or other form of binding to purine or pyrimidine bases. On relatively mild acid hydrolysis the alkyl group remained bound to the "apurinic acid" fraction, while more vigorous hydrolysis lead progressively first to its separation as highly ionisable hydrophilic non-volatile compounds and then to its loss as a volatile compound. DNAase I followed by phosphodiesterase hydrolysis also split off the 14C-containing group as a volatile compound. The volatile compound was identified as ethanol. These results suggest that the alkyl group was bound as an ester to a phosphate group in the DNA chain. Results with DNA from partially hepatectomised mice did not differ from those with DNA from intact mice.

Animals↗
PubMed1995

Differentiation between organophosphate and carbamate poisoning.

We propose a novel and simple assay for the real-time differentiation between carbamate and organophosphate inhibition of cholinesterase, based on our observations of the kinetic behavior of inhibited enzyme. The assay of carbamylated cholinesterase activity over time follows a non-linear kinetic pattern, whereas that of phosphorylated enzyme activity is linear. This feature can be exploited to differentiate between carbamate and organophosphate cholinesterase inhibition. The non-linear pattern characteristic of carbamates is easily discernible at degrees of inhibition of 40% or more. In this setting, cholinesterase activity ought to be measured continuously for about 1 h to obtain the kinetic pattern of enzyme activity. The initial activity, measured during the first 5 min of assay, represents the activity of enzyme in vivo. In vitro reactivation of inhibited cholinesterase allows the estimation of full potential activity of enzyme prior to poisoning, so that percentage of inhibition can be calculated. Reactivation of carbamylated cholinesterase is obtained by the incubation of diluted enzyme at 37 degrees C for 2.5 h prior to assay, whereas phosphorylated (non-aged) enzyme is reactivated by a 30 min incubation with oximes. In cases of mild exposure to cholinesterase inhibitors (< 40% inhibition), the response of enzyme to in vitro reactivation serves as a complementary test for exposure and for the nature of the inhibitor. All the results presented in this work refer to plasma cholinesterase. Erythrocyte cholinesterase was found to behave very similarly to plasma enzyme and its results have not been reported here.

Adolescent↗
PubMed1988

Carbamate analogues of (-)-physostigmine: in vitro inhibition of acetyl- and butyrylcholinesterase.

Reaction of (-)-eseroline (1) with alkyl, aryl and aralkylisocyanates afforded a series of carbamate analogues of (-)-physostigmine (2) which were assayed for inhibition of acetyl- and butyrylcholinesterase (AChE and BChE, respectively) in vitro. Included in this study were two N-alkyl-substituted carbamates 9 and 14 obtained from (-)-eseroline (1) with dialkylcarbamoyl chlorides, and allophanates 12 and 13 obtained as by-products in the reaction of 1 and benzylcarbamoyl eseroline (8) with benzyl isocyanate. Whereas none of the analogues studied was more potent than 2 against electric eel AChE, and carbamates 6, 7 and 8 were all more than 3 times more potent against human plasma BChE than 2.

Acetylcholinesterase↗
PubMed1993

Generation of substance P carbamate in neutral aqueous solution. Relevance to inflammatory joint diseases.

High-field proton (1H) nuclear magnetic resonance (NMR) spectroscopy has been employed to evaluate the formation of substance P carbamate in aqueous solution. Equilibration of substance P with physiologically relevant concentrations of bicarbonate (2.50 x 10(-2) mol.dm-3) at pH 7.00 generated a new multiplet signal centred at 4.13 ppm in its NMR spectrum, characteristic of the alpha-proton of peptide carbamate species. High-field 1H NMR spectroscopy also demonstrated that the model dipeptide, Arg-Gly, formed a carbamate in neutral aqueous solutions containing 2.50 x 10(-2) mol.dm-3 HCO3-. The physiological significance of these results is discussed in view of the central roles of vasoactive neuropeptides in human joint diseases and the hypercapnic environment of the inflamed rheumatoid joint.

Arthritis, Rheumatoid↗