Ethyl Chloroformate Research Articles

Synthesis of phosphonic analog of glutamic acid

A scheme for the synthesis of phosphonic analog of glutamic acid starting from tert-butyl N-tert-butoxycarbonylaspartate I was developed. The latter was obtained from aspartic acid by the previously described method [1, 2]. The carboxy group of compound I was acylated with ethyl chloroformate and reduced with sodium borohydride in methanol to give tertbutyl-(S)-N-(tert-butoxycarbonyl)homoserine (S)-II [2]. The latter was converted to the bromide (S)-III via the reaction with triphenylphosphine and bromotrichloromethane [3]. Bromide III was introduced into the Arbuzov reaction with trimethylsilyldiethylphosphite to yield phosphonate IV, deprotection of which with diluted hydrochloric acid resulted in the phosphorus analog of glutamic acid V.

ChemInform Abstract: Reissert‐Like Alkenylation of Azaaromatic Compounds with Alkenylzirconocene Chloride Complexes.

AbstractThe Reissert‐like alkenylation of 3,4‐dihydroisoquinoline (I) with alkenylzirconocenes (II) in the presence of ethyl chloroformate gives alkenylated tetrahydroisoquinoline (IV) regioselectively.

Determination of selenomethionine and seleno-methyl-selenocysteine in biota by ultrasonic-assisted enzymatic digestion and multi-shot stir bar sorptive extraction–thermal desorption–gas chromatography–mass spectrometry

A method based on stir bar sorptive extraction (SBSE) and thermal desorption (TD)–gas chromatography–mass spectrometry (GC–MS) has been optimized for the determination of seleno-methyl-selenocysteine (SeMetSeCys) and selenomethionine (SeMet) in biota samples. Aliquots of freeze-dried tissue, a mixture of protease XIV-lipase and water were sonicated for 2min. After extraction, the extract was separated by centrifugation and subjected to derivatization and SBSE–TD–GC–MS. The parameters affecting derivatization, absorption and desorption steps were investigated. The optimized conditions consist of a derivatization with 40μL of ethyl chloroformate (ECF) in 400μL of a water:ethanol:pyridine (60:32:8) mixture, followed by dilution to 1.5mL of 70g NaClL−1 in water at neutral pH and an extraction step using 10mm×1mm PDMS stir bar, stirring at 800rpm for 20min at room temperature (23±1°C). Three stir bars were used for the extraction of three different aliquots of the same sample and then placed in a single glass desorption liner and simultaneously desorbed for GC–MS analysis. The desorption step required the following conditions: 300°C (desorption temperature), 6min (desorption time), 50mLmin−1 (vent flow) and −5°C (cryotrapping temperature). The method provided precise (8.1%) and accurate results in the mgSekg−1 range (using the selected-ion monitoring-SIM mode) against certified reference material SELM-1 yeast, with recoveries higher than 80% for spiked algae and clams samples.

One-Pot Synthesis and Evaluation of Properties of Optically Active Poly(imide–urethane)s

Abstract A new diacylazide 2 bearing two preformed imide rings and (S)-valine was prepared in three steps, starting from the reaction of 4,4′-carbonyldiphthalic anhydride with (S)-valine in refluxing glacial acetic acid, followed by treating 4,4′-carbonylbis[(S)-2′′-phthalimidovaline] (1) with ethyl chloroformate in the presence of triethylamine, and subsequently by a nucleophilic reaction with sodium azide. A novel family of optically active poly(imide–urethane)s (PIUs) with moderate inherent viscosities in the range 0.25–0.44 dL g−1 were prepared from diacylazide 2 and various aromatic diols in dry toluene under refluxing in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO, triethylenediamine) as a catalyst. The polycondensation reaction readily proceeded in desirable yields as one-pot reactions starting from 2 without separate synthesis of the corresponding diisocyanate. All of the resulting polymers were thoroughly characterized by spectroscopic methods and specific rotation. The PIUs exhibited an excellent solubility in a variety of polar solvents. Experimental results indicated that all the PIUs had glass-transition temperature between 179 and 218 °C, the decomposition temperature at 10% weight loss between 201 and 223 °C under nitrogen.

Gas Chromatographic Analysis of Guanidino Compounds in Sera and Urine of Uremic Patients Using Glyoxal and Ethyl Chloroformate as Derivatizing Reagents

Gas chromatographic (GC) method has been developed for the determination of the guanidino compounds: guanidine (G), methylguanidine (MG), guanidinoacetic acid (GAA), guanidinopropionic acid (GPA), guanidinobutyric acid (GBA) and guanidinosuccinic acid (GSA) was carried out after precolumn derivatization with glyoxal and ethyl chloroformate from the column HP-5 (30 m × 0.32 mm i.d.) at 90°C for 3 min, followed by a heating rate 25°C/min up to 260°C with a nitrogen flow rate of 2 ml/min. Detection was by FID. The linear calibrations were obtained within 0.1-20.0 μmol/L, with limits of detection (LODs) within 0.014-0.024 μmol/L. The separation and derivatization was repeatable (n = 6) with relative standard deviations (RSD) within 0.8-1.9% in retention time and 0.5-1.8% in peak height/peak area. A number of additives and amino acids did not affect the determination. The method was applied for the determination of guanidino compounds from the serum and urine of 9 healthy volunteers and 8 uremic patients and the amounts found were in the range 0.08-0.48 and below the limit of detection (LOD) - 345 μmol/L and 1.82 - 13.88 and 0.77 - 432.0 μmol/L with RSDs within 4.2%, respectively.

Simultaneous Measurement of Serotonin, Dopamine and Their Metabolites in Mouse Brain Extracts by High-Performance Liquid Chromatography with Mass Spectrometry Following Derivatization with Ethyl Chloroformate

In order to measure the levels of serotonin (5-hydroxyltryptamine, 5-HT), dopamine (DA), 3,4-hydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT) and homovanillic acid (HVA) simultaneously, an effective derivatization method followed by high-performance liquid chromatography (HPLC) coupled to electrochemical ionization mass spectrometry was used. The derivatization reaction of biological samples with ethyl chloroformate occurred rapidly at room temperature in aqueous conditions, and the resulting derivatives were isocratically separated with good selectivity using a C18 reversed-phase column within 30 min. The study results showed that the new derivatization procedure offers an excellent means of simultaneous determination of 5-HT, DA and their metabolites in mouse brain homogenates, which are important in a number of physiological and behavioral functions.

Gas Chromatographic Determination of Guanidino Compounds Using Hexafluoroacetylacetone and Ethyl Chloroformate as Derivatizing Reagents

Guanidino compounds guanidine, methylguanidine, guanidinoacetic acid, guanidinobutyric acid, guanidinopropionic acid, and guanidinosuccinic acid after derivatization with hexafluoroacetylacetone and ethyl chloroformate at pH 9 in aqueous phase, eluted, and separated from gas chromatographic column HP-5 (30 m × 0.32 mm id) with film thickness of 0.25 μm at an initial column temperature 90 °C for 2 min, followed by heating rate of 10 °C min−1 up to 220 °C with nitrogen flow rate of 1 mL min−1. The detection was by flame ionization detector. The linear calibration ranges of each of guanidino compounds were obtained within 1–10 μg mL−1, and the limit of detection was within 0.014–0.19 μg mL−1. The derivatization and gas chromatography elution and separation were repeatable in terms of retention time and peak height/peak area with relative standard deviation (RSD) (n = 4) within 1.7–2.9 % and 1.4–2.8 %, respectively. The method was applied for the determination of guanidino compounds from deproteinized serum of uremic patients and healthy volunteers, and was found in the range below the limit of quantitation (BLOQ) to 1.25 μg mL−1 with RSD within 1.4–3.6 %, and BLOQ to 0.4 μg mL−1 with RSD 1.3–3.4 %, respectively. A number of pharmaceutical additives did not effect the determination with RSD within ±3.1 %.

Determination of Bisphenol A and Alkylphenols in Soft Drinks by High-Performance Liquid Chromatography with Fluorescence Detection

A highly sensitive and selective method was developed for the purification and determination of bisphenol A and alkylphenols in soft drinks by using 2-(11H-benzo[a]carbazol-11-yl) ethyl chloroformate (BCEC-Cl) as pre-column labeling reagent followed by high-performance liquid chromatography (HPLC) with fluorescence detection. The HPLC sensitivity of bisphenol A and alkylphenols was greatly enhanced through the introduction of BCEC-Cl moiety with excellent fluorescence property into the target molecules. Meanwhile, the introduction of highly hydrophobic BCEC-Cl moiety into the analytes also greatly increased the hydrophobicity of the target compounds and distinguished them from hydrophilic matrices. Therefore, little interference was observed. Solid-phase extraction with C18 cartridges was applied to sample purification procedure with recoveries of higher than 82 %. When 20 mL of sample was used for analysis, the limits of quantifications of the analytes were between 0.06 and 0.1 mu g L-1. The proposed method was successfully applied to the determination of the target compounds in soft drink samples with a much higher sensitivity than traditional HPLC methods.

Synthesis, pharmacological activity evaluation and molecular modeling of new polynuclear heterocyclic compounds containing benzimidazole derivatives

Novel heterocyclic compounds containing benzimidazole derivatives were synthesized from 2-(1H-benzimidazol-2-yl) acetonitrile (1) and arylhydrazononitrile derivative 2 was obtained via coupling of 1 with 4-methyl phenyldiazonium salt, which was then reacted with hydroxylamine hydrochloride to give amidooxime derivative 3. This product was cyclized into the corresponding oxadiazole derivative 4 upon reflux in acetic anhydride. Compound 4 was refluxed in DMF in the presence of triethylamine to give the corresponding 5-(1H-benzimidazol-2-yl)-2-p-tolyl-2H-1,2,3-triazol-4-amine 6. Treatment of compound 6 with ethyl chloroformate afforded 2,6-dihydro-2-(4-methylphenyl)-1,2,3-triazolo[4",5"-4',5']pyrimido[1,6-a]benzimidazole-5(4H)-one (8). 1,2-bis(2-cyanomethyl-1H-benzimidazol-1-yl)ethane-1,2-dione (10) was synthesized via the condensation reaction of 2-(1H-benzimidazol-2-yl) acetonitrile (1) and diethyloxalate. The reactivity of compound 10 towards some diamine reagents was studied. The in vitro antimicrobial activity of the synthesized compounds was investigated against several pathogenic bacterial strains such as Escherichia coli O157, Salmonella typhimurium, E. coli O119, S. paratyphi, Pseudomonas aeruginosa, Staphylococcus aureus, Listeria monocytogenes and Bacillus cereus. The results of MIC revealed that compounds 12a-c showed the most effective antimicrobial activity against tested strains. On the other hand, compounds 12a, b exhibited high activity against rotavirus Wa strain while compounds 12b, c exhibited high activity against adenovirus type 7. In silico target prediction, docking and validation of the compounds 12a-c were performed. The dialkylglycine decarboxylase bacterial enzyme was predicted as a potential bacterial target receptor using pharmacophore-based correspondence with previous leads; giving the highest normalized scores and a high correlation docking score with mean inhibition concentrations. A novel binding mechanism was predicted after docking using the MOE software and its validation.

A reliable and simple method for the assay of neuroendocrine tumor markers in human urine by solid-phase microextraction–gas chromatography-triple quadrupole mass spectrometry

Homovanillic acid (HVA), vanylmandelic acid (VMA), and 5-hydroxyindoleacetic acid (5-HIAA) are the metabolites of some catecholamines such as epinephrine, nor-epinephrine, dopamine and serotonin and their quantification is used in the diagnosis and management of patients with neurocrine tumors. A novel approach in the assay of these biomarkers in human urine samples by solid phase microextraction (SPME) combined with gas chromatography-triple quadrupole mass spectrometry (GC–QqQ-MS) is presented. A preliminary derivatization with ethyl chloroformate/ethanol was used and the corresponding derivatives were then extracted by SPME in immersion mode. The performance of five SPME fibers and three chloroformates were evaluated in univariate mode and the best results were obtained using the polyacrylate fiber and ethyl chloroformate. The variables affecting the efficiency of SPME analysis were optimized by the multivariate approach of “Experimental design” and, in particular, a central composite design (CCD) was applied. The optimum working conditions in terms of response values were achieved by performing analysis at room temperature with addition of NaCl (9.5%) and with an extraction time of 25.8min. Identification and quantification of analytes were carried out by using a gas chromatography-triple quadrupole mass spectrometry (GC–QqQ MS) system in multiple reaction monitoring (MRM) acquisition. An evaluation of all analytical parameters shows that the proposed method provides satisfactory results. Very good linearities were, in fact, achieved in the tested calibration ranges with correlation coefficient values >0.99 for all the analytes and accuracies and RSDs calculated for between-run and tested at concentrations of 1, 10, and 80mgL−1 were ranging from 91.3% to 106.6%, and from 0.5 to 8.9%, respectively. Moreover, the LOD values obtained can be considered very satisfactory (1.3, 0.046 and 24.3μgL−1 for HVA, VMA and 5-HIAA, respectively). The developed protocol represents, therefore, a simple, rapid and selective tool for assaying these acidic biomarkers in urine samples for neuroendocrine cancer diagnosis.

ChemInform Abstract: Convenient Peptide Synthesis Using Unprotected α‐Amino Acids Containing Another Hydrophilic Moiety under Basic Conditions.

AbstractPhenylalanine reacts effectively with unprotected α‐amino acids (II) containing an additional hydrophilic moiety under basic conditions via activation by ethyl chloroformate and triethylamine to afford the corresponding dipeptides.

Determination of t,t-muconic acid in urine samples using a molecular imprinted polymer combined with simultaneous ethyl chloroformate derivatization and pre-concentration by dispersive liquid–liquid microextraction

The present communication describes the preparation and evaluation of a molecularly imprinted polymer (MIP) as a solid-phase extraction (SPE) sorbent and simultaneous ethyl chloroformate (ECF) derivatization and pre-concentration by dispersive liquid-liquid microextraction (DLLME) for the analysis of t,t-muconic acid (t,t-MA) in urine samples using gas chromatography-mass spectrometry. The imprinting polymer was prepared using methacrylic acid as a functional monomer, ethylene glycol dimethacrylate as a cross-linker, 2,2-azobisisobutyronitrile as the initiator and t,t-MA as a template molecule. The imprinted polymer was evaluated for its use as a SPE sorbent by comparing both imprinted and non-imprinted polymers in terms of the recovery of t,t-MA from urine samples. Molecular modelling studies were performed in order to estimate the binding energy and efficiency of the MIP complex formed between the monomer and the t,t-MA. Various factors that can affect the extraction efficiency of MIP, such as the loading, washing and eluting conditions, were optimized; other factors that can affect the derivatization and DLLME pre-concentration were also optimized. MIP in combination with ECF derivatization and DLLME pre-concentration for t,t-MA exhibits good linearity, ranging from 0.125 to 2 μg mL(-1) (R(2) = 0.9971), with limit of detection of 0.037 μg mL(-1) and limit of quantification of 0.109 μg mL(-1). Intra- and inter-day precision was found to be <6%. The proposed method has been proven to be effective and sensitive for the selective pre-concentration and determination of t,t-MA in urine samples of cigarette smokers.

Intramolecular Cyclization Manifolds of 4-Alkylpyridines Bearing Ambiphilic Side Chains: Construction of Spirodihydropyridines or Benzylic Cyclization via Anhydrobase Intermediates

4-Alkylpyridines possessing nucleophilic β-dicarbonyl side chains have been converted to spirodihydropyridines upon treatment with ethyl chloroformate and sub-stoichiometric amounts of Ti(O(i)Pr)(4). Alternatively, inclusion of mild base in the reaction medium was found to facilitate generation of anhydrobase intermediates. Subsequent aldol-like condensations with electrophilic side chain moieties followed by hydrolysis delivered benzylically cyclized pyridines in good yield. In situ hydrogenation of cyclized anhydrobase intermediates afforded 4-substituted piperidines.

Synthesis and Antibacterial Activity of Some New S-Triazole Derivatives

Alkylation of 4-anilino-5-phenyl-4H-1,2,4-triazole-3-thiol (1) with some halo compounds yielded the corresponding sulfides 2a–f. Some sulfides 2e,f were cyclized to give triazolothiadiazines 3 and 4. Triazolothiadiazoles 5 and 6 were prepared through the reaction of compound 1 with carbon disulfide or ethyl orthoformate, respectively. Treatment of compound 1 with ethyl chloroformate or phenyl isothiocyanate yielded triazolo-thiadiazole and triazole 9 and 10, respectively. Reaction of compound 1 with Lawesson's reagent gave triazolothiadiazaphosphole derivative 11. Also, compound 1 underwent cyclocondensation reactions with some bidentate reagents to give triazolothiazines 4, 12, and 13. Triazolo-thiazepines and triaziepine 14–16 were synthesized via the reaction of compound 1 with β-ketoesters or ethyl cyanoacetate. Tricyclic systems 19 and 20 were prepared through the reaction of compound 4 with the appropriate reagent. Some synthesized compounds were tested for antibacterial activity. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Synthesis of ethoxycarbonyl isothiocyanate by orthogonal design

Using Schiff base as a phase transfer catalyst, ethoxycarbonyl isothiocyanate was synthesized by reacting ethyl chloroformate with sodium thiocyanate. In order to get the best synthetic technology, an orthogonal test (L9(34)) was applied. The results show that reaction temperature, reaction time, content of catalyst and molar ratio of sodium thiocyanate to ethyl chloroformate are the main factors influencing the yield. The four factors chosen for the present investigation are based on the results of a single-factor test. The optimum synthetic technology is determined as follows: reaction temperature 35 °C, reaction time 3 h, the content of catalyst (molar fraction based on ethyl chloroformate) 1.5% and molar ratio of sodium thiocyanate to ethyl chloroformate 1.1. Under the optimized synthetic technology, the experimental yield reaches 96.8%.

Rapid and simultaneous determination of twenty amino acids in complex biological and food samples by solid-phase microextraction and gas chromatography–mass spectrometry with the aid of experimental design after ethyl chloroformate derivatization

Amino acids play a vital role as intermediates in many important metabolic pathways such as the biosynthesis of nucleotides, vitamins and secondary metabolites. A sensitive and rapid analytical method has been proposed for the first time for the simultaneous determination of twenty amino acids using solid-phase microextraction (SPME). The protein samples were hydrolyzed by 6M HCl under microwave radiation for 120min. Then the amino acids were derivatized by ethyl chloroformate (ECF) and the ethoxy carbonyl ethyl esters of amino acids formed were extracted using SPME by direct immersion. Finally the extracted analytes on the SPME fiber were desorbed at 260°C and analyzed by gas chromatography–mass spectrometer (GC–MS) in electron ionization mode. Factors which affect the SPME efficiency were screened by Plackett–Burmann design; most significant factors were optimized with response surface methodology. The optimum conditions for SPME are as follows: pH of 1.7, ionic strength of 733mg, extraction time of 30min and fiber of divinyl benzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS). The recovery of all the amino acids was found to be in the range of 89.17–100.98%. The limit of detection (LOD) of all derivatized amino acids in urine, hair and soybean was found to be in the range of 0.20–7.52μgL−1, 0.21–8.40μgL−1 and 0.18–5.62μgL−1, respectively. Finally, the proposed technique was successfully applied for the determination of amino acids in complex biological (hair, urine) and food samples (soybean). The method can find wide applications in the routine analysis of amino acids in any biological as well as food samples.

Synthesis, Moleculer Docking and Anticancer Screening of Some Novel Tetrahydronaphthyl Thiazolyl Pyrazoles and other Related Derivatives

-pyrazole-4-carbonitrile (3) with different reagents such as triethylorthoformate, ethyl chloroformate and/or hydroxyamine hydrochloride yielded the substituted pyrazoles 4-6. Cyclocondensation of 3 with formic acid, acetic anhydride, formamide and /or acetamide afforded the pyrimidine derivatives 8-11. Reaction of 3 with carbon disulphide, substituted isothiocynate, malononitrile, aldehydes and /or chloroacetylchloride yielded the corresponding derivatives 12-16. Also, hydrolysis of 3 with conc. sulfuric acid at different conditions gave 17 and/or 18. Docking studies of the newly prepared compounds as thymidylate synthase inhibitors have been done. Some of the newly prepared compounds were evaluated as anticancer agents against three human tumor cell lines (HCT116, HePG2, MCF7).

ChemInform Abstract: New Synthesis of Multisubstituted Cyanocyclopropanes by the Intramolecular SN2 Alkylation and 1,3‐CC Insertion Reaction of Magnesium Carbenoids as the Key Reactions.

AbstractThe reaction of the compound (Ia) with other electrophiles instead of compound (IX) such as ketones, aldehydes, ethyl chloroformate gives complex mixtures.

ChemInform Abstract: Convenient Peptide Synthesis Without Protection of C‐Terminals.

AbstractA convenient protocol for the condensation of carboxylic acids with unprotected α‐amino acids via activation by ethyl chloroformate and triethylamine is presented.

Convenient Peptide Synthesis Using Unprotected α-Amino Acids Containing Another Hydrophilic Moiety under Basic Conditions

Abstract Carboxylic acids 1 and 7 reacted effectively with unprotected α-amino acids 2 containing another hydrophilic moiety under basic conditions via activation by ethyl chloroformate and triethylamine to afford the corresponding amides in 74–99% yields.