Smart Synthesis of Trimethyl Ethoxysilane (TMS) Functionalized Core-Shell Magnetic Nanosorbents Fe3O4@SiO2: Process Optimization and Application for Extraction of Pesticides.

In the current study, a smart approach for synthesizing trimethyl ethoxysilane-decorated magnetic-core silica-nanoparticles (TMS-mcSNPs) and its effectiveness as nanosorbents have been exploited. While the magnetite core was synthesized using the modified Mössbauer method, Stöber method was employed to coat the magnetic particles. The objective of this work is to maximize the magnetic properties and to minimize both particle size (PS) and particle size distribution (PSD). Using a full factorial design (2k-FFD), the influences of four factors on the coating process was assessed by optimizing the three responses (magnetic properties, PS, and PSD). These four factors were: (1) concentration of tetraethyl-orthosilicate (TEOS); (2) concentration of ammonia; (3) dose of magnetite (Fe3O4); and (4) addition mode. Magnetic properties were calculated as the attraction weight. Scanning electron microscopy (SEM) was used to determine PS, and standard deviation (±SD) was calculated to determine the PSD. Composite desirability function (D) was used to consolidate the multiple responses into a single performance characteristic. Pareto chart of standardized effects together with analysis of variance (ANOVA) at 95.0 confidence interval (CI) were used to determine statistically significant variable(s). Trimethyl ethoxysilane-functionalized mcSNPs were further applied as nanosorbents for magnetic solid phase extraction (TMS-MSPE) of organophosphorus and carbamate pesticides.

Synthesis of Natural (-)-Antrocin and its Enantiomer via Stereoselective Aldol Reaction.

The total synthesis of (-)-antrocin and its enantiomer are presented. Antrocin (-)-1 is an important natural product which acts as an antiproliferative agent in a metastatic breast cancer cell line (IC50: 0.6 µM). The key features of this synthesis are: (a) selective anti-addition of trimethylsilyl cyanide (TMSCN) to α,ß-unsaturated ketone; (b) resolution of (±)-7 using chiral auxiliary L-dimethyl tartrate through formation of cyclic ketal diastereomers followed by simple column chromatography separation and acid hydrolysis; (c) substrate-controlled stereoselective aldol condensation of (+)-12 with monomeric formaldehyde and pyridinium chlorochromate (PCC) oxidation for synthesis of essential lactone core in (-)-14; and (d) non-basic Lombardo olefination of the carbonyl at the final step to yield (-)-antrocin. In addition, (+)-9 cyclic ketal diastereomer was converted to (+)-antrocin with similar reaction sequences.

(R)- and (S)-4-Amino-3-(trimethylsilyl)methylbutanoic acids ameliorate neuropathic pain without central nervous system-related side effects.

Neuropathic pain is a chronic pain condition resulting from neuronal damage, and is usually treated with pregabalin or gabapentin, which are structurally related to γ-aminobutyric acid (GABA) and are originally developed as anticonvulsant drugs. Here, we report the synthesis and pharmacology of (R)- and (S)-4-amino-3-(trimethylsilyl)methylbutanoic acids (1a and 1b), which showed analgesic activity as potent as that of pregabalin in the Chung spinal nerve ligation model. However, unlike pregabalin, 1a and 1b do not have antiepileptic effects, and they are therefore promising candidates for selective therapeutic agents to treat neuropathic pain without central nervous system-related side effects.

The design, synthesis and antiviral evaluation of a series of 5-trimethylsilyl-1-beta-D-(arabinofuranosyl)uracil phosphoramidate ProTides.

BACKGROUND: Nucleoside analogues always require phosphorylation to be active. This appears to be a particular limitation for uridine-based nucleosides. Our ProTide method allows the direct use of masked membrane-soluble preformed nucleoside phosphates, bypassing the need for the initial phosphorylation step. We herein applied it to some novel 5-trimethylsilyl arabinosyl uridines. METHODS: 5-Trimethylsilyl-1-beta-D-(arabinofuranosyl)uracil was prepared in six steps starting from uridine, and five phosphoramidate ProTide derivatives were synthesized. These compounds were investigated for activity against a range of DNA and RNA viruses, including herpes simplex virus type-1 and type-2, vaccinia virus and HIV. RESULTS: Overall, these compounds did not show significant antiviral activity against any of the viruses tested. CONCLUSIONS: The inactivity of the ProTides of this nucleoside could correspond with poor ProTide activation in vitro, poor onward metabolism or low activity of the putative monophosphate metabolite.

Enantioselective synthesis of beta-iodo Morita-Baylis-Hillman esters by a catalytic asymmetric three-component coupling reaction.

A catalytic route toward chiral Morita-Baylis-Hillman esters by asymmetric coupling between alpha,beta-acetylenic esters, aldehydes, and trimethylsilyl iodide has been developed (see scheme). The reaction proceeds with high to excellent enantioselectivities, and the products can be transformed into beta-branched derivatives in a single step and with excellent retention of configuration. TMS = trimethylsilyl.

Multiresidue analysis of pollutants as their trimethylsilyl derivatives, by gas chromatography-mass spectrometry.

This paper reports a multiresidue analysis procedure which permits the identification and quantification of sixty-three water-soluble pollutants. Subsequent to their solid-phase extraction (SPE) enrichment, analyses of species have been carried out from one solution, by a single injection, as their trimethylsilyl-oxime ether/ester derivatives, by gas chromatography-mass spectrometry, within 31min. Based on our optimized extraction, derivatization and mass fragmentation studies separation have been performed in the total ion current mode, identification and quantification of compounds have been carried out on the basis of their selective fragment ions. Including various pharmaceuticals, benzoic acid, its substituted species, different aromatic carboxylic acids, cholic acids, unsaturated and saturated fatty acids, aliphatic dicarboxylic acids, as well as synthetic pollutants of various origins (2,4-di-tert-butylphenol, different phthalates). Standard compounds were added to 500 mL effluent wastewater samples, at three concentrations (1-5 microg/L, 5-10 microg/L and 10-20 microg/L). Recoveries, using the Waters Oasis cartridges performing extractions at pH 2, pH 4 and pH 7 proved to be the optimum at pH 4 (average recoveries (94.5%), except for cholesterol (10%), paracetamol (18%) and 2,5-dihydroxybenzoic acid (25%). Carbamazepine could be recovered at pH 7, only. Responses, obtained with derivatized standards proved to be linear in the range of 4-80 microg/L levels. Limit of quantitation values varied between 0.92 ng/L (4-hydroxyphenylacetic acid) and 600 ng/L (dehydrocholic acid) concentrations. One of the most important messages of this work is the confirmation of the origin of blank values. It was shown that contaminants, mainly 2,4-di-tert-butylphenol, different phthalates and fatty acids, are sourced both from the reagents and mainly from the SPE procedure, independent on the cartridge applied. Reproducibilities, characterized with the relative standard deviations (RSDs) of measurements, varied between 0.71% and 10%, with an average of 4.38% RSD. The practical utility of the method was shown by the identification and quantification of the pollutant contents of Hungarian influent and effluent wastewaters (for six consecutive months and that of the Danube River for 2 months).

Direct asymmetric intermolecular aldol reactions catalyzed by amino acids and small peptides.

In nature there are at least nineteen different acyclic amino acids that act as the building blocks of polypeptides and proteins with different functions. Here we report that alpha-amino acids, beta-amino acids, and chiral amines containing primary amine functions catalyze direct asymmetric intermolecular aldol reactions with high enantioselectivities. Moreover, the amino acids can be combined into highly modular natural and unusual small peptides that also catalyze direct asymmetric intermolecular aldol reactions with high stereoselectivities, to furnish the corresponding aldol products with up to >99 % ee. Simple amino acids and small peptides can thus catalyze asymmetric aldol reactions with stereoselectivities matching those of natural enzymes that have evolved over billions of years. A small amount of water accelerates the asymmetric aldol reactions catalyzed by amino acids and small peptides, and also increases their stereoselectivities. Notably, small peptides and amino acid tetrazoles were able to catalyze direct asymmetric aldol reactions with high enantioselectivities in water, while the parent amino acids, in stark contrast, furnished nearly racemic products. These results suggest that the prebiotic oligomerization of amino acids to peptides may plausibly have been a link in the evolution of the homochirality of sugars. The mechanism and stereochemistry of the reactions are also discussed.

Pitfalls in trimethylsilylation of anabolic steroids. New derivatisation approach for residue at ultra-trace level.

Mixtures such as N-methyl-N-trimethylsilyl-trifluoroacetamide (MSTFA), ammonium iodide and dithioerythreitol (DTE) or MSTFA, trimethyliodosilane and DTE were used for derivatisation of anabolic steroids extracted from 2 g kidney fat and present at ng kg(-1) level. They are leading to unexpected products. Their identity and mechanism of formation have been discussed. A new silylation mixture was developed to overcome these pitfalls: N,O-bis-trimethylsilyl-acetamide was used in combination of 2.5% of MSTFA/I(2) (1000:10 (v/w)). A single product consisting in ether-TMS and/or enol-TMS derivative was observed for all tested steroids with a stability demonstrated for at least 48 h. Quantitative application was proved even at the low ng kg(-1) level in a complex biological matrices, i.e. kidney fat.

Quantitative measurement of 3-O-methyl-D-glucose by gas chromatography-mass spectrometry as a measure of glucose transport in vivo.

Existing methods of measuring glucose kinetics are subject to errors. There is considerable interest in improved methods of measuring glucose kinetics to allow the development of new regimes for the treatment of diabetes mellitus. 3-O-Methyl-D-glucose is transported but not metabolized and therefore allows independent estimation of transport parameters. We describe a method by which 3-O-methyl-D-glucose in plasma samples can be measured in protocols during which glucose flux is assessed with simultaneous use of two isotopically labeled glucoses to quantitate and validate measurements of the rate of glucose appearance and disappearance. Quantitative gas chromatographic/mass spectrometric (GC/MS) analysis of 3-O-methyl-D-glucose, D-glucose, D-[U-13C] glucose and D-[6,6-2H2] glucose in human plasma using methoxime-trimethylsilyl ether derivatives is described. Measurements of all four derivatives were performed together in a small sample volume (50 microliters) with high precision. The intra-assay (inter-assay) coefficients of variation at an isotope content of 0.25 atom% excess for D-[6,6-2H2] glucose, D-[U-13C] glucose and 3-O-methyl-D-glucose were 0.8% (1.0%), 0.5% (4.0%) and 0.1% (3.7%), respectively. This method provides the basis for quantitative estimation of parameters of glucose kinetics in man and the rates of glucose flux across the cell membrane.

Determination of beta 2-agonists in hair by gas chromatography/mass spectrometry.

A method is described for the determination of the beta 2-agonists clenbuterol and salbutamol in hair. The method involves washing hair in sodium dodecyl hydrogensulphate solution, chemical digestion of the hair matrix in alkaline medium, solid-phase extraction, derivatization with methylboronic acid and analysis by gas chromatography/electron impact mass spectrometry in either the selected-ion monitoring or the scan mode. the effects of chemical digestion and of extraction on the recovery of the analytes were evaluated. Derivatization with methyl-boronic acid was compared with trimethylsilylation for GC/MS analysis of hair extracts, and was found to give mass spectra which showed more structural information with less chemical noise and better sensitivity. The proposed method was tested on real hair samples obtained from guinea pigs treated with growth-promoting doses of clenbuterol and salbutamol. Both compounds could be detected in hair of treated animals.

Pre-column derivatization of free bile acids for high-performance liquid chromatographic and gas chromatographic-mass spectrometric analysis.

Pentachlorophenyl (PCP) esters of five free bile acids (FBA) were obtained by reacting the FBA and Kovacs' complex (KC) in a 1:8 molar ratio in acetone at 65 degrees C, and were purified by column chromatography on silica gel. The esters were crystallized from benzene-hexane, derivatized as trimethylsilyl ethers for gas chromatography on a DB-1 capillary column and for gas chromatography-mass spectrometry with a DB-5 column, and mass spectrometry (MS) in the electron-impact (EI) positive-ion mode at 70 eV. The reaction is specific for FBA even in the presence of glycine and taurine conjugates of bile acids. The PCP esters were treated with benzylamine in chloroform or methanol to produce N-benzyl derivatives of FBA. The N-benzylamides were separated by high-performance liquid chromatography (HPLC) on a 4-microns Nova-Pak C18 column, studied by thermospray-LC-MS, and in the direct insertion probe-EI positive-ion mode.

Studies on anabolic steroids--4. Identification of new urinary metabolites of methenolone acetate (Primobolan) in human by gas chromatography/mass spectrometry.

The metabolism of methenolone acetate (17 beta-acetoxy-1-methyl-5 alpha-androst-1-en-3-one), a synthetic anabolic steroid, has been investigated in man. After oral administration of a 50 mg dose of the steroid to two male volunteers, twelve metabolites were detected in urine either in the glucuronide, sulfate or free steroid fractions. Methenolone, the parent steroid was detected in urine until 90 h after administration. Its cumulative urinary excretion accounted for 1.63% of the ingested dose. With the exception of 3 alpha-hydroxy-1-methylen-5 alpha-androstan-17-one, the major biotransformation product of methonolone acetate, metabolites were excreted in urine at lower levels, through minor metabolic routes. Most of methenolone acetate metabolites were isolated from the glucuronic acid fraction, namely methenolone, 3 alpha-hydroxy-1-methylen-5 alpha-androstan-17-one, 3 alpha-hydroxy-1 alpha-methyl-5 alpha-androstan-17-one, 17-epimethenolone, 3 alpha,6 beta-dihydroxy-1-methylen-5 alpha-androstan-17-one, 2 xi-hydroxy-1-methylen-5 alpha-androstan-3,17-dione, 6 beta-hydroxy-1-methyl-5 alpha-androst-1-en-3,17-dione, 16 alpha-hydroxy-1-methyl-5 alpha-androst-1-en-3,17-dione and 3 alpha,16 alpha-dihydroxy-1-methyl-5 alpha-androst-1-en-17-one. Interestingly, the metabolites detected in the sulfate fraction were isomeric steroids bearing a 16 alpha- or a 16 beta-hydroxyl group, whereas 1-methyl-5 alpha-androst-1-en-3,17-dione was the sole metabolite isolated from the free steroid fraction. Steroids identity was assigned on the basis of the mass spectral features of their TMS ether, TMS enol-TMS ether, MO-TMS, and d9-TMS ether derivatives and by comparison with reference and structurally related steroids. The data indicated that methenolone acetate was metabolized into several compounds resulting from oxidation of the 17-hydroxyl group and reduction of A-ring substituents, with or without concomitant hydroxylation at the C6 and C16 positions.

Biotransformation of diethenylbenzenes. II. Metabolic pattern of 1,4-diethenylbenzene.

The metabolism of 1,4-diethenylbenzene in the rat was followed by gas chromatographic-mass spectrometric analysis of urine using three different derivatization procedures: (i) methylation-acetylation; (ii) methylation-trimethylsilylation; (iii) methylation followed by conversion into trimethylsilyloximes. Fifteen metabolites were found in the urine of rats dosed with a single intraperitoneal injection of 1,4-diethenylbenzene (300 mg/kg). Nine of them were identified in our previous study [I. Lindhart et al., Xenobiotica, 19 (1989) 645], but the other six have not previously been reported. New metabolites, namely, 1-ethenyl-4-(1-hydroxyethyl)benzene, 4-(1,2-dihydroxyethyl)benzoic acid, (4-carboxymethylphenyl)acetylglycine, N-acetyl-S-[2-carboxy-1-(4-ethenylphenyl)ethyl]-L-cysteine, and two isomeric beta-D-glucosiduronates derived from 1-(4-ethenylphenyl)ethane-1,2-diol, were identified by mass spectrometry of their derivatives and comparison of them with the spectra of analogous metabolites of styrene and 4-methylstyrene. Acetylation of methylated urine extracts seems to be the most suitable derivatization procedure, but a combination of at least two procedures is needed if the virtually complete metabolic pattern of diethenylbenzene is to be obtained. Possible routes of biotransformation leading to the newly identified metabolites are discussed.

Retinobenzoic acids. 5. Retinoidal activities of compounds having a trimethylsilyl or trimethylgermyl group(s) in human promyelocytic leukemia cells HL-60.

The retinoidal activities of trimethylsilyl or trimethylgermyl-containing retinobenzoic acids are discussed on the basis of differentiation-inducing activity on human promyelocytic leukemia cells HL-60. Compounds with a trimethylsilyl or trimethylgermyl group at the meta position of the generic formula 2 have more potent activities than the corresponding retinobenzoic acids with a m-tert-butyl group. Compounds having two m-trimethylsilyl or -trimethylgermyl groups also have strong activities, and (E)-4-[3-[3,5-bis(trimethylsilyl)phenyl]-3-oxo-1-propenyl]benzoic acid (22, Ch55S) and (E)-4-[3-[3,5-bis(trimethylgermyl)phenyl]-3-oxo-1- propenyl]benzoic acid (35, Ch55G) are more active than retinoic acid by 1 order of magnitude. However, in the para-substituted chalcone derivatives, the replacement of a tert-butyl group (49, Ch40) with a trimethylsilyl (27, Ch40S) or a trimethylgermyl (30, Ch40G) group caused the disappearance of the activity.

Determination of 17-hydroxyprogesterone in plasma by gas chromatography-mass spectrometry with high-resolution selected-ion monitoring.

A method for determining 17-hydroxyprogesterone in plasma by isotope dilution-mass spectrometry is described. For the internal standard 17-hydroxy [2H4]progesterone is used. Extraction of plasma is followed by conversion into the 3,20-dienol,17-tristrimethylsilyl ether derivative and analysis by capillary gas chromatography-mass spectrometry with selected-ion monitoring, at a resolution of 6000. The lower limit of quantitation was 1 pg, judged from a criterion of a signal-to-noise ratio of 10. The precision and accuracy of the method were satisfactory.

Gas chromatography-mass spectrometry of monohydroxyeicosatetraenoic acids as their methyl esters trimethylsilyl, allyldimethylsilyl and tert.-butyldimethylsilyl ethers.

The gas chromatographic and mass spectrometric properties of the monohydroxy acids 5-hydroxyeicosatetraenoic acid (5-HETE), 12-hydroxyeicosatetraenoic acid (12-HETE) and 15-hydroxyeicosatetraenoic acid (15-HETE) as their methyl ester trimethylsilyl, methyl ester allyldimethylsilyl and methyl ester tert.-butyldimethylsilyl ethers were investigated. The gas chromatographic properties of the trimethylsilyl and tert.-butyldimethylsilyl derivatives were found to be excellent while the allyldimethylsilyl derivative required a well deactivated column. The mass spectra of these silyl derivatives with the exception for 12-HETE did not exhibit particularly intense ions in the upper mass region. A quantitative analysis by selected-ion monitoring of the most intense ion in the upper mass region of respective mass spectrum demonstrated that a detection limit in the low picogram range could only be obtained for 12-HETE. Since the mass spectra indicated that the double bonds exerted a strong influence on the fragmentation pattern, the trimethylsilyl, allyldimethylsilyl and tert.-butyldimethylsilyl ethers of the methyl esters of the reduced analogues of the monohydroxy acids were prepared. The saturation of the double bonds completely altered the fragmentation patterns and very intense ions carrying a high percentage of the total ion abundance were found in all of the mass spectra. The developed technique was utilized for measurements of 5-HETE in lung tissue samples from patients with lung cancer.

Preparation of enol-tert.-butyldimethylsilyl and mixed tert.-butyldimethylsilyl-trimethylsilyl ethers for gas chromatography--mass spectrometry of steroids and bile acids.

Conditions are described for conversion of testosterone into the 3-enol, 17-bis-tert.-butyldimethylsilyl ether derivative without formation of side products. The steroid is treated with tert.- butyldimethylsilylimidazole in heptane at 100 degrees C using sodium formate as catalyst. Derivatives are also formed at different rates of 3-keto-5 alpha, 3 alpha/beta-hydroxy-, 6 alpha/beta-hydroxy-, 7 beta-hydroxy-, 16 alpha-hydroxy-, 17 beta-hydroxy(sec.)- and 20 alpha/beta-hydroxysteroids, whereas hydroxyl groups in 1 beta, 7 alpha, 12 alpha/beta, 15 beta and 17 alpha(tert.) positions do not react to a significant extent. These positions are derivatized by subsequent addition of trimethylsilylimidazole , yielding mixed derivatives which are suitable for gas chromatography--mass spectrometry with selected ion monitoring. Conditions are given for conversion of some biologically important androgens, progestins and bile acids into a single form of derivative. The use of the method is illustrated by an analysis of steroids in a rat testis.

Synthesis of 2-(trimethylsilyl)ethyloxycarbonylamino acids and their use in peptide chemistry.

2-(Trimethylsilyl)ethyl-4-nitrophenyl carbonate has been prepared as a new reagent for the introduction of the 2-(trimethylsilyl)ethyloxycarbonyl group into amino acids or amino acid derivatives. The resulting N alpha-protected amino acids were found to represent suitable intermediates for the synthesis of peptides. The amino-protecting group proved to be stable under the usual conditions of peptide synthesis and readily cleaved in selective conditions via fluoride ion-mediated fragmentation.