On the use of mixtures of organotin species for catalytic enantioselective ketone allylation--a detective story

In the presence of enantiopure MTBH(2)(monothiobinaphthol, 2-hydroxy-2[prime or minute]mercapto-1,1[prime or minute]-binaphthyl; 0.2 eq.) quantitative allylation of ArC([double bond]O)Me takes place with impure Sn(CH(2)CH[double bond]CH(2))(4)(prepared from allyl chloride, air-oxidised magnesium and SnCl(4)) to yield tert-homoallylic alcohols in 85-92% ee. In the same process highly purified, or commercial, Sn(CH(2)CH[double bond]CH(2))(4) yields material of only 35-50% ee. The origin of these effects is the presence of small amounts of the compounds, EtSn(CH(2)CH[double bond]CH(2))(3), ClSn(CH(2)CH[double bond]CH(2))(3) ClSnEt(CH(2)CH[double bond]CH(2))(2) in the tetraallyltin sample and the presence of traces of water (which inhibits achiral background reactions). All the triallyl and diallyl species enhance the stereoselectivity in the catalytic allylation reaction, the chlorides more so than the ethyl compound. Hydrolysis of ClSnEt(CH(2)CH[double bond]CH(2))(2) affords crystallographically characterised Sn(4)(mu(3)-O)(mu(2)-Cl)(2)Cl(2)Et(4)(CH(2)CH[double bond]CH(2))(4). Reaction of this latter compound with MTBH(2) leads to the most potent catalyst.     

Asymmetric aziridination with chiral allyl aminosulfoxonium ylides: synthesis of alkenyl aziridine carboxylates and palladium-catalyzed E,trans/E,cis-isomerization of an alkenyl aziridine

Chiral cyclic and acyclic allyl aminosulfoxonium ylides have been generated from aminosulfoxonium-substituted β,γ-unsaturated α-amino acids (method A) and 1-alkenyl aminosulfoxonium salts (method B) upon treatment with DBU. Their application to the asymmetric aziridination of N-tert-butyl-sulfonyl imino ester, generated either in situ (method A) or externally added (method B), gave the corresponding alkenyl aziridine carboxylates with medium to high diastereoselectivity and enantioselectivity. A highly stereoselective Pd(0)-catalyzed isomerization of an E,trans-configured alkenyl aziridine methanol derivative to its E-cis-isomer is described, which proceeded with retention of the double bond configuration.     

Expeditious Pechmann Condensation by Using Biodegradable Cellulose Sulfuric Acid as a Solid Acid Catalyst

A facile synthesis of coumarins was performed in excellent yields via Pechmann condensation by using different type of phenols and ethylacetoacetates under solvent–free media using both conventional method and microwave irradiation in short reaction times is described. The reaction workup is very simple, and the catalyst can be easily separated from the reaction mixture and reused several times in subsequent reactions.     

Degradation of Triclosan under Aerobic, Anoxic, and Anaerobic Conditions

Triclosan (2, 4, 4??-trichloro-2??-hydroxyl diphenyl ether) is a broad-spectrum antimicrobial agent present in a number of house hold consumables. Aerobic and anaerobic enrichment cultures tolerating triclosan were developed and 77 bacterial strains tolerating triclosan at different levels were isolated from different inoculum sources. Biodegradation of triclosan under aerobic, anoxic (denitrifying and sulphate reducing conditions), and anaerobic conditions was studied in batch cultures with isolated pure strains and enrichment consortium developed. Under aerobic conditions, the isolated strains tolerated triclosan up to 1?g/L and degraded the compound in inorganic-mineral-broth and agar media. At 10?mg/L level triclosan, 95?±?1.2% was degraded in 5?days, producing phenol, catechol and 2, 4-dichlorophenol as the degradation products. The strains were able to metabolize triclosan and its degradation products in the presence of monooxygenase inhibitor 1-pentyne. Under anoxic/anaerobic conditions highest degradation (87%) was observed in methanogenic system with acetate as co-substrate and phenol, catechol, and 2, 4-dichlorophenol were among the products. Three of the isolated strains tolerating 1?g/L triclosan were identified as Pseudomonas sp. (BDC 1, 2, and 3).     

Highly sensitive method for the determination of ropinirole with a lower limit of quantitation of 3.45 pg/mL in human plasma by LC‐ESI‐MS/MS: application to a clinical pharmacokinetic study

A highly sensitive, rapid assay method has been developed and validated for the estimation of ropinirole (RPR) in human plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive‐ion mode. A solid‐phase process was used to extract RPR and citalopram (internal standard, IS) from human plasma. Chromatographic separation was operated with 0.2% ammonia solution:acetonitrile (20:80, v/v) at a flow rate of 0.50 mL/min on a Hypurity C₁₈ column with a total run time of 3.2 min. The MS/MS ion transitions monitored were 261.2 → 114.2 for RPR and 325.1 → 209.0 for IS. Method validation and clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 3.45 pg/mL and the linearity was observed from 3.45 to 1200 pg/mL. The intra‐day and inter‐day precisions were in the range of 4.71–7.98 and 6.56–8.31%, respectively. This novel method has been applied to a pharmacokinetic study of RPR in humans. Copyright © 2008 John Wiley & Sons, Ltd.     

A Validated chiral LC Method for the Enantiomeric Separation of Galantamine

A rapid isocratic chiral HPLC method has been developed for the separation of R-galantamine from S-galantamine. Good resolution viz. Rs > 3 between R- and S- forms of galantamine was achieved with chiralpak AD-H (250 × 4.6 mm) column using n-hexane, 20% propionic acid in isopropanol and diethyl amine in the ratio of 80:20:0.2 (v/v) as mobile phase at ambient temperature. Flow rate was kept as 0.8 mL min⁻¹ and the elution was monitored at 289 nm. This method was further used to determine the amount of R-galantamine in pure and pharmaceutical formulations of S-galantamine. This method is capable to detect and quantitate R-galantamine to the levels of 0.21 and 0.84 μg mL⁻¹, respectively. The method was validated as per International Conference on Harmonization (ICH) guidelines in terms of limit of detection (LOD), limit of quantification (LOQ), linearity, precision, accuracy, specificity, robustness and ruggedness.     

Optical phase conjugation in laser dyes

The nonlinear optical response of four laser-active dyes (Pyridine 1, DCM, Pyridine 2 and Styryl 9) is reported at a wavelength of 532 nm. The dyes show phase conjugate reflectivities in the 5 to 85% range. Polarization discrimination experiments and comparison with the Caro-Gower model suggests thermal origin of the nonlinearity.     

Vapour phase oxidation of 4-methylanisole to anisaldehyde over V2O5 /MgO-Al2O3 catalysts

The vapour phase selective oxidation of 4-methylanisole to anisaldehyde was investigated over different V₂O₅ /MgO-Al₂O₃ catalysts at 673 K and normal atmospheric pressure. Among various catalysts investigated the 16 wt% V₂O₅ /MgO-Al₂O₃ catalyst provided good conversion and product selectivity. The MgO-Al₂O₃ mixed oxide was obtained by a co-precipitation method and V₂O₅ was impregnated from ammonium metavanadate. The MgO-Al₂O₃ support and various V₂O₅ /MgO-Al₂O₃ catalysts were characterized by means of X-ray diffraction, FT-infrared, electron spin resonance, scanning electron microscopy, ammonia and carbon dioxide chemisorption methods. The characterization results suggest that vanadia does not form layer structures on the support surface, instead interacts very strongly with the support, in particular with MgO, and forms amorphous compounds. The NH₃ and CO₂ uptake results provide an interesting information on the acid-base characteristics of these catalysts and correlate with their catalytic properties.