A novel synthesis of enantiopure octahydropyrrolo[3,4-b]pyrroles by intramolecular [3 + 2] dipolar cycloaddition on chiral perhydro-1,3-benzoxazines

[reaction: see text] Condensation of N-substituted glycines with chiral 3-allyl-2-formyl perhydro-1,3-benzoxazines forms an azomethine ylide that cyclizes to give octahydropyrrolo[3,4-b]pyrrole derivatives. The [3 + 2] dipolar cycloadditions are stereoespecific leading to a single diastereoisomer. The chemical yields are dependent on the reaction temperature and the presence or absence of a base.     

One-step axial acetoxylation at C-23. A new method for the functionalization of the side chain of steroid sapogenins

Treatment of steroid sapogenins with diacetoxyiodobenzene (DIB) and boron trifluoride ethyl etherate in acetic acid led to the introduction of an axial acetoxyl group at position C-23 of the side chain.     

The reaction of β-aminoenones with substituted acetonitriles. Regiospecific synthesis of 2(1H)-pyridones

Unsymmetrically substituted β-aminoenones react with malononitrile, cyanomethylphenylsulfone, benzoyl-acetonitrile and ethyl cyanoacetate, in very mild conditions, to yield regiospecifically 3-functionalized 2(1H)-pyridones in high yields.     

Double domino Knoevenagel hetero Diels-Alder strategy towards bis-pyrano-1,4-benzoquinones

Several bis-pyrano-l,4-benzoquinones have been synthesized by a double domino Knoevenagel hetero Diels-Alder reaction. The synthetic approach is highly efficient allowing the construction of complex polycyclic scaffolds with six new σ-bonds. These reactions performed more efficiently and more rapidly using microwave irradiation. The resulting bis-pyrano-1,4-benzoquinones are the first examples of a double domino Knoevenagel hetero Diels-Alder reaction. Our approach represents a novel contribution to the chemistry of 2,5-dihydroxy-l,4-benzoquinones and the first general method for the synthesis of bis-pyranobenzoquinones.     

Multipurpose chamber for the implementation of gas diffusion, dialysis, solid-phase extraction and precipitation/dissolution in continuous flow analyzers

A multipurpose chamber capable of implementing a variety of continuous separation techniques is reported. The proposed module can be used in conjunction with flow manifolds coupled on-line to optical detectors in order to develop simple autoanalyzers for full sample pretreatment. The analytical applicability of such a device is discussed with specific regard to gas diffusion, dialysis, solid-phase extraction (SPE), and precipitation/dissolution techniques. Its versatility and simplicity are among the main advantages. Four different automated analyzers based on the use of the multipurpose chamber have been developed for monitoring of different quality control parameters of liquid food samples, namely, carbon dioxide in beer, ascorbic acid in fruit juice, caffeine in soft drinks and lactose, fat and protein in milk. The results obtained were compared with those provided by the existing alternatives for the same applications in terms of sensitivity and precision.     

The triviality of continuous multipliers for the real line

It is proved without resort to calculus methods that every continuous group multiplier for R can be reduced to the identity by a continuous remultiplication. The method introduced may generalize to infinitedimensional Abelian groups such as occur in analyzing the projective representations of the Bondi-Metzner-Sachs (BMS) group.     

Experimental and DFT studies of the conversion of ethanol and acetic acid on PtSn-based catalysts

Reaction kinetics studies were conducted for the conversions of ethanol and acetic acid over silica-supported Pt and Pt/Sn catalysts at temperatures from 500 to 600 K. Addition of Sn to Pt catalysts inhibits the decomposition of ethanol to CO, CH4, and C2H6, such that PtSn-based catalysts are active for dehydrogenation of ethanol to acetaldehyde. Furthermore, PtSn-based catalysts are selective for the conversion of acetic acid to ethanol, acetaldehyde, and ethyl acetate, whereas Pt catalysts lead mainly to decomposition products such as CH4 and CO. These results are interpreted using density functional theory (DFT) calculations for various adsorbed species and transition states on Pt(111) and Pt3Sn(111) surfaces. The Pt3Sn alloy slab was selected for DFT studies because results from in situ (119)Sn M?ssbauer spectroscopy and CO adsorption microcalorimetry of silica-supported Pt/Sn catalysts indicate that Pt-Sn alloy is the major phase present. Accordingly, results from DFT calculations show that transition-state energies for C-O and C-C bond cleavage in ethanol-derived species increase by 25-60 kJ/mol on Pt3Sn(111) compared to Pt(111), whereas energies of transition states for dehydrogenation reactions increase by only 5-10 kJ/mol. Results from DFT calculations show that transition-state energies for CH3CO-OH bond cleavage increase by only 12 kJ/mol on Pt3Sn(111) compared to Pt(111). The suppression of C-C bond cleavage in ethanol and acetic acid upon addition of Sn to Pt is also confirmed by microcalorimetric and infrared spectroscopic measurements at 300 K of the interactions of ethanol and acetic acid with Pt and PtSn on a silica support that had been silylated to remove silanol groups.     

Optimisation of stir bar sorptive extraction for the analysis of volatile phenols in wines

An easy, fast and reliable analytical method is proposed for the determination of the concentration of volatile phenols (ethyl- and vinylphenols) in wines. The novel stir bar sorptive extraction (SBSE) technique is employed, following a simple and fast procedure that allows 15 samples to be extracted simultaneously using very small sample volume. Extracts are desorbed in a thermodesorption system (TDS) coupled on-line to a gas chromatograph-mass spectrometry system. The SBSE offers better recovery and linear regression coefficient (r2) for the four volatile phenols than solid-phase extraction (SPE). The mass spectrometric detection in selected ion monitoring mode contributes to the lower detection limit and good sensibility obtained with this method.     

Rapid screening of selective serotonin re-uptake inhibitors in urine samples using solid-phase microextraction gas chromatography–mass spectrometry

In this paper a solid-phase microextraction–gas chromatography–mass spectrometry (SPME–GC–MS) method is proposed for a rapid analysis of some frequently prescribed selective serotonin re-uptake inhibitors (SSRI)—venlafaxine, fluvoxamine, mirtazapine, fluoxetine, citalopram, and sertraline—in urine samples. The SPME-based method enables simultaneous determination of the target SSRI after simple in-situ derivatization of some of the target compounds. Calibration curves in water and in urine were validated and statistically compared. This revealed the absence of matrix effect and, in consequence, the possibility of quantifying SSRI in urine samples by external water calibration. Intra-day and inter-day precision was satisfactory for all the target compounds (relative standard deviation, RSD, <14%) and the detection limits achieved were <0.4 ng mL^–1 urine. The time required for the SPME step and for GC analysis (30 min each) enables high throughput. The method was applied to real urine samples from different patients being treated with some of these pharmaceuticals. Some SSRI metabolites were also detected and tentatively identified.