Organic syntheses on the microgram scale. XI. Acylation of hydroxy steroids

Summary Procedures are described for the acylation of 20–35g of hydroxy steroids. The reactions are performed on thin-layer silica gel plates. Acetic anhydride-pyridine and benzoyl chloride-pyridine mixtures are used as acylating agents. Dihydroxy steroids yield two products while trihydroxy steroids yield three products. Separation and purification of the reaction products are carried out on the same plate. Several hydroxy steroids can be simultaneously acylated on one thin-layer plate, and the microsyntheses are completed in about 2 hr. The steroid ester is identified by (a) comparision with authentic sample using thin-layer chromatography, or (b) hydrolysis to give the parent hydroxy steroid, or (c) mass spectrometry.

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Organische Synthesen im Mikrogratnm-Maßstab. XI Acylierung von Hydroxysteroiden

Zusammenfassung Verfahren zur Acylierung von 20–35g Hydroxysteroiden wurden beschrieben. Die Reaktionen werden auf Kieselgel-Dünnschichtplatten durchgeführt. Mischungen aus Essigsäureanhydrid und Pyridin bzw. aus Benzoyl-chlorid und Pyridin wurden verwendet. Dihydroxysteroide bilden zwei, Trihydroxysteroide drei verschiedene Reaktionsprodukte. Deren Trennung und Reinigung erfolgt auf derselben Platte. Mehrere Hydroxysteroide können gleichzeitig auf einer Platte acyliert und die entsprechenden Reaktionen in etwa 2 Stunden durchgeführt werden. Die Steroidester werden entweder durch Vergleich mit einem Standardpräparat auf der Dünnschichtplatte oder durch Hydrolyse oder aber massenspektrometrisch identifiziert.

     

At-line coupling of UPLC to chip-electrospray-FTICR-MS

Since highly sensitive on-line coupling of UPLC with FTICR-MS is technically infeasible due to their different scan rates, at-line coupling of these techniques was developed for rapid analysis. To enable cutting of one peak of the chromatogram into one fraction, several conditions and relationships were investigated, e.g. the optimum volume of the inserted delay loop, the relationship between retention time, loop outlet drop speed, individual drop volume versus mobile phase composition under constant speed, and linear solvent strength gradient elution modes. Good and reproducible results were achieved applying UPLC as an efficient separation and fast fractionation tool before the FTICR-MS measurements. A chip-based nanoelectrospray ionization system was employed which was perfectly suited to handling the small-volume fractions and was thus chosen for the at-line coupling. The method was initially applied to spiked extracts of cell-free bacterial culture supernatants in which bacterial signalling compounds, namely N-acyl homoserine lactones (AHL), were detected. Good reproducibility and high recovery was observed. Afterwards, a culture supernatant of Erwinia sp. JX3.2, a putative AHL producer, was investigated and N-hexanoyl-homoserine lactone was determined as a possible signalling molecule. More reliable assignments were achieved by use of at-line coupling of UPLC and FTICR-MS compared with off-line measurements. Xiaojing Li and Agnes Fekete have contributed equally to this publication.     

End‐functionalized polylactides using a calcium‐based precatalyst: Synthesis and insights by mass spectrometry

A simple and convenient method for the synthesis of end functionalized polylactides (PLAs) under mild conditions by ring opening polymerization (ROP) in the absence of potentially toxic catalysts is described. Various alcohols were used as initiators in combination with Ca[N(SiMe₃)₂]₂(THF)₂ as the precatalyst in THF at room temperature. Tailored end functionalities were obtained in a controlled fashion. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐ToF‐MS) and electrospray ionization quadrupole time of flight mass spectrometry (ESI‐Q‐ToF‐MS) analysis were performed to investigate the end groups. The results confirmed that the end group fidelity was maintained in the isolated PLAs. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 437–448     

Infrared spectroscopy of acetic acid and formic acid aerosols: pure and compound acid/ice particles

Acetic acid aerosol particles, formic acid aerosol particles and mixed acid/ice particles were generated in a collisional cooling cell at a temperature of 78 K and investigated using in situ rapid scan Fourier transform infrared spectroscopy. The infrared spectra reveal that the internal structure of the particles critically depends on the particle formation conditions and, especially for the mixed particles, on the composition. The acetic acid particles are likely to have only a partially crystalline structure whereas the formic acid particles are likely to have an overall crystalline structure. The existence of acid in the mixed acid/ice particles prevents the ice from crystallization even at low acid concentrations (less than 10%). Mid-infrared refractive index data were derived from the different particle spectra, which can be helpful for remote sensing of such systems.     

Lamination-based rapid prototyping of microfluidic devices using flexible thermoplastic substrates

Transposing highly sensitive DNA separation methods (such as DNA sequencing with high read length or the detection of point mutations) to microchip format without loss of resolution requires fabrication of relatively long (approx. 10 cm) microchannels along with sharp injection bands. Conventional soft lithography methods, such as mold casting or hot-embossing in a press, are not convenient for fabricating long channels. We have developed a lamination-based replication technique for rapid fabrication of sealed microfluidic devices with a 10 cm long, linear separation channel. These devices are fabricated in thin cyclo-olefin copolymer (COC) plastic substrates, thus making the device flexible and capable of assuming a range of 3-D configurations. Due to the good optical properties of COC, this new family of devices combines multiple advantages of planar microfluidics and fused-silica capillaries.     

Effective on-line coupling of HPLC and flame-AAS by means of hydraulic high pressure nebulization

Summary Hydraulic high pressure nebulization is used as an effective way of on-line coupling of HPLC to flame-AAS for speciation of metal compounds in the ng range. Compared to coupling with a conventional nebulizer a signal enhancement by a factor of 7.5 (peak height) and 10.1 (peak area) for copper is obtained. Using an injected volume of 50 μL the detection limits for Cu, Fe, Ni and Cd are below 0.1 μg/mL (=5ng) and for Mg below 0.01 μg/mL (=0.5ng). The effects of HPLC flow-rate and nebulization nozzle diameter on the signal peak height have been investigated. The performance of the system is demonstrated using speciation of iron. A base-line separation of Fe(II) and Fe(III) is achieved within two minutes. Also species changes (Fe acetate to Fe citrate) can be analysed using the proposed system.     

HPLC analysis of methylxanthines in human breast milk

A sensitive and specific high-performance liquid chromatographic (HPLC) procedure is developed for simultaneously quantitating the levels of caffeine, theophylline, theobromine and paraxanthine in breast milk. The method involved the precipitation of proteins present in the milk samples with a 6% v/v perchloric acid solution containing the internal standard, proxyphylline, followed by centrifugation at 12,800 Xg for 10 minutes. The clear supernatant was then chromatographed on a C18 reversed-phase analytical column at ambient temperature using a wavelength of 272 nm. Samples were eluted from the column at a constant flow rate of 1.5 mL/min using a gradient program in which the concentration of methanol in the mobile phase varied from 0 to 16%. The mean recoveries of the methylxanthines averaged over all the concentrations examined were generally excellent and ranged from 96.3 +/- 5.4% for caffeine to 102.3 +/- 8.9% for paraxanthine. The assay precision was very good and the peaks of interest were extremely well resolved. The method is recommended for assessing the total caffeine and dimethylxanthine load to which the nursing infant is exposed in mothers ingesting typical amounts of caffeine.     

Trace analysis of chloramphenicol residues in egg powders by capillary gas chromatography-electron capture detection

Chloramphenicol (CAP) in egg powder samples was extracted with acetonitrile by sonication. After centrifugation, the supernatant was diluted with water and defatted with n-hexane, and cleanup was performed on a microcolumn of graphitized carbon black (GCB). Different silylation methods were compared for the derivatization of the analytes. Trimethylsilyl N,N-dimethylcarbamate produced stable di-TMS derivatives which were analyzed by capillary gas chromatography-electron capture detection (CGC-ECD) after splitless injection. The meta isomer of the chloramphenicol served as the internal standard for quantitation, and 80% + mean recovery was obtained in the 0.1-10 micrograms/kg (ppb) concentration range.     

Transport of organic solutes through amorphous teflon AF films

Fluorous media have great potential for selective extraction (e.g., as applied to organic synthesis). Fluorous polymer films would have significant advantages in fluorous separations. Stable films of Teflon AF 2400 were cast from solution. Films appear defect-free (SEM; AFM). Rigid aromatic solutes are transported (from chloroform solution to chloroform receiving phase) in a size-dependent manner (log permeability is proportional to -0.0067 times critical volume). Benzene's permeability is about 2 orders of magnitude higher than in comparable gas-phase experiments. The films show selectivity for fluorinated solutes in comparison to the hydrogen-containing control. Transport rates are dependent on the solvent making up the source and receiving phases. The effect of solvent is, interestingly, not due to changes in partition ratio, but rather it is due to changes in the solute diffusion coefficient in the film. Solvents plasticize the films. A less volatile compound, -COOH-terminated poly(hexafluoropropylene oxide) (4), plasticizes the films (T(g) = -40 degrees C). Permeabilities are decreased in comparison to 4-free films apparently because of decreased diffusivity of solutes. The slope of dependence of log permeability on critical volume is not changed, however.     

Syntheses and molecular structures of eta3-[(eta5-Cp*)(CO)2Fe-AsPC(SiMe3)2]M(CO)2(eta5-Cp)(M = Mo, W): the first complexes featuring eta3-arsaphosphaallyl ligands

Reaction of (eta5-Cp)(CO)2M=P=C(SiMe3)2 4a (M = Mo) and 4b (M = W) with (eta5-Cp*)(CO)2Fe-As=C(NMe2)2 5 affords the eta3-1-arsa-2-phosphaallyl complexes [(eta5-Cp*)(CO)2Fe-AsPC(SiMe3)2]M(CO)2(eta5-Cp) 6a and 6b, the molecular structures of which were determined by X-ray analyses.