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91.
Anhydrides as acylating agents in the enzymatic resolution of an intermediate of (-)-Paroxetine 总被引:2,自引:0,他引:2
de Gonzalo G Brieva R Sánchez VM Bayod M Gotor V 《The Journal of organic chemistry》2003,68(8):3333-3336
A new chemoenzymatic method for the preparation of an intermediate of (-)-Paroxetine is reported. Cyclic anhydrides are used as acylating agents in the lipase-catalyzed esterification of trans-4-(4'-fluorophenyl)-3-hydroxymethyl-N-phenyloxycarbonylpiperidine in organic solvents. The best enantioselectivities are obtained with two different lipases from Candida antarctica. These two lipases show opposite stereochemical preference in these processes, so that both enantiomers can be obtained in their optically pure forms. The (3S,4R) isomer is an intermediate for the synthesis of (-)-Paroxetine. 相似文献
92.
Laura Parejo Dr. Mahdi Chaari Sara Santiago Dr. Gonzalo Guirado Prof. Francesc Teixidor Dr. Rosario Núñez Dr. Jordi Hernando 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(1):270-280
Icosahedral metallacarboranes are θ-shaped anionic molecules in which two icosahedra share one vertex that is a metal center. The most remarkable of these compounds is the anionic cobalt-based metallacarborane [Co(C2B9H11)2]−, whose oxidation-reduction processes occur via an outer sphere electron process. This, along with its low density negative charge, makes [Co(C2B9H11)2]− very appealing to participate in electron-transfer processes. In this work, [Co(C2B9H11)2]− is tethered to a perylenediimide dye to produce the first examples of switchable luminescent molecules and materials based on metallacarboranes. In particular, the electronic communication of [Co(C2B9H11)2]− with the appended chromophore unit in these compounds can be regulated upon application of redox stimuli, which allows the reversible modulation of the emitted fluorescence. As such, they behave as electrochemically-controlled fluorescent molecular switches in solution, which surpass the performance of previous systems based on conjugates of perylendiimides with ferrocene. Remarkably, they can form gels by treatment with appropriate mixtures of organic solvents, which result from the self-assembly of the cobaltabisdicarbollide-perylendiimide conjugates into 1D nanostructures. The interplay between dye π-stacking and metallacarborane electronic and steric interactions ultimately governs the supramolecular arrangement in these materials, which for one of the compounds prepared allows preserving the luminescent behavior in the gel state. 相似文献
93.
Dieuwertje K. Modder Chad T. Palumbo Iskander Douair Rosario Scopelliti Laurent Maron Marinella Mazzanti 《Chemical science》2021,12(17):6153
The redox chemistry of uranium is dominated by single electron transfer reactions while single metal four-electron transfers remain unknown in f-element chemistry. Here we show that the oxo bridged diuranium(iii) complex [K(2.2.2-cryptand)]2[{((Me3Si)2N)3U}2(μ-O)], 1, effects the two-electron reduction of diphenylacetylene and the four-electron reduction of azobenzene through a masked U(ii) intermediate affording a stable metallacyclopropene complex of uranium(iv), [K(2.2.2-cryptand)][U(η2-C2Ph2){N(SiMe3)2}3], 3, and a bis(imido)uranium(vi) complex [K(2.2.2-cryptand)][U(NPh)2{N(SiMe3)2}3], 4, respectively. The same reactivity is observed for the previously reported U(ii) complex [K(2.2.2-cryptand)][U{N(SiMe3)2}3], 2. Computational studies indicate that the four-electron reduction of azobenzene occurs at a single U(ii) centre via two consecutive two-electron transfers and involves the formation of a U(iv) hydrazide intermediate. The isolation of the cis-hydrazide intermediate [K(2.2.2-cryptand)][U(N2Ph2){N(SiMe3)2}3], 5, corroborated the mechanism proposed for the formation of the U(vi) bis(imido) complex. The reduction of azobenzene by U(ii) provided the first example of a “clear-cut” single metal four-electron transfer in f-element chemistry.Both a masked and the actual complex [U(ii){N(SiMe3)2}3]+ effect the reduction of azobenzene to yield a U(vi) bis-imido species providing the first example of a “clear-cut” metal centred four-electron reduction in f-element chemistry. 相似文献
94.
Noelia Negreira Isaac Rodríguez Rosario Rodil Elisa Rubí Rafael Cela 《International journal of environmental analytical chemistry》2013,93(11):1174-1188
A low solvent consumption method for the determination of eight ultraviolet (UV) filters, displaying low to medium polarities, in freeze-dried samples of marine bivalves and fish is proposed. Matrix solid-phase dispersion (MSPD) and gas chromatography with mass spectrometry (GC-MS) were used as sample preparation and determination techniques, respectively. This work describes the influence of several parameters (type and amount of dispersant and clean-up sorbents, as well as elution solvent) on the yield and the selectivity of the MSPD extraction. Under optimized conditions, samples (0.5?g) were ground with 2?g of Florisil in a mortar with a pestle and transferred into a polypropylene syringe, which contained 1?g of C18 as clean-up sorbent. Analytes were eluted with 5?mL of acetonitrile. This extract was concentrated to dryness, re-constituted with 1?mL of ethyl acetate and injected in the GC-MS system without any further clean-up. The global average recoveries, measured for three different biota samples, spiked at three different levels (between 50 and 1000?ng?g?1), ranged from 80% to 101% with associated standard deviations below 10%. The inter-day precision of the method varied from 4% to 15% and the achieved LOQs (defined for a signal to noise ratio of 10) ranged from 4 to 28?ng?g?1, referred to the freeze-dried matrix. Octocrylene (OCR) was found in some samples of fish and mussels at concentrations between 15 and 20?ng?g?1, referred to dry mass. 相似文献
95.
Carolina Lipparelli Morelli José Manoel Marconcini Fabiano Vargas Pereira Rosario Elida Suman Bretas Márcia Cristina Branciforti 《Macromolecular Symposia》2012,319(1):191-195
Summary: In this study cellulose nanowhiskers were obtained from balsa wood. For this purpose, fibers of balsa wood were exposed to hydrolysis reactions for lignin and hemicellulose digestion and acquisition of nano-scale cellulose. Transmission electron microscopy (TEM) results demonstrated that the obtained cellulose nanocrystals had average length and thickness of 176 (±68 nm) and 7.5 (±2.9 nm), respectively. Infrared spectroscopy (FTIR) and wide angle x-ray diffraction (WAXD) showed that the process for extracting the nanowhiskers digested nearly all the lignin and hemicellulose from the balsa fiber and still preserved the aspect ratio and crystallinity satisfactory enough for future application as nanofillers in polymer nanocomposites. The thermogravimetric analysis (TGA) showed that the onset temperature of thermal degradation of the cellulose nanocrystals (226 °C) was higher than the onset temperature of the balsa fiber (215 °C), allowing its use in molding processes with polymers melts. 相似文献
96.
97.
Thaler F Valsasina B Baldi R Xie J Stewart A Isacchi A Kalisz HM Rusconi L 《Analytical and bioanalytical chemistry》2003,376(3):366-373
beta-Elimination of the phosphate group on phosphoserine and phosphothreonine residues and addition of an alkyldithiol is a useful tool for analysis of the phosphorylation states of proteins and peptides. We have explored the influence of several conditions on the efficiency of this PO(4)(3-) elimination reaction upon addition of propanedithiol. In addition to the described influence of different bases, the solvent composition was also found to have a major effect on the yield of the reaction. In particular, an increase in the percentage of DMSO enhances the conversion rate, whereas a higher amount of protic polar solvents, such as water or isopropanol, induces the opposite effect. We have also developed a protocol for enrichment of the modified peptides, which is based on solid-phase covalent capture/release with a dithiopyridino-resin. The procedure for beta-elimination and isolation of phosphorylated peptides by solid-phase capture/release was developed with commercially available alpha-casein. Enriched peptide fragments were characterized by MALDI-TOF mass spectrometric analysis before and after alkylation with iodoacetamide, which allowed rapid confirmation of the purposely introduced thiol moiety. Sensitivity studies, carried out in order to determine the detection limit, demonstrated that samples could be detected even in the low picomolar range by mass spectrometry. The developed solid-phase enrichment procedure based on reversible covalent binding of the modified peptides is more effective and significantly simpler than methods based on the interaction between biotin and avidin, which require additional steps such as tagging the modified peptides and work-up of the samples prior to the affinity capture step. 相似文献
98.
Conejo-García A Campos JM Entrena A Sánchez-Martín RM Gallo MA Espinosa A 《The Journal of organic chemistry》2003,68(22):8697-8699
A complete study of the conformational behavior of 4,8-diaza-3(1,4),9(4,1)-dipyridina-1,6(1,4)-dibenzenacyclodecaphan-3(1),9(1)-bis(ilium) bishexafluorophosphate is described. This study allows us to conclude that the process observed by which the different chemical shifts of the pyridinium protons show coalescence at a high-temperature 1H NMR is the rotation around the C-N bond, whereas the conformational equilibrium between the four conformers is produced at low temperature. 相似文献
99.
Mercedes Cano JosV. Heras M.Luz Gallego Josefina Perles Caridad Ruiz‐Valero Elena Pinilla M.Rosario Torres 《Helvetica chimica acta》2003,86(9):3194-3203
Two new (η3‐allyl)palladium complexes containing the ligand 3,5‐dimethyl‐4‐nitro‐1H‐pyrazole (Hdmnpz) were synthesized and characterized as [Pd(η3‐C3H5)(Hdmnpz)2]BF4 ( 1 ) and [Pd(η3‐C3H5)(Hdmnpz)2]NO3 ( 2 ). The structures of these compounds were determined by single‐crystal X‐ray diffraction to evaluate the intermolecular assembly. Each complex exhibits similar coordination behavior consistent with cationic entities comprised of two pyrazole ligands coordinated with the [Pd(η3‐C3H5)]+ fragment in an almost square‐planar coordination geometry. In 1 , the cationic entities are propagated through strong intermolecular H‐bonds formed between the pyrazole NH groups and BF ions in one‐dimensional polymer chains along the a axis. These chains are extended into two‐dimensional sheet networks via bifurcated H‐bonds. New intermolecular interactions established between NO2 and Me substituents at the pyrazole ligand of neighboring sheets give rise to a three‐dimensional network. By contrast, compound 2 presents molecular cyclic dimers formed through N? H???O H‐bonds between two NO counterions and the pyrazole NH groups of two cationic entities. The dimers are also connected to each other through C? H???O H‐bonds between the remaining O‐atom of each NO ion and the allyl CH2 H‐atom. Those interactions expand in a layer which lies parallel to the face (101). 相似文献
100.
García Martínez A Osío Barcina J Colorado Heras Mdel R Cerezo Ade F Torres Salvador Mdel R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(5):1157-1165
The syntheses of two new cyclophane hosts, 4 and 6, are described. The main difference between them is the higher degree of preorganization of 4 as a consequence of the inclusion of the 7,7-diphenylnorbornane (DPN) subunit. The inner cavity of 4 adopts a belt-shaped structure, while 6 has a twisted geometry. In the solid state, the molecules of macrocycle 6 are stacked along an axis to form nanotubular structures. Compounds 4 and 6 form two of the strongest complexes between arene cyclophanes and Ag(+) reported up to date. The silver cation is located inside the cavity of the macrocycles. The stability of 4.Ag(+) is considerably higher than that of 6.Ag(+). The additional stabilization of 4.Ag(+) is attributed to higher preorganization of macrocycle 4. DNMR experiments as well as theoretical calculations carried out with 4.Ag(+) show evidence of Ag(+)-hopping between two different binding sites inside the macrocycle. This phenomenon could be the basis for the design of molecular clocks. 相似文献