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1.
Experimental and Theoretical Studies on the Rearrangement of 2‐Oxoazepane α,α‐Amino Acids into 2′‐Oxopiperidine β2,3,3‐Amino Acids: An Example of Intramolecular Catalysis 下载免费PDF全文
Dr. Diego Núñez‐Villanueva Dr. M. Ángeles Bonache Laura Lozano Dr. Lourdes Infantes Prof. José Elguero Prof. Ibon Alkorta Prof. M. Teresa García‐López Dr. Rosario González‐Muñiz Dr. Mercedes Martín‐Martínez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2489-2500
Enantiopure β‐amino acids represent interesting scaffolds for peptidomimetics, foldamers and bioactive compounds. However, the synthesis of highly substituted analogues is still a major challenge. Herein, we describe the spontaneous rearrangement of 4‐carboxy‐2‐oxoazepane α,α‐amino acids to lead to 2′‐oxopiperidine‐containing β2,3,3‐amino acids, upon basic or acid hydrolysis of the 2‐oxoazepane α,α‐amino acid ester. Under acidic conditions, a totally stereoselective synthetic route has been developed. The reordering process involved the spontaneous breakdown of an amide bond, which typically requires strong conditions, and the formation of a new bond leading to the six‐membered heterocycle. A quantum mechanical study was carried out to obtain insight into the remarkable ease of this rearrangement, which occurs at room temperature, either in solution or upon storage of the 4‐carboxylic acid substituted 2‐oxoazepane derivatives. This theoretical study suggests that the rearrangement process occurs through a concerted mechanism, in which the energy of the transition states can be lowered by the participation of a catalytic water molecule. Interestingly, it also suggested a role for the carboxylic acid at position 4 of the 2‐oxoazepane ring, which facilitates this rearrangement, participating directly in the intramolecular catalysis. 相似文献
2.
F. Rubio F. García H. D. Burrows A. A. C. C. Pais A. J. M. Valente M. J. Tapia J. M. García 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1788-1799
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007 相似文献
3.
On the basis of a plane-wave spectrum representation, the polarization features of a transverse quasimonochromatic non-paraxial field have been studied. A relationship has been established between the polarization characteristics in the near field and the coherence and symmetry properties of the beam in the far field. 相似文献
4.
Runqing Ou Rosario A. Gerhardt Robert J. Samuels 《Journal of Polymer Science.Polymer Physics》2003,41(8):823-841
The relationships of the structure and electrical properties of anisotropic HCl‐doped polyaniline (PANI) films cast from N,N′‐dimethylpropylene urea (DMPU) solutions and stretched to different draw ratios were studied. The anisotropic structure of the stretched PANI films was examined by X‐ray diffraction, near‐infrared wave‐guide coupling, and polarized infrared measurements. The PANI emeraldine base (EB) films cast from DMPU solutions had a single‐phase noncrystalline structure, and stretching of the films did not cause crystallization to occur. The transition moment angles of two weakly absorbing infrared bands were determined, and the Hermans' orientation functions for the PANI EB films were calculated. The PANI films were then doped with HCl, and the electrical properties were determined by impedance spectroscopy. With a specially designed test fixture, the in‐plane and through‐plane impedance was obtained. The conductivity along the stretch direction increased with orientation. The in‐plane conductivity was significantly higher than the through‐plane conductivity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 823–841, 2003 相似文献
5.
Summary A new gas chromatographic method using an automatic purge-and-trap system coupled to a GC with mass selective detection to analyze styrene at the parts-per-trillions (ng kg–1) level is described. The method shows a good sensitivity and the detection limit is 10 ng kg–1 with a relative standard deviation (RSD) of 4.7% for 164 ng kg–1 styrene in olive oil. This analytical method has been successfully applied to the analysis of styrene in extra-virgin olive oil from the European market. 相似文献
6.
A. Fernndez-Mateos E.M. Martín de la Nava R. Rabanedo Clemente R. Rubio Gonzlez M.S.J. Simmonds 《Tetrahedron》2005,61(52):12264-12274
A diastereoselective synthesis of the model insect antifeedant 29 a CDE molecular fragment of 12-ketoepoxyazadiradione has been achieved in ten steps from indenone 9 in 44% overall yield. Several of the compounds obtained along the synthesis related to model compound 29 show significant antifeedant activity against Spodoptera littoralis and Spodoptera frugiperda. 相似文献
7.
8.
I. M. Shmyt’ko A. N. Izotov N. S. Afonikova S. Vieira G. Rubio 《Physics of the Solid State》1998,40(4):687-690
The formation of polytypic modifications is observed in dislocation-free silicon single crystals under directional plastic
deformation. It is shown that the deformation-stimulated phase appears on the surface of the sample in the form of small grains
ranging from several hundred to several thousand angstroms in size. A twin structure in the individual grains is observed.
Fiz. Tverd. Tela (St. Petersburg) 40, 746–749 (April 1998) 相似文献
9.
The knowledge of the chemical forms of metals is used to assess their availability and uptake by plants, and in sediments the forms of metals determine their transport and mobility in the aquatic media. This information may be obtained by determining chemical forms of metals (speciation) or different phases in which the metals are bound, obtained by applying extraction schemes. The analytical methods used include different steps and all of them must be validated. We report here the recommendations to minimize the errors in this kind of analysis. For validation the use of Certified Reference Materials (CRMs) and the participation in interlaboratory exercises are highly recommended. 相似文献
10.
The combined effects of micellar and chemical catalysis were studied with a view to improving the features of catalytic kinetic determinations. For this purpose we chose the reaction between N,N-dimethyl-p-phenylenediamine (DPD) and N,N-dimethylaniline (DA) to form Bindschedler's Green leuco base, which is oxidized by hydrogen peroxide in a reaction catalysed by Cu(II). This reaction was found to be accelerated by anionic sodium dodecylsulphate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) micelles. Several advantages were gained in relation to the analytical features of the kinetic photometric determination of Cu(II) when the reaction was developed in the presence of micelles compared to that occurring in an aqueous medium. Such advantages include a lower detection limit, higher sensitivity, precision and solubility of DPD and DA, and substantially increased selectivity in some cases. A detailed study of the parameters which influence both reactions is reported. Some observations on the effect of SDS and DTAB on the reaction are also commented on. 相似文献