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81.
Juan Francisco GonzálezElena de la Cuesta Carmen Avendaño 《Tetrahedron letters》2003,44(23):4395-4398
Addition of aldehyde dimethyl acetals (here acetaldehyde) to unisolated O-trimethylsilyl derivatives of 1-acetyl-3-arylmethylpiperazine-2,5-diones (here 2,5-dimethoxyphenyl), in the presence of TMSOTf as the catalyst, gave nearly quantitatively the corresponding N-methoxyalkyl derivatives which, under acidic treatment, gave in very good yield through a Pictet-Spengler-type reaction involving N-acyliminium cations (6S*,11aR*)-2-acetyl-6-alkyl-3,6,11,11a-tetrahydro-2H-pyrazino[1,2-b]isoquinoline-1,4-diones. Epimerization of the 11a-stereocentre was accomplished by radical bromination, spontaneous hydrobromide elimination and catalytic hydrogenation, to give the (6S*,11aS*)-isomers. We propose these compounds as precursors of tetrahydroisoquinoline antitumour antibiotics. 相似文献
82.
Freiría A Bastida R del Carmen Fernández-Fernández M Macías A Valencia L Vicente M 《Inorganic chemistry》2005,44(4):930-934
We report here the first pentanuclear Ba(II) complex of a new tri-aza, tri-oxa macrocycle with two carboxymethyl "arms" pending from two N atoms, H2L2. The crystal structure corresponds to the formula [Ba5(H0.375L2)4(ClO4)(CH3CH2OH)(H2O)2](ClO4)2.5 x 9.5H2O and reveals the presence of four molecules of the ligand surrounding five Ba(II) ions, giving rise to an unusual structure with the metal ions inside a spherical organic cavity. 相似文献
83.
Graziella Tocco Michela Begala Giovanna Delogu Carmen Picciau Gianni Podda 《Tetrahedron letters》2004,45(37):6909-6913
In the presence of catalytic amount of indium(III) chloride (10 mol %), 2,2′-dihydroxybiphenyl and bis(2-hydroxyphenyl)methane react quickly, without using any solvent, with ketones or β-keto esters possessing at least one hydrogen atom in α to the ketone-carbonyl group, to afford some new dibenzo(d,f)(1,3)dioxepines and some 12H-dibenzo(d,g)(1,3)dioxocin derivatives, respectively. 相似文献
84.
Olivares M del Carmen Thomas M López-Barajas A Requena JM García-Pérez JL Angel S Alonso C López MC 《Electrophoresis》2000,21(14):2973-2982
We have analyzed the genomic distribution and organization of the long interspersed nucleotide element (LINE) L1Tc, a nonlong terminal repeat (LTR) retrotransposon of Trypanosoma cruzi. The results indicate that the L1Tc element is dispersed along the parasite genome and that in some regions it is organized in tandem repeats. The data allowed us to define the existence of short direct-repeated sequences flanking the genomic L1Tc elements. Relevant is the finding that the LINE L1Tc is located in genomic regions rich in short interspersed nucleotide elements (SINE)-like sequences. In particular, the L1Tc element is found associated to E13-related sequences, redefined in this work and renamed RS13Tc, and to a newly described RS1Tc sequence. The RS1Tc sequence is present, per haploid genome, in about 3,200 copies. Northern blot analysis showed that the RS1Tc is being transcribed into RNAs of different sizes. The analysis of the chromosomal distribution of these elements in various strains of T. cruzi suggested that this type of clustering might be a common feature of the genome of these parasites. 相似文献
85.
Iris A. Bermejo Claudio D. Navo Jorge Castro-Lpez Ana Guerreiro Ester Jimnez-Moreno Elena M. Snchez Fernndez Fayna García-Martín Hiroshi Hinou Shin-Ichiro Nishimura Jos M. García Fernndez Carmen Ortiz Mellet Alberto Avenoza Jesús H. Busto Gonalo J. L. Bernardes Ramn Hurtado-Guerrero Jesús M. Peregrina Francisco Corzana 《Chemical science》2020,11(15):3996
The Tn antigen (GalNAc-α-1-O-Thr/Ser) is a well-known tumor-associated carbohydrate determinant. The use of glycopeptides that incorporate this structure has become a significant and promising niche of research owing to their potential use as anticancer vaccines. Herein, the conformational preferences of a glycopeptide with an unnatural Tn antigen, characterized by a threonine decorated with an sp2-iminosugar-type α-GalNAc mimic, have been studied both in solution, by combining NMR spectroscopy and molecular dynamics simulations, and in the solid state bound to an anti-mucin-1 (MUC1) antibody, by X-ray crystallography. The Tn surrogate can mimic the main conformer sampled by the natural antigen in solution and exhibits high affinity towards anti-MUC1 antibodies. Encouraged by these data, a cancer vaccine candidate based on this unnatural glycopeptide and conjugated to the carrier protein Keyhole Limpet Hemocyanin (KLH) has been prepared and tested in mice. Significantly, the experiments in vivo have proved that this vaccine elicits higher levels of specific anti-MUC1 IgG antibodies than the analog that bears the natural Tn antigen and that the elicited antibodies recognize human breast cancer cells with high selectivity. Altogether, we compile evidence to confirm that the presentation of the antigen, both in solution and in the bound state, plays a critical role in the efficacy of the designed cancer vaccines. Moreover, the outcomes derived from this vaccine prove that there is room for exploring further adjustments at the carbohydrate level that could contribute to designing more efficient cancer vaccines.An anti-cancer vaccine based on an unnatural antigen with an sp2-iminosugar fragment. 相似文献
86.
Mounir Maafi Belkacem Laassis Jean-Jacques Aaron M. Carmen Mahedero Arsenio Muñoz De La Peña Francisco Salinas 《Journal of inclusion phenomena and macrocyclic chemistry》1995,22(3):235-247
The photooxidation of Azure A and fluorescence properties of Azure A and its photoproduct have been investigated in aqueous media and in the presence of-cyclodextrin (-CD). The fluorescence intensity of the complex formed between the photoproduct and -CD was found to be three times higher than that of the uncomplexed Azure A photoproduct. A complex formation constant of 110±40 M–1 was calculated using the Benesi-Hildebrand treatment of the fluorescence emission data. Although the stoichiometry of the Azure A photoproduct: -CD complex was found to be 1: 1, it seems that the Azure A structure is only partially included. Calibration graphs were plotted for the free Azure A photoproduct and the photogenerated product included in -CD. The analytical parameters and quantification limits were determined. 相似文献
87.
Comparison of capillary electrophoresis with traditional methods to analyse bovine whey proteins 总被引:3,自引:0,他引:3
Nicki M. Kinghorn Carmen S. Norris Geoff R. Paterson Don E. Otter 《Journal of chromatography. A》1995,700(1-2):111-123
The separation of the four major whey proteins by sodium dodecyl sulphate (SDS)-capillary gel electrophoresis (CGE) is described. Whilst commercially purified whey proteins could be analysed using the recommended protocol, the more complex nature of an acid whey and a reconstituted whey protein concentrate (WPC) powder necessitated considerable refinement of the CGE sample buffer. Individual whey proteins in the acid whey and WPC samples were then also separated and quantitated using capillary zone electrophoresis, polyacrylamide gel electrophoresis (PAGE) and HPLC methods and the results were compared. The values obtained for -lactalbumin (-Lac) and β-lactoglobulin (β-Lg) were consistent throughout the various methods, although size-exclusion HPLC, SDS-PAGE and SDS-CGE could not separate the two β-Lg variants or the glycosylated form of -Lac from the β-Lg. There was considerable variation in the values for the bovine serum albumin and immunoglobulin determined by the different methods and it was concluded that none of the methods could satisfactorily quantitate all four whey proteins. 相似文献
88.
Soncini A Domene C Engelberts JJ Fowler PW Rassat A van Lenthe JH Havenith RW Jenneskens LW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(4):1257-1266
Why are some (4n+2)π systems aromatic, and some not? The ipsocentric approach to the calculation of the current density induced in a molecule by an external magnetic field predicts a four‐electron diatropic (aromatic) ring current for (4n+2)π carbocycles and a two‐electron paratropic (antiaromatic) current for (4n)π carbocycles. With the inclusion of an electronegativity parameter, an ipsocentric frontier‐orbital model also predicts the transition from delocalised currents in carbocycles to nitrogen‐localised currents in alternating azabora‐heterocycles, which rationalises the differences in (magnetic) aromaticity between these isoelectronic π‐conjugated systems. Ab initio valence‐bond calculations confirm the localisation predicted by the naïve model, and coupled‐Hartree–Fock calculations give current‐density maps that exhibit the predicted delocalised‐to‐localised/carbocycle–heterocycle transition. 相似文献
89.
The infrared andRaman spectra of the tittle compound have been recorded and an assignment for the internal vibrations of the H2S2I2O
14
4–
polyanion is proposed. The thermal behaviour was investigated using TG-, DTA-, IR- and X-ray methods; it is shown that the polyanion breaks down after the release of one mole of H2O, generating a mixture of -K2SO4 and I2O5. 相似文献
90.
Carmen Branca 《Thermochimica Acta》2005,429(2):133-141
Thermogravimetric data on the devolatilization rate of beech wood are re-examined with the aim of incorporating the effects of high heating rates (up to 108 K min−1) in the global kinetics. The mechanism consisting of three independent parallel reactions, first-order in the amount of volatiles released from pseudo-components with chief contributions from hemicellulose, cellulose and lignin, is considered first. It is found that the set of activation energies estimated by Gronli et al. [M.G. Gronli, G. Varhegyi, C. Di Blasi, Ind. Eng. Chem. Res. 41 (2002) 4201-4208] (100, 236 and 46 kJ mol−1, respectively) for one slow heating rate results in very high deviations between predicted and measured rate curves. The agreement is significantly improved by a new set of data consisting of activation energies of 147, 193 and 181 kJ mol−1, respectively. In this case, the overlap is reduced between the reaction rates of the three pseudo-components whose chemical composition is also modified. In particular, instead of a slow decomposition rate over a broad range of temperatures, the activity of the third reaction is mainly explicated along the high-temperature (tail) region of the weight loss curves. The performances of more simplified mechanisms are also evaluated. One-step mechanisms, using literature values for the kinetic constants, produce large errors on either the conversion time (activation energy of 103 kJ mol−1) or the maximum devolatilization rate (activation energy of 149 kJ mol−1). On the other hand, these parameters are well predicted by two parallel reactions, with activation energies of 147 and 149 kJ mol−1. 相似文献