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441.
beta-D-threo- and 4-deoxy-4-amino-alpha-D-erythro-hex-2-enopyranosyl di- (n = 0) and trisaccharides (n = 1) of types A and B were synthetized by means of a reiterative, completely stereoselective glycosylation process which makes use of the D-galactal-derived allyl epoxide 1beta and D-allal-derived allyl N-nosyl aziridine 2alpha, respectively. 相似文献
442.
Crotti S Bertolini F Macchia F Pineschi M 《Chemical communications (Cambridge, England)》2008,(27):3127-3129
The first successful asymmetric transfer of rhodium-alkynyl species to symmetrical strained alkenes has been realized starting from bicyclic hydrazines and alkynylboronic esters. 相似文献
443.
We start with the universal covering space of a closed n-manifold and with a tree of fundamental domains which zips it . Our result is that, between T and , is an intermediary object, , obtained by zipping, such that each fiber of p is finite and admits a section.
相似文献
444.
D Sadhukhan C Rizzoli E Garribba CJ Gómez-García A Yahia-Ammar LJ Charbonnière S Mitra 《Dalton transactions (Cambridge, England : 2003)》2012,41(38):11565-11568
A mixed valent copper complex [Cu(II)Cu(I)(L)(μ-SCN)(μ(3)-SCN)](n) (LH = N'-((pyridin-2-yl)methylene)acetohydrazide) has been synthesized and characterized. It is a unique example of a 2D mixed valent Cu(II)-Cu(I) interlinked molecular assembly with a very unusual bridging property of the hydrazone ligand. An extraordinary in situ partial Cu(II)→ Cu(I) reduction is observed in this system at room temperature. 相似文献
445.
446.
Crevelin EJ Turatti IC Crotti AE Veneziani RC Lopes JL Lopes NP Cunha WR 《Biomedical chromatography : BMC》2006,20(8):827-830
In this work we describe the identification of the biologically active triterpenes and sterols present in the hexane extracts of six species of Miconia using gas chromatography. The main compounds present in these extracts are beta-amyrin, alpha-amyrin, and beta-sitosterol. The technique employed herein is shown to be a valuable and rapid tool for determining biologically active triterpenes and sterols present in non-polar extracts. 相似文献
447.
Stefano Crotti 《Tetrahedron letters》2010,51(17):2284-5155
The ring opening of [2.2.2]-acylnitroso cycloadducts was obtained for the first time by means of a cationic rearrangement promoted by Cu(OTf)2-PPh3 under homogeneous and polymer-supported conditions. 相似文献
448.
Gas‐phase fragmentation of γ‐lactone derivatives by electrospray ionization tandem mass spectrometry
Antonio E. M. Crotti Erika S. Bronze‐Uhle Paulo G. B. D. Nascimento Paulo M. Donate Sérgio E. Galembeck Ricardo Vessecchi Norberto P. Lopes 《Journal of mass spectrometry : JMS》2009,44(12):1733-1741
Fragmentation reactions of β‐hydroxymethyl‐, β‐acetoxymethyl‐ and β‐benzyloxymethyl‐butenolides and the corresponding γ‐butyrolactones were investigated by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) using collision‐induced dissociation (CID). This study revealed that loss of H2O [M + H ?18]+ is the main fragmentation process for β‐hydroxymethylbutenolide (1) and β‐hydroxymethyl‐γ‐butyrolactone (2). Loss of ketene ([M + H ?42]+) is the major fragmentation process for protonated β‐acetoxymethyl‐γ‐butyrolactone (4), but not for β‐acetoxymethylbutenolide (3). The benzyl cation (m/z 91) is the major ion in the ESI‐MS/MS spectra of β‐benzyloxymethylbutenolide (5) and β‐benzyloxymethyl‐γ‐butyrolactone (6). The different side chain at the β‐position and the double bond presence afforded some product ions that can be important for the structural identification of each compound. The energetic aspects involved in the protonation and gas‐phase fragmentation processes were interpreted on the basis of thermochemical data obtained by computational quantum chemistry. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
449.
Sébastien Neukirch Joël Frelat Alain Goriely Corrado Maurini 《Journal of sound and vibration》2012,331(3):704-720
The small-amplitude in-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible, shearable, planar Kirchhoff elastic rod under large displacements and rotations, and the vibration frequencies are computed both analytically and numerically as a function of the loading. Of particular interest is the variation of mode frequencies as the load is increased through the buckling threshold. While for some modes there are no qualitative changes in the mode frequencies, other frequencies experience rapid variations after the buckling threshold, the thinner the rod, the more abrupt the variations. Eventually, a mismatch for half of the frequencies at buckling arises between the zero thickness limit of the extensible model and the inextensible model. 相似文献