共查询到20条相似文献,搜索用时 15 毫秒
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E. M. Suleimen K. Van Hecke L. Van Meervelt Wim Deborggraeve Wim Dehaen 《Journal of Structural Chemistry》2013,54(1):189-191
The absolute configuration of 3-acetoxybetulinic acid is determined by single crystal X-ray diffraction. 相似文献
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A general method based solely on mass spectrometric techniques for the absolute configuration assignment of ortho, meta, or para isomers of acyl nitrobenzenes and derivatives is described. Instead of comparing the mass spectra of the three intact molecules
of each positional isomer and investigating each one of the many sets of positional isomers, the method generalizes the effort
by performing structural analysis on configurationally diagnostic fragment ions that are common for a given class of compounds.
These ions must therefore retain the positional information of the parent molecules and be unequivocally distinguished. Nitrobenzoyl
cations are common and stable fragment ions of most acyl nitrobenzenes and derivatives retaining the respective ortho, meta, or para configuration of the precursor molecules. The different NO2 and CO+ ring alignments profoundly influence their collision-induced dissociation and bimolecular reactivity, and the isomeric 2-,
3-, and 4-nitrobenzoyl cations are found to be unequivocally distinguished using both approaches. Absolute ortho, meta, or para positional assignment by tandem MS of every isomeric molecule of the acyl nitrobenzene class and derivatives forming detectable
amounts of any of those diagnostic nitrobenzoyl cations is, therefore, possible. The ability to perform absolute (non-comparative)
configuration assignment using such diagnostic ions is exemplified for a single test molecule of (2R)-(−)-2-methylglycidyl
4-nitrobenzoate. The general application of this absolute MS-only method for other classes of positional isomers is discussed. 相似文献
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Absolute configuration of sebiferine has been determined. 相似文献
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The common natural isomer of the allenic carotenoid fucoxanthin has the 3S,5R,6S,3′S,5′R,6′R configuration. 相似文献
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[reaction: see text] The absolute configuration of the side chain of scyphostatin (1) has been established. The chemical degradation of 1 gave 4 and 9, which correspond to the C7'-C12' and C13'-C16' fragments of the natural products, respectively. The spectroscopic data and [alpha]D values of both compounds were compared to those of authentic samples. The results show that the absolute configuration of 1 is 8'R,10'S,14'R. 相似文献
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A method involving derivatization and combined gas chromatography--mass spectrometry has been developed to separate the enantiomers of 3-hydroxyadipic acid. By combining this method with asymmetric synthesis of the same acid, it has been shown that 3-hydroxyadipic acid excreted in urine consists of at least 95% of the L-enantiomer. This finding supports the hypothesis that dicarboxylic acids are degraded by ordinary beta-oxidation, and indicates that adipic acid may be converted into succinic acid. 相似文献
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Rosane de P. Castro Carolina da S. Matos Cludia A. do Nascimento Cecília M. A. Oliveira Lucília Kato Luciano M. Lio Jos R. Sabino 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(4):m94-m96
The absolute configuration of strictosidinic acid, (2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate, was determined from its sodium chloride trihydrate, poly[[diaqua((2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐2‐ium‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate)sodium] chloride monohydrate], {[Na(C26H32N2O9)(H2O)2]Cl·H2O}n. The strictosidinic acid molecule participates in intermolecular hydrogen bonds of the O—H...O and O—H...Cl types. The solid‐state conformation was observed as a zwitterion, based on a charged pyridine N atom and a carboxylate group, the latter mediating the packing through coordination with the sodium cation. 相似文献
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Carlos A. Sanhueza Ander C. Arias Rosa L. Dorta Jesús T. Vázquez 《Tetrahedron: Asymmetry》2010,21(15):1830-1832
A series of alkyl glycosyl sulfoxides were synthesized and analyzed by NMR and CD. The study of the configuration of the sulfur atom revealed several types of spectroscopic behavior that can be used as a criterion for this purpose. The study also pointed to CD as the preferential technique, showing clear advantages over NMR methods. A general rule for determining the absolute configuration of glycosyl sulfoxides by CD is proposed. 相似文献
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Boyd DR Sharma ND Loke PL Malone JF McRoberts WC Hamilton JT 《Chemical communications (Cambridge, England)》2002,(24):3070-3071
A combination method of ozonolysis and chiral stationary phase (CSP)-GC-MS analysis has been developed to determine the enantiopurity values and absolute configurations of a range of alkaloid and coumarin hemiterpenoids derived from C- and O-prenyl epoxides. 相似文献
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Tracer experiments on Tiliacora racemosa Colebr established that tiliageine has “S” and “R” configuration at the asymmetric centres C1 and C'1 respectively. The experiments also prove that tiliageine is biosynthesised in the plants from N-methylcoclaurine. 相似文献
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Federico Berti Cristina Forzato Giada Furlan Patrizia Nitti Giuliana Pitacco Ennio Valentin Ennio Zangrando 《Tetrahedron: Asymmetry》2009,20(3):313-321
The cis- and trans-4-benzylparaconic acids and their ethyl esters were synthesized with high enantiomeric excess by hydrolysis of the corresponding diastereomeric lactonic esters using α-chymotrypsin. Thus, at low conversion values, cis- and trans-4-benzyl-5-oxo-3-tetrahydrofurancarboxylic acids were separately isolated with 99% ee and 92% ee, respectively. Both ethyl ester diastereomers were also obtained in enantiopure form. The absolute configuration of the trans-lactonic acid was assigned by 1H NMR analysis of its ester derivatives with both enantiomers of 1-(9-anthryl)-2,2,2-trifluoroethanol, while that of the cis-lactonic acid was assigned by means of X-ray analysis of a crystalline derivative. The circular dichroism curves of the products obtained are also reported. 相似文献
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