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21.
A new method of synthesizing the alkaloid aspidospermidine (1), based on building ring E on the pyridocarbazole [ABCD] ring structure, is reported. The preparation of the pyridocarbazole framework of Aspidosperma alkaloids is a new three-step synthetic application of 2-(1,3-dithian-2-yl)indoles. A tandem conjugate addition-alkylation reaction starting from indolyldithiane (4), 3-methylenelactam 6, and EtI yields the adduct 17. Treatment of lactam 17 with DIBALH leads to formation of the naphthyridoindole 18. Compound 18 isomerizes in aqueous AcOH to yield pyridocarbazole 3. Finally, closure of ring E and subsequent reduction of the dithiane ring produces aspidospermidine. Pyridocarbazoles 2 and 10 were prepared as models. 相似文献
22.
García-Granados A López PE Melguizo E Moliz JN Parra A Simeó Y Dobado JA 《The Journal of organic chemistry》2003,68(12):4833-4844
Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory geometries. Theoretical (13)C and (1)H chemical shifts (gauge-invariant atomic orbital method at the B3LYP/6-31G*//B3LYP/6-31G* level) and (3)J(H,H) coupling constants were calculated for compounds 5-9 and 34-36, identifying the (R)- or (S)-sulfur and alpha- or beta-epoxide configurations together with 4-aza or 3-aza structures. 相似文献
23.
Verdejo B Aguilar J Doménech A Miranda C Navarro P Jiménez HR Soriano C García-España E 《Chemical communications (Cambridge, England)》2005,(24):3086-3088
L-glutamate and L-aspartate selectivity is achieved by the action of two Cu2+ metal ions rightly disposed in a cyclophane-type macrocyclic framework; electrochemical sensing of glutamate has been achieved by adsorption of the copper complexes on graphite electrodes. 相似文献
24.
Alejandro Marcó Ramón Compañó Roser Rubio Pilar Domènech Albert Palangues Miguel Maestro 《Mikrochimica acta》2002,140(1-2):131-139
Four inter-comparison exercises on organic elemental analysis were carried out between 1997 and 2001 by the Department of
Analytical Chemistry of the University of Barcelona, together with the Microanalysis Service and the Institute of the Marine
Sciences, which both belong to the CSIC in Barcelona, and the University of A Coru?a. More than sixty laboratories participated
in these exercises. Here we describe the design and characteristics of the trials, the samples and the homogeneity tests applied.
We report the results obtained for the analysis of carbon, hydrogen, nitrogen, sulphur and oxygen, their statistical analysis,
and the most relevant aspects of the technical discussion meetings.
Received December 20, 2001; accepted March 18, 2002; published online July 22, 2002 相似文献
25.
Ruiz-Medina A Ortega-Barrales P Fernández-de Córdova ML Molina-Díaz A 《Journal of AOAC International》2002,85(2):369-374
A simple, rapid, inexpensive, and automated flow-through solid-phase spectroscopic sensing device is proposed for the sequential determination of 2 vitamins: thiamine and ascorbic acid. The vitamins are concentrated on ion-exchange gels, thiamine on Sephadex SP C-25, and ascorbic acid on Sephadex QAE A-25; both solid supports are packed in 2 different flow cells. The absorbance is monitored directly on the solid phase with a double-beam spectrophotometer at 250 nm, without derivatization or additional elution. With the use of 2 carrier/self-eluting solutions (0.1 5M sodium acetate/acetic acid and 0.18M citric acid/K2HPO4) and a sample volume of 1000 microL, the sensor responds linearly in the range of 0.5-15 and 3-50 microg/mL with detection limits of 0.14 and 0.36 microg/mL for thiamine and ascorbic acid, respectively. When the method was applied to synthetic samples and pharmaceutical preparations, precise and accurate values were obtained. 相似文献
26.
Pilar Goya Juan Antonio Paez Wolfgang Pfleiderer 《Journal of heterocyclic chemistry》1984,21(3):861-864
Several pyrazino[2,3-c][1,2,6]thiadiazine 2,2-dioxide derivatives have been synthesized for the first time by condensation of suitable 4,5-diamino-1,2,6-thiadiazine 1,1-dioxides and symmetrical 1,2-dicarbonyl compounds. Structures of these compounds have been characterized by their elementary analyses, 1H-nmr and uv spectra as well as their pKa values. The most striking differences between this series and the corresponding pteridines are discussed. 相似文献
27.
A solution of a Zn-complex of recombinant mouse MT-1 isoform (Zn(7)-MT-1) was prepared and titrated with Cd(2+) ions. A method based on the coupling of capillary zone electrophoresis (CZE) with electrospray MS detection was developed for the analysis of the stoichiometry of the species formed during the titration. The method offered the possibility of the on-line removal of up to 100 mM Tris or phosphate buffer solutions that would otherwise suppress the electrospray signal. By allowing the determination of the metal stoichiometry of the complex species present in solution the method was shown to be complementary to circular dichroism and UV-VIS spectrophotometry conventionally used for similar studies. The titration of the Zn(7)-MT complex with Cd(II) showed the sequential displacement of the Zn by Cd. The unusually high stability of the Cd(6)Zn(1)-MT species was observed which suggests a structural role of the remaining Zn(II) ion. 相似文献
28.
Pilar De Miguel Nazario Martín Miguel F. Braa 《Journal of heterocyclic chemistry》1994,31(5):1235-1239
Novel tetrahydroimidazo[1,5-b]-β-carbolines derivatives 6 bearing complex basic chains as substituents on the imidic nitrogen have been prepared in a one-pot reaction. This simple experimental procedure overcomes the direct handle of isocyanates which can be favorably generated “in situ” from carbonyldiimidazole (CDI) and different amines. The stereochemistry of the novel compounds was determined by nmr experiments. 相似文献
29.
30.
Andrés Izquierdo Pilar Linares M. D. Luque de Castro Miguel Valcarcel 《Fresenius' Journal of Analytical Chemistry》1990,336(6):490-493
Summary Two fluorimetric methods are proposed for the simultaneous determination of ammonia and urea based on the reaction of the former with o-phthalaldehyde/2-mercaptoethanol and on the use of a dual injection system in which the valves are coupled in series or in parallel. An enzymatic reactor converts urea into ammonia which is determined by the same reaction. These configurations provide very similar results with a linear determination range between 0.5 and 10.0 g ml–1 and a sampling frequency of 60 h–1. The proposed methods are very tolerant to foreign species commonly found in water, as shown by applying them to samples of different origins. 相似文献