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951.
Dorothee Felix J. Schreiber K. Piers U. Horn A. Eschenmoser 《Helvetica chimica acta》1968,51(6):1461-1465
A new version of the epoxyketone → alkynone fragmentation is described. Hydrazones derived from cyclic α,β-epoxy-ketones and N-amino-aziridines decompose thermally into molecular nitrogen, an olefinic fragment and an acetylenic carbonyl compound (compare scheme 1). The reaction of phenylglyoxal with N-amino-phenyl-aziridine at room temperature produces styrene and diazo-acetophenone in high yield (compare scheme 3). 相似文献
952.
953.
954.
Galban J Cabredo S Gallarta F Sanz I Perez M Sanz J 《Analytical and bioanalytical chemistry》1996,355(3-4):406-408
Different methods for a simultaneous determination of several analytes forming volatile compounds at room temperature are described. The main steps of these methods are: continuous generation, collection in a cryogenic trap, revolatilization, measurement of the volatile compounds by Gas Phase Molecular Absorption Spectrometry and resolution by multi-wavelength methods. Several mixtures containing 2, 3 or 4 components have been studied: 1) elements forming covalent hydrides; 2) arsenic organometallic compounds forming volatile gases with a similar structure to arsine; and 3) sulphur species that can evolve volatile compounds. Under the optimum conditions obtained for each mixture, detection limits range from 0.8 ng/mL (dimethylarsinic acid) to 2 microg/mL (SCN(-)). 相似文献
955.
6-Methylthiopurines which bear a 9-NH- or a 9-NCH3-group (class A) form an [M—1]-ion with much higher abundance than do the 1-, 3-, or 7-methyl derivatives (class B). The higher stability of the [M—1]-ion in class A may be explained by ring closure to N-7. Methyl radicals are cleaved from N-, but not from S- or C-methyl groups, with the exception of the 7-methyl derivative, in which the S-CH3-group can also split off a methyl radical. The methylthio group may lose all of the following fragments: S, SH, SCH, SCH2 and SCH3. In the remaining purine skeleton, in general first the pyrimidine and subsequently the imidazole ring breaks down with elimination of HCN. 相似文献
956.
Francois Borle Felix Fehr Petr Nesvadba Albert Gossauer 《Photochemistry and photobiology》1997,65(6):949-956
On reaction with BF3 etherate, in the presence of base, bile pigments of the biliverdin and 2,3-dihydrobiliverdin type form two kinds of difluoroboron chelates. In one of them, which displays intensive photoluminescence, the boron atom is complexed through the nitrogen atoms of the dipyrrin moiety of the ligand molecule. In the second type of chelates, which have been characterized in the present work for the first time, the boron atom is complexed through the nitrogen atoms of the pyrrole and one of the terminal lactam rings. These BF2 complexes are devoid of manifest fluorescence. Their 1H-NMR spectra show clear through-space 1H-19T spin-spin couplings that served for structure elucidation. Bile pigment analogs, in which the pyrrolic HN group has been replaced by N-CH3 or by divalent heteroatoms, such as an O or S atom, form only the latter type of BF2 chelates. 相似文献
957.
The 28-membered octaazamacrocycle Me2[28]py2N6 was used as a receptor for the molecular recognition of aromatic and aliphatic carboxylate substrates. The receptor-substrate binding behaviour of (H6Me2[28]py2N6)6+ with an aliphatic (-O2C(CH2)nCO2-, n=0 to 4) and an aromatic (phthalate, isophthalate, terephthalate, 4,4'-dibenzoate, benzoate, 3- and 4-nitrobenzoate) series of carboxylate anions was evaluated by 1H NMR spectroscopy (carried out in DMSO-d6 at 300 K). Two association constants were found for most of the studied cases, except for 3- and 4-nitrobenzoate for which only K1 was determined. For oxalate, malonate, benzoate and dibenzoate anions only the beta2 constants could be obtained. The values of the first association constant cover a range from 2.86 to 3.69 (log units), and the second stepwise constant from 2.15 to 2.89 (also in log units). No special selectivity was found but the highest values were determined for adipate and the lowest for the monoprotic 3- and 4-nitrobenzoates. Single crystal X-ray structures of H6Me2[28]py2N6 6+ with terephthalate, 1, and 4,4'-dibenzoate (2) were determined showing supramolecular entities with general formula (H6Me2[28]py2N6).(substrate)2(PF6)2.4H2O. These anions are the building blocks of an extensive 3-D network of hydrogen bonds. 相似文献
958.
Ralph Hnni Felix Bigler Walter Vetter Gerhard Englert Peter Loeliger 《Helvetica chimica acta》1977,60(7):2309-2325
The Metabolism of the Retinoid Ro 10-9359. Isolation and Identification of the Major Metabolites in Human Plasma, Urine and Feces Synthesis of Three Urinary Metabolites After oral administration of therapeutic doses of the 3H-labelled aromatic retinoic acid analog (retinoid) Ro 10-9359 (ethyl all-trans-9-(4-methoxy-2,3,6-trimethyl-phenyl)-3,7-dimethyl-2,4,6,8-nonatetraenoate) to humans 75 and 15% of the 3H-dose were excreted within the first five days in the feces and the urine, respectively. Using chromatographic procedures including high pressure liquid chromatography 18 metabolites could be isolated from human urine. Their structures were elucidated by mass spectrometry and FT–1H-NMR. spectroscopy. In these urinary metabolites the tetraene side chain of the parent compound Ro 10-9359 is shortened. The radioactivity of the identified urinary metabolites accounted for about 11% of the dose. Three urinary metabolites were synthesized. The main part of the radioactivity excreted within the first five days in the feces consisted of unchanged drug (60% of the dose). A smaller (amount 15% of the dose) could not be identified. The unchanged drug and a major metabolite, the corresponding acid, were found in human plasma. In an experiment with bile-duct cannulated rats the radioactively labelled retinoid Ro 10-9359 was injected intravenously. About 70% of the 3H-dose was excreted in the bile, within the first 48 hours. The whole radioactivity of the rat bile consisted of polar metabolites. No unchanged drug could be found. After enzymatic hydrolysis of the bile conjugates three metabolites were isolated. The main metabolite (49% of the i.v. dose) was a conjugate of the corresponding acid of the parent drug, already found as free compound in human plasma. The other bile metabolites (9 and 7% of the i.v. dose) had an intact side chain, too. An enterohepatic recycling of the bile metabolites was observed in the rat. 相似文献
959.
Previously reported (J. Organomet. Chem., 246 (1983) 309) experimental data for the equilibrium constants and thermodynamic parameters of the reversible reaction 2 Rh2(CO)8 ? Rh4(CO)12 + 4 CO have been re-evaluated using more reliable values for the solubility of carbon monoxide in hexane at lower than room temperature and introducing also a fugacity vs. pressure correction for carbon monoxide. The new values are: ΔH0 = 58.6 ± 10 kJ mol?1 and ΔS0 = 305 ± 25 J mol?1 K?1 相似文献
960.
Felix Roessler Dietmar Ganzinger Siegfried Johne Emanuel Schpp Manfred Hesse 《Helvetica chimica acta》1978,61(3):1200-1206
Ruspolia hypercrateriformis M.R. : Isolation and Structure Elucidation of New Pyrrolidine Alkaloids Three new pyrrolidine alkaloids have been isolated from Ruspolia hypercrateriformis, which belongs to the plant family of Acanthaceae. The structure of the alkaloids ruspolinone ( 1 ), norruspolinone ( 2 ) and norruspoline ( 3 ) (Scheme 1) has been elucidated by means of spectroscopic data of the pure compounds and their derivatives, by chemical transformation fo 2 to 1 by methylation, by trans-formation of 3 and 2 to identical hydrogenation products, and by comparison of degradation products with synthetically prepared model compounds. 相似文献