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91.
Caignan GA Deshmukh R Wilks A Zeng Y Huang HW Moënne-Loccoz P Bunce RA Eastman MA Rivera M 《Journal of the American Chemical Society》2002,124(50):14879-14892
The origin of the unusual regioselectivity of heme oxygenation, i.e. the oxidation of heme to delta-biliverdin (70%) and beta-biliverdin (30%), that is exhibited by heme oxygenase from Pseudomonas aeruginosa (pa-HO) has been studied by (1)H NMR, (13)C NMR, and resonance Raman spectroscopies. Whereas resonance Raman indicates that the heme-iron ligation in pa-HO is homologous to that observed in previously studied alpha-hydroxylating heme oxygenases, the NMR spectroscopic studies suggest that the heme in this enzyme is seated in a manner that is distinct from that observed for all other alpha-hydroxylating heme oxygenase enzymes for which a structure is known. In pa-HO, the heme is rotated in-plane approximately 110 degrees, so the delta-meso-carbon of the major orientational isomer is located within the HO-fold in the place where the alpha-hydroxylating enzymes typically place the alpha-meso-carbon. The unusual heme seating displayed by pa-HO places the heme propionates so that these groups point in the direction of the solvent-exposed heme edge and appears to originate in large part from the absence of stabilizing interactions between the polypeptide and the heme propionates, which are typically found in alpha-hydroxylating heme oxygenase enzymes. These interactions typically involve Lys-16 and Tyr-112, in Neisseriae meningitidis HO, and Lys-16 and Tyr-134, in human and rat HO-1. The corresponding residues in pa-HO are Asn-19 and Phe-117, respectively. In agreement with this hypothesis, we found that the Asn-19 Lys/Phe-117 Tyr double mutant of pa-HO exists as a mixture of molecules exhibiting two distinct heme seatings; one seating is identical to that exhibited by wild-type pa-HO, whereas the alternative seating is very similar to that typical of alpha-hydroxylating heme oxygenase enzymes and is related to the wild-type seating by approximately 110 degrees in-plane rotation of the heme. Furthermore, each of these heme seatings in the pa-HO double mutant gives rise to a subset of two heme isomeric orientations that are related to each other by 180 degrees rotation about the alpha-gamma-meso-axis. The coexistence of these molecules in solution, in the proportions suggested by the corresponding area under the peaks in the (1)H NMR spectrum, explains the unusual regioselectivity of heme oxygenation observed with the double mutant, which we found produces alpha- (55%), delta- (35%), and beta-biliverdin (10%). Alpha-biliverdin is obtained by oxidation of the heme seated similar to that of alpha-hydroxylating enzymes, whereas beta- and delta-biliverdin are formed from the oxidation of heme seated as in wild-type pa-HO. 相似文献
92.
The Diels-Alder reaction of enantiomerically pure (E)-γ-keto-α,β-unsaturated p-tolylsulphoxides 3 with cyclopentadiene give four easily separable diastereomers. The effect of several Lewis acids on the reaction was studied, finding a high endo selectivity with respect to the carbonyl group and moderate π-diastereoselectivity using BF3·Et2O as catalyst. The reactivity of compounds 3 as well as their endo selectivity are both higher than those observed for the corresponding (E)-3-sulfinylacrylates. 相似文献
93.
Chankvetadze B Lomsadze K Burjanadze N Breitkreutz J Pintore G Chessa M Bergander K Blaschke G 《Electrophoresis》2003,24(6):1083-1091
Comparative enantioseparations were performed with three neutral cyclodextrins (CDs) in capillary electrophoresis (CE). In particular, native beta-CD was compared with single component heptakis(2,3-di-O-acetyl)-beta-CD (HDA-beta-CD) and randomly acetylated beta-CD (Ac-beta-CD) with the emphasis on the enantiomer migration order. The opposite affinity of the enantiomers of several chiral analytes was observed towards native beta-CD and its acetylated derivatives. The enantiomer affinity pattern of some chiral analytes was also opposite towards the two acetylated derivatives of beta-CD. In the case of the chiral drug clenbuterol (CL) an attempt was made to evaluate the possible structural reasons of the affinity reversal using one- and two-dimensional as well as transverse rotating frame nuclear Overhauser effect spectroscopy (ROESY). Significant differences were observed between the structure of the CL complexes with beta-CD and HDA-beta-CD. 相似文献
94.
Novak P Tepes P Cindrić M Ilijas M Dragojević S Mihaljević K 《Journal of chromatography. A》2004,1033(2):299-303
Directly coupled LC-MS and LC-NMR were applied to identify and structurally characterize an acarbose degradation product A in acidic media. A comparative analysis of the stop-flow LC-NMR (1H and TOCSY) and LC-MS data provided evidence that A is structurally related to acarbose, differing from the parent compound in a number of subunits present in the molecule. Spectral analysis revealed that A was the alpha-glucosidase inhibitor amylostatin XG. Complementary information obtained from the two methods led to the structural elucidation of A which was later corroborated by high-resolution NMR spectroscopy of the isolated molecule. 相似文献
95.
Mario Di Braccio Giorgio Roma Gian Carlo Grossi Giovanni Ciarallo 《Journal of heterocyclic chemistry》1992,29(1):25-31
The reaction of 2-[(N-acyl, N-alkyl or phenyl)amino]-4H-pyrido[1,2-a]pyrimidin-4-ones 8a-g with the N,N-dimethylformamide/phosphorus oxychloride Vilsmeier reagent 1 (95°, 90 minutes) afforded 1-alkyl or phenyl-2H-dipyrido[1,2-a:2′,3′-d]pyrimidine-2,5(1H)?diones, 3-alkyl substituted or not, 10a-g . The starting compounds 8 were prepared by treating 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones N-alkyl substituted 7a,b or N-phenyl substituted 4 with excess anhydrides (130°, 7 hours) when the 2-(alkylamino) derivatives 7 were used in the reaction, compounds 8 were obtained along with very small amounts of 3-acyl-2-(alkylamino)-4H-pyrido[1,2-a]pyrimidin-4-ones 9 . 相似文献
96.
Heart rate oscillates on several different time scales and has long-term variability in the form of 1/f noise. The physiological control of heart rate is briefly reviewed, and several typical patterns of heart rate variability, in health and sickness, are described. Considered briefly are some possible dynamical mechanisms for heart rate variability. 相似文献
97.
Giovanni Appendino Giancarlo Cravotto Gian Mario Nano Giovanni Palmisano Rita Annunziata 《Helvetica chimica acta》1993,76(3):1194-1202
The reaction of 4-hydroxycoumarin and certain aliphatic aldehydes affords 1:1 or complex 2:2 adducts besides (or in place) of the expected 2:1 bis(coumarin) adducts. Reaction with heptanal, cyclohexanecarbaldehyde, and pivalaldehyde are reported as representative. The structure of the reaction products was established by spectroscopical techniques, including X-ray analysis, and their formation was mechanistically rationalized. Some of the 1:1 adducts are synthetically useful for the preparation of 3-alkyl-4-hydroxycoumarins. 相似文献
98.
Thevis M Geyer H Bahr D Schänzer W 《European journal of mass spectrometry (Chichester, England)》2005,11(4):419-427
Since January 2005, the list of prohibited substances established by the World Anti-Doping Agency prohibits the opioid agent fentanyl as well as its related drugs in professional and amateur sports. Fast, reliable and robust analytical assays are required that allow the sensitive determination of these compounds or respective metabolites in human urine, and liquid chromatography interfaced to mass spectrometry has proven to be a suitable and powerful tool for drug testing for several years. A screening and confirmation method was developed that enables the identification of fentanyl, alfentanil, remifentanil and sufentanil as well as their N-dealkylated or de-esterified metabolites utilizing solid-phase extraction of a 2 mL urine aliquot followed by LC-electrospray-MS/MS analysis. The procedure was validated in terms of recovery (95.8-104.9%), lower limit of detection (0.5 ng mL-1), specificity and interday precision (3.9-19.8%) for the four opioid drugs and the metabolic product norfentanyl. In addition, the mass spectrometric behavior of fentanyl after electrospray ionization and collision-induced dissociation was studied by synthesis and analysis of structurally related compounds, and dissociation pathways were proposed allowing the characterization of target analytes and corresponding metabolites. 相似文献
99.
The electron transfer spectra of adducts of the title metal halides with a series of ligands (nitriles, dialkylchalcogenides, phosphoryl and thiophosphoryl ligands and phosphines) have been studied. The effect of halogen substitution on the halogen metal transitions is discussed by comparing the spectra of the adducts with those of the hexahalometalates. The origin of the two ligand-metal transitions observed in most adducts is discussed, and the splitting of the metal d levels in these almost octahedral adducts is estimated. For each metal halide, the series of adducts with dialkyl chalcogenides show a linear relationship of slope one between the ligand ionisation potential and the ligand-metal charge transfer energy. The ligand optical electronegativities have been estimated. 相似文献
100.
Stíbr B Holub J Bakardjiev M Pavlík I Tok OL Císarová I Wrackmeyer B Herberhold M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(10):2239-2244
The reaction of nido-[7,8,9-PC(2)B(8)H(11)] (1) with [[CpFe(CO)(2)](2)] (Cp=eta(5)-C(5)H(5) (-)) in benzene (reflux, 3 days) gave an eta(1)-bonded complex [7-Fp-(eta(1)-nido-7,8,9,-PC(2)B(8)H(10))] (2; Fp=CpFe(CO)(2); yield 38 %). A similar reaction at elevated temperatures (xylene, reflux 24 h) gave the isomeric complex [7-Fp-(eta(1)-nido-7,9,10-PC(2)B(8)H(10))] (3; yield 28 %) together with the fully sandwiched complexes [1-Cp-closo-1,2,4,5-FePC(2)B(8)H(10)] 4 a (yield 30%) and [1-Cp-closo-1,2,4,8-FePC(2)B(8)H(10)] 4 b (yield 5%). Compounds 2 and 3 are isolable intermediates along the full eta(5)-complexation pathway of the phosphadicarbaborane cage; their heating (xylene, reflux, 24 h) leads finally to the isolation of compounds 4 a (yields 46 and 52%, respectively) and 4 b (yields 4 and 5%, respectively). Moreover, compound 3 is isolated as a side product from the heating of 2 (yield 10%). The structure of compound 4 a was determined by an X-ray structural analysis and the constitution of all compounds is consistent with the results of mass spectrometry and IR spectroscopy. Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B]-COSY, and (1)H[(11)B(selective)] magnetic resonance measurements led to complete assignments of all resonances and are in excellent agreement with the structures proposed. 相似文献