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HMBC Experiments (hmbc + experiment)
Selected AbstractsSuppressing One-Bond Correlations in HMBC Spectra: Improved Performance for the BIRD,HMBC Pulse SequenceMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2009Julien Furrer Abstract An improved version of the BIRD,HMBC experiment is proposed. In comparison to the original version, the filtering (suppression of 1JCH signals) is accomplished using a double tuned G-BIRD filter positioned in the middle of the long-range correlations evolution period. Compensation of offset dependence by replacing the rectangular 180° pulses with the broadband inversion pulses (BIPs), with superior inversion performance and improved tolerance to B1 field inhomogeneity, significantly improves the sensitivity of the original BIRD,HMBC experiment. For usual one-bond coupling constants ranges (115,180 Hz), optimal results are easily obtained by adjusting the delays, ,, of the BIRD elements to an average J value. For larger ranges (e.g. 110,260 Hz), the use of a double tuned G-BIRD filter allows excellent suppression degrees for all types of one-bond constants present in a molecule, superior to the original scheme and other purging schemes. These attributes make the improved version of the BIRD,HMBC experiment a valuable and robust tool for rapid spectral analysis and rapid checks of molecular skeletons with a minimum spectrometer time. Copyright © 2009 John Wiley & Sons, Ltd. [source] Improved multiplicity-editing of HMBC NMR spectraMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2006Andrew J. Benie Abstract A new improved multiplicity-edited HMBC experiment is introduced that leads to better J cross-talk suppression in the even (i.e. C + CH2 groups) and odd (i.e. CH + CH3 groups) subspectra. By combining data recorded with three different pulse sequences J cross-talk becomes a second-order effect in ,1J, i.e. the deviation of an actual 1J coupling constant from the value 1J0 used in setting delays , = (1J0),1/2, which is adequate for most applications. As for the original multiplicity-edited HMBC experiment, the improved experiment can be performed with a single excitation delay or implemented in a broadband version similar to broadband HMBC. Copyright © 2006 John Wiley & Sons, Ltd. [source] Multiplicity-edited broadband HMBC NMR spectraMAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2006Nils T. Nyberg Abstract A new, edited HMBC experiment is introduced that leads to two subspectra according to the number of protons attached to 13C nuclei being even or odd, i.e. one subspectrum with C + CH2 and another with CH + CH3. This experiment can be useful for resolving spectral overlap among the typically large number of peaks in HMBC spectra. It is implemented in a broadband version similar to broadband HMBC and demonstrated on prednisolone [(11,)-11,17,21-trihydroxypregna-1,4-diene-3,20-dione]. Copyright © 2006 John Wiley & Sons, Ltd. [source] The solution structure of the methylated form of the N-terminal 16-kDa domain of Escherichia coli Ada proteinPROTEIN SCIENCE, Issue 3 2006Hiroto Takinowaki N-Ada16k, the N-terminal 16-kDa domain of the Ada protein; meC38 N-Ada16k, the Cys38 methylated form of N-Ada16k; MTase, methyltransferase; HTH, helix-turn-helix; NMR, nuclear magnetic resonance; MALDI-TOF MS, matrix assisted laser desorption/ionization time of flight mass spectrometry; MNU, methylnitrosourea Abstract The N-terminal 16-kDa domain of Escherichia coli Ada protein (N-Ada16k) repairs DNA methyl phosphotriester lesions by an irreversible methyl transfer to its cysteine residue. Upon the methylation, the sequence-specific DNA binding affinity for the promoter region of the alkylation resistance genes is enhanced by 103 -fold. Then, it acts as a transcriptional regulator for the methylation damage. In this paper, we identified the methyl acceptor residue of N-Ada16k and determined the solution structure of the methylated form of N-Ada16k by using NMR and mass spectrometry. The results of a 13C-filtered 1H- 13C HMBC experiment and MALDI-TOF MS and MS/MS experiments clearly showed that the methyl acceptor residue is Cys38. The solution structure revealed that it has two distinct subdomains connected by a flexible linker loop: the methyltransferase (MTase) subdomain with the zinc,thiolate center, and the helical subdomain with a helix-turn-helix motif. Interestingly, there is no potential hydrogen bond donor around Cys38, whereas the other three cysteine residues coordinated to a zinc ion have potential donors. Hence, Cys38 could retain its inherent nucleophilicity and react with a methyl phosphotriester. Furthermore, the structure comparison shows that there is no indication of a remarkable conformational change occurring upon the methylation. This implies that the electrostatic repulsion between the negatively charged DNA and the zinc,thiolate center may avoid the contact between the MTase subdomain and the DNA in the nonmethylated form. Thus, after the Cys38 methylation, the MTase subdomain can bind the cognate DNA because the negative charge of the zinc,thiolate center is reduced. [source] The Stereostructure of Porphyra-334: An Experimental and Calculational NMR Investigation.HELVETICA CHIMICA ACTA, Issue 3 2007Evidence for an Efficient, Proton Sponge' Abstract The mycosporine-like amino acid (MAA) porphyra-334 (1) is subjected to extensive 1H- and 13C-NMR analysis as well as to density-functional-theory (DFT) calculations. All 1H- and 13C-NMR signals of 1 are assigned, as well as the resonances of prochiral proton pairs. This is achieved by 500-MHz standard COSY, HMQC, and HMBC experiments, as well as by one-dimensional (DPFGSE-NOE) and two-dimensional (NOESY) NOE experiments. Diffusion measurements (DOSY) confirm that 1 is monomeric in D2O solution. DFT Calculations yield 13C-NMR chemical shifts which are in good agreement for species 6 which is the imino N-protonated form of 1. An exceptionally high proton affinity of 265.7,kcal/mol is calculated for 1, indicating that 1 may behave as a very powerful ,proton sponge' of comparable strength as synthetic systems studied so far. Predictions of 13C-NMR chemical shifts by the ,NMRPredict' software are in agreement with the DFT data. The absolute configuration at the ring stereogenic center of 1 is concluded to be (S) from NOE data as well as from similarities with the absolute configuration (S) found in mycosporine-glycine 16. This supports the assumption that 1 is biochemically derived from 3,3- O -didehydroquinic acid (17). The data obtained question the results recently published by a different research group claiming that the configuration at the imino moiety of 1 is (Z), rather than (E) as established by the here presented study. [source] Structure elucidation and NMR assignments of two new pyrrolidinyl quinoline alkaloids from chestnut honeyMAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2009Giangiacomo Beretta Abstract The complete 1H, 13C and 15N NMR spectral assignments of two new alkaloids isolated from chestnut honey and structurally related to kynurenic acid have been made using 1-D and 2-D NMR techniques, including COSY, HMQC and HMBC experiments. The new compounds have been identified as 3-(2,-pyrrolidinyl)-kynurenic acid and its ,-lactam derivative. Copyright © 2009 John Wiley & Sons, Ltd. [source] Structural elucidation of four new furostanol saponins from Tupistra chinensis by 1D and 2D NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2009Kun Zou Abstract Four new furostanol saponins (1,4), two pairs of diastereoisomers, were isolated from methanolic extracts of Tupistra chinensis rhizomes and their structures were assigned from 1H and 13C NMR spectra, DEPT, and by 2D COSY, NOESY, HMQC, and HMBC experiments. Copyright © 2008 John Wiley & Sons, Ltd. [source] 1H and 13C NMR assignments for 6-demethylvermistatin and two penicillide derivatives from the mangrove fungus Guignardia sp. (No. 4382) from the South China SeaMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2008Xue-kui Xia Abstract One new compound 6-demethylvermistatin (1), together with two known compounds, the penicillide derivatives (2) and (3) were isolated from the mangrove fungus Guignardia sp. No. 4382 obtained from the South China Sea. Their structures were assigned using high-resolution electron ionization mass spectrometry(HREIMS), 1H and 13C NMR spectra, DEPT, and by 2D COSY, HMQC, and HMBC experiments. The absolute configuration of 1 was established by comparison of its CD with that of vermistatin. Copyright © 2008 John Wiley & Sons, Ltd. [source] Structural determination of kochiosides A,C, new steroidal glucosides from Kochia prostrata, by 1D and 2D NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2007Muhammad Imran Abstract Kochiosides A,C, three new steroidal glucosides, have been isolated from the ethyl acetate fraction of Kochia prostrata and their structures assigned from its 1H and 13C NMR spectra, DEPT and by 2D COSY, NOESY, HMQC and HMBC experiments. Copyright © 2007 John Wiley & Sons, Ltd. [source] Structural determination of silymins A and B, new pentacyclic triterpenes from Silybum marianum, by 1D and 2D NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2007Ejaz Ahmed Abstract Silymins A (1) and B (2), the new pentacyclic triterpenes, have been isolated from ethyl acetate fraction of Silybum marianum and their structures assigned from 1H and 13C NMR spectra, DEPT and by 2D COSY, NOE and HMBC experiments. Copyright © 2007 John Wiley & Sons, Ltd. [source] Aluminum(III) complexes containing O,O chelating ligandAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 8 2007Libor Dostál Abstract The stoichiometric reactions of trimethylaluminum with 2,6-(MeOCH2)2C6H3OH (LH) revealed compounds L3Al (1) and L2AlMe (2). On the other hand reaction of 1 equiv. of LH with trimethylaluminum did not lead to the formation of complex LAlMe2 (3), rather 2 together with Me3Al were observed as a result of a disproportionation of 3. Compounds 1 and 2 were characterized by elemental analysis, 1H and 13C NMR spectroscopy and in the case of 1 by X-ray diffraction. Derivative 2 underwent transmetalation with Ph3SnOH, giving LSnPh3 (4) as the result of a migration of ligand L from the aluminum to the tin atom. The identity of 4 was established by elemental analysis, 1H, 13C and 119Sn NMR spectroscopy and 1H, 119Sn HMBC experiments. The system 2 and B(C6F5)3 in a 1:1 molar ratio was shown to be active in the polymerization of propylene oxide and ,-caprolactone. Copyright © 2007 John Wiley & Sons, Ltd. [source] Studies on the Physicochemical Properties, Structure and Antitumor Activity of Polysaccharide YhPS-1 from the Root of Cordalis yanhusuo WangCHINESE JOURNAL OF CHEMISTRY, Issue 2 2006Yi-Wen Tao Abstract A polysaccharide named YhPS-1 was isolated from the root of Cordalis yanhusuo Wang and purified by means of gel-permeation chromatography and ionexchange chromatography. Its physicochemical properties, including monosaccharide composition, carbohydrate content, molecular weight and elemental composition, were determined. The structure of YhPS-1 was elucidated by chemical methods along with 1H and 13C NMR spectroscopy ways, such as including two-dimensional HMQC and HMBC experiments. These results show that YhPS-1 possesses a backbone consisting of terminal , -Glcp -(1,, , -Glcp -(1,6), , -Glcp -(1,4) and , -Glcp -(1,4,6). The bioactive assay showed that it could inhibit the growth of Sarcoma 180 and Lewis pulmonary carcinoma implanted in mice. [source] | ||||||||||