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1.
Yogesh P. Bharitkar Siddharth Shah Sudeshna Saha Anil Kumar Matoori 《Natural product research》2015,29(19):1850-1856
Phytochemical investigation of the plant Clerodendrum phlomidis Linn. F. (Lamiaceae) has now led to the isolation of two new flavonoid glycosides (1, 2) together with six known compounds identified as pectolinaringenin (3), pectolinaringenin-7-O-β-d-glucopyranoside (4), 24β-ethylcholesta-5,22E,25-triene-3β-ol (5), 24β-ethylcholesta-5,22E,25-triene-3β-O-β-D-glucopyranoside (6), (2S,3S,4R,10E)-2-[(2′R)-2′-hydroxytetracosanoylamino]-10-octadecene-1,3,4-triol (7) and andrographolide (8) mainly by spectroscopic analysis. Compounds 4 and 6–8 are reported for the first time from C. phlomidis. 相似文献
2.
Natural products often possess various spin systems consisting of a methine group directly bonded to a methyl group (e.g. –CHa–CHb(CH3)–CHc–). The methine proton Hb splits into a broadened multiplet by coupling with several vicinal protons, rendering analysis difficult of nJC–H with respect to Hb in the J‐resolved HMBC‐1. In purpose of the reliable and easy measurements of nJC–H and nJH–H in the aforesaid spin system, we have developed a new technique, named BASHD‐J‐resolved‐HMBC. This method incorporates band selective homo decoupled pulse and J‐scaling pulse into HMBC. In this method, high resolution cross peaks can be observed along the F1 axis by J‐scaling pulse, and band selective homo decoupled pulse simplified multiplet signals. Determinations of nJC–H and nJH–H of multiplet signals can easily be performed using the proposed pulse sequence. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
3.
Robert Pendrill Ole W. Sørensen Göran Widmalm 《Magnetic resonance in chemistry : MRC》2014,52(3):82-86
Site‐specific 13C isotope labeling is a useful approach that allows for the measurement of homonuclear 13C,13C coupling constants. For three site‐specifically labeled oligosaccharides, it is demonstrated that using the J‐HMBC experiment for measuring heteronuclear long‐range coupling constants is problematical for the carbons adjacent to the spin label. By incorporating either a selective inversion pulse or a constant‐time element in the pulse sequence, the interference from one‐bond 13C,13C scalar couplings is suppressed, allowing the coupling constants of interest to be measured without complications. Experimental spectra are compared with spectra of a nonlabeled compound as well as with simulated spectra. The work extends the use of the J‐HMBC experiments to site‐specifically labeled molecules, thereby increasing the number of coupling constants that can be obtained from a single preparation of a molecule. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
An efficient and facile protocol for palladacycle‐catalyzed chlorination of 2‐arylbenzoxazoles was developed. The results represent the first examples involving the palladacycle as the catalyst for such chlorination. This chlorination was not a ligand‐directed ortho‐C H activation, but an electrophilic substitution process at the para‐position of the nitrogen atom in the benzo ring of benzoxazole moiety, the regiochemistry of which had been confirmed by HMBC spectral analysis. The catalytic system could tolerate various halogen atoms, such as F, Cl and Br, affording the corresponding products in moderate to excellent yields. 相似文献
5.
The recently reported LR-HSQMBC experiment has been optimized for 1H–15N long-range heteronuclear couplings. Several previously unreported four-bond correlations, consistent with the predicted by DFT calculations (0.2–0.3 Hz 4JNH couplings), have been observed for strychnine using 2 Hz optimization of the LR-HSQMBC experiment. This experiment offers an advantage over accordion-optimized experiments such as IMPEACH and CIGAR for the observation of long-range 1H–15N correlations in that the experiment is refocused and employs a CLIP pulse sequence element to bring the long-range correlations into phase, allowing broadband X-decoupling to be employed during acquisition. 相似文献
6.
Feng-Peng Wang Dong-Lin Chen Hong-Ying Deng Qiao-Hong Chen Xiao-Yu Liu Xi-Xian Jian 《Tetrahedron》2014
We have corrected (Tetrahedron2013, 69, 5859–5866) the structures of diterpenoid alkaloids reported in the Journal of Natural Products2012, 75, 1145–1159. Our follow-up experiments compel us to present further revisions and clarifications on the diterpenoid alkaloids: 相似文献
7.
The structure of the new cycloartane glycoside cyclomacroside D, which was isolated from Astragalus macropus Bunge (Leguminosae) and is 24R-cycloartan-1α,3β,7β,24,25-pentaol 3-O-α-L-rhamnopyranoside–24-O-β-D-xylopyranoside, was proved.
Presented at the 7th International Symposium on the Chemistry of Natural Compounds (SCNC, Tashkent, Uzbekistan, October 16–18,
2007).
Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 48–50, January–February, 2009. 相似文献
8.
Jean Fotie Hilaire V. Kemami Wangun Katelyn Dreux Thomas Sommerfeld Jacob Pittman 《Magnetic resonance in chemistry : MRC》2012,50(1):68-73
Because of their extreme instability, it is generally difficult to synthesize and fully characterize open chain peroxides, also known as peroxols. In our attempt to investigate the mechanism of the Skraup–Doebner–Von Miller quinoline synthesis, we were able to obtain an unusual open chain peroxy‐quinoline, namely, 4‐(8‐ethoxy‐2,3‐dihydro‐1H‐cyclopenta[c]quinolin‐4‐yl)butane‐1‐peroxol (1), and its alcohol counterpart, namely 4‐(8‐ethoxy‐2,3‐dihydro‐1H‐cyclopenta[c]quinolin‐4‐yl)butan‐1‐ol (2) obtained as a side product during the same reaction. Although structurally similar, these two compounds appeared to display some very distinct physical and spectroscopic characteristics. This work reports detailed NMR studies and full 1H and 13 C NMR assignments for these two compounds. These assignments are based upon the analysis of the NMR spectra of these compounds including 1H, 13 C, COSY, gHSQC and gHMBC. The effect of the peroxide functional group on the chemical shift of neighboring carbons and protons was also investigated by comparing the NMR data of these two compounds. Furthermore, the effects of potential hydrogen bondings in 1, 2, and possible 1–1 dimer, 2–2 dimer and in prototypical model systems, as well as the stability of these compounds, were investigated computationally. The computed dissociation energies and NMR data support the interpretation of the experimental data. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
9.
M. Dora Carrión Luisa C. López‐Cara Mariem Chayah Duane Choquesillo‐Lazarte Miguel A. Gallo Antonio Espinosa Antonio Entrena M. Encarnación Camacho 《Magnetic resonance in chemistry : MRC》2012,50(7):515-522
The 1H and 13C NMR resonances of twenty‐seven 2,2‐dimethyl‐5‐(2‐nitrophenyl‐5‐substituted)‐2,3‐dihydro‐1,3,4‐thiadiazoles, and twenty‐seven 3‐acyl‐5‐(2‐amino‐5‐substituted)‐2,2‐dimethyl‐2,3‐dihydro‐1,3,4‐thiadiazoles were assigned completely using the concerted application of one‐dimensional and two‐dimensional experiments (DEPT, HMQC and HMBC). NOESY experiments, X‐ray crystallography and conformational analysis confirm the preferred conformation of these compounds. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
10.
Gary E. Martin R. Thomas Williamson Kirill A. Blinov Clemens G. Anklin Wolfgang Bermel 《Magnetic resonance in chemistry : MRC》2012,50(10):691-695
1,1‐ADEQUATE and the related long‐range 1,n‐ and n,1‐ADEQUATE variants were developed to provide an unequivocal means of establishing 2JCH and the equivalent of nJCH correlations where n = 3,4. Whereas the 1,1‐ and 1,n‐ADEQUATE experiments have two simultaneous evolution periods that refocus the chemical shift and afford net single quantum evolution for the carbon spins, the n,1‐variant has a single evolution period that leaves the carbon spin to be observed at the double quantum frequency. The n,1‐ADEQUATE experiment begins with an HMBC‐type nJCH magnetization transfer, which leads to inherently lower sensitivity than the 1,1‐ and 1,n‐ADEQUATE experiments that begin with a 1JCH transfer. These attributes, in tandem, serve to render the n,1‐ADEQUATE experiment less generally applicable and more difficult to interpret than the 1,n‐ADEQUATE experiment, which can in principle afford the same structural information. Unsymmetrical and generalized indirect covariance processing methods can complement and enhance the structural information encoded in combinations of experiments e.g. HSQC‐1,1‐ or ?1,n‐ADEQUATE. Another benefit is that covariance processing methods offer the possibility of mathematically combining a higher sensitivity 2D NMR spectrum with for example 1,1‐ or 1,n‐ADEQUATE to improve access to the information content of lower sensitivity congeners. The covariance spectrum also provides a significant enhancement in the F1 digital resolution. The combination of HMBC and 1,1‐ADEQUATE spectra is shown here using strychnine as a model compound to derive structural information inherent to an n,1‐ADEQUATE spectrum with higher sensitivity and in a more convenient to interpret single quantum presentation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献