Automated structure verification based on a combination of 1D (1)H NMR and 2D (1)H - (13)C HSQC spectra

A method for structure validation based on the simultaneous analysis of a 1D (1)H NMR and 2D (1)H - (13)C single-bond correlation spectrum such as HSQC or HMQC is presented here. When compared with the validation of a structure by a 1D (1)H NMR spectrum alone, the advantage of including a 2D HSQC spectrum in structure validation is that it adds not only the information of (13)C shifts, but also which proton shifts they are directly coupled to, and an indication of which methylene protons are diastereotopic. The lack of corresponding peaks in the 2D spectrum that appear in the 1D (1)H spectrum, also gives a clear picture of which protons are attached to heteroatoms. For all these benefits, combined NMR verification was expected and found by all metrics to be superior to validation by 1D (1)H NMR alone. Using multiple real-life data sets of chemical structures and the corresponding 1D and 2D data, it was possible to unambiguously identify at least 90% of the correct structures. As part of this test, challenging incorrect structures, mostly regioisomers, were also matched with each spectrum set. For these incorrect structures, the false positive rate was observed as low as 6%.     

Complete assignments of (1)H and (13)C NMR spectroscopic data for two new triterpenoid saponins from Ilex pernyi

Ilexpernoside A and ilexpernoside B, two new pentacyclic C(4)-nortriterpenoid saponins, were isolated from the leaves of Ilex pernyi Franch. Their chemical structures were determined by MS, NMR spectroscopy and chemical analysis. Complete assignments of the (1)H and (13)C NMR spectroscopic data were achieved by 1D and 2D NMR experiments (HSQC, HMBC, (1)H-(1)H COSY and NOESY).     

Complete assignments of (1)H and (13)C NMR data for two 3beta,8beta-epoxymexicanolides from the fruit of a Chinese mangrove Xylocarpus granatum

Three 3beta,8beta-epoxymexicanolides, including xyloccensin K, 6-acetoxycedrodorin and a new one named xyloccensin W, were isolated from the fruit of a Chinese mangrove Xylocarpus granatum. Their structures were determined by spectroscopic analyses. The first complete assignment of (1)H and (13)C NMR data for xyloccensin W was achieved by means of 2D NMR techniques, including (1)H-(1)H COSY, HSQC, HMBC and NOESY spectra. In addition, the confusion of (1)H and (13)C NMR data previously reported for xyloccensin K was clarified.     

First example of conformational exchange in a natural taxane enolate

A detailed NMR study and full assignments of the (1)H- and (13)C-NMR spectral data for a novel enolate taxane isolated from Taxus canadensis needles is described. The structures of two stable conformers were established using a combination of 1D and 2D NMR techniques including (1)H, (1)H-COSY, gs-HMQC, gs-HMBC, NOESY and T-ROESY. Ab initio quantum mechanical calculations were performed on the B3LYP/6-31G* level of basis set to assist the NMR findings.     

(1)H and (13)C NMR spectral data for a tricyclic derivative of a Diels-Alder adduct

A complete NMR analysis with full assignment for (1)H and (13)C NMR spectral data for 5-(acetyloxy)-3-hydroxy-9,10-dimethoxy-6-oxo-11-oxatricyclo[6.2.1.0(2,7)]undec-2-yl acetate is described. This compound was prepared by rapid hydrogenation of the unstable Diels-Alder adduct obtained from the reaction between 3,4-dimethoxyfuran and 2,5-diacetoxy-1,4-benzoquinone. Full homonuclear hydrogen coupling constants measurements and molecular mechanics calculations were performed for the determination of the relative stereochemistry.     

NMR assignments of unusual flavonoids from the kino of Eucalyptus citriodora

Two unusual flavonoids, 3,5,4',5'-tetrahydroxy-7-methoxy-6-[1-(p-hydroxy-phenyl)ethyl]flavanone (1) and 3,5,7,4',5'-pentahydroxy-6-[1-(p-hydroxy-phenyl)ethyl] flavanone (2), were isolated from the kino of Eucalyptus citriodora. Structural elucidation of the new compounds were established on the basis of spectral data, particularly by the use of 1D NMR and several 2D shift-correlated NMR pulse sequences ((1)H, (1)H-COSY, HMQC, HMBC).     

Complete 1H and 13C NMR assignments for two new monodesmoside saponins from Pentaclethra macroloba (Willd.) Kuntze

A detailed NMR study and full assignments of the 1H and 13C spectral data for two novel triterpenoid saponins isolated from the stem bark of Pentaclethra macroloba (Willd.) Kuntze are described. Their structures were established using a combination of 1D and 2D NMR techniques including 1H,1H-COSY, TOCSY, NOESY, gs-HMQC and gs-HMBC, and also electrospray ionization mass spectrometry and chemical methods. The structures were established as 3beta-O-([O-beta-D-glucopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)]-[O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->4)])-alpha-L-arabinopyranosylhederagenin (1) and 3beta-O-)[O-beta-D-glucopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)]-[O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->4)])-alpha-L-arabinopyranosyloleanolic acid (2).     

1H and 13C NMR assignments for four triterpenoid saponins from Albizziae cortex

Four triterpenoid saponins were isolated from Albizziae cortex, and a complete assignment of their (1)H and (13)C NMR spectra was carried out using 1D and 2D NMR ((1)H-(1)H COSY, HSQC, HMBC, and HSQC-TOCSY) methods. Their (1)H NMR assignments were reported for the first time and some of their (13)C NMR spectral data reported in literature were corrected.     

1H and 13C NMR signal assignment of synthetic (-)-methyl thyrsiflorin B acetate, (-)-thyrsiflorin C and several scopadulane derivatives

The (1)H and (13)C NMR signal assignment of the data of 13 scopadulane-type diterpenes is reported. It was based on one- and two- dimensional NMR techniques which included (1)H, (13)C, DEPT, HMQC and 1D NOE difference spectroscopy.     

NMR spectral assignments of isoprenylated flavanones from Sophora tonkinensis

The phytochemical investigation of extracts from the roots of Sophora tonkinensis yielded three new isoprenylated flavanones, the tonkinochromanes F (2), G (3), and H (5), along with four known compounds. Structural elucidation of the compounds were established on the basis of spectral data, particularly by the use of 1D NMR and several 2D shift-correlated NMR pulse sequences ((1)H-(1)H COSY, HSQC, HMBC, and ROESY).     

1H and 13C NMR assignments of three nitrogen containing compounds from the mangrove endophytic fungus (ZZF08)

A new natural product, named phomopsin A, 1-(meta-hydroxyphenyl)-4-hydroxy-3-isoquinolone (1), together with two known compounds cytochalasin H (2) and glucosylceramide (3), was isolated from the mangrove endophytic fungus Phomopsis sp. (ZZF08) obtained from the South China Sea coast. The structures were elucidated by 1D and 2D NMR experiments including COSY, HMQC, and HMBC. According to NMR and single-crystal X-ray diffraction, it was found that some assignments about (1)H and (13)C NMR data for cytochalasin H (2) were probably uncorrected in the previous reports. In our cytotoxicity assays, compound 1 showed moderate cytotoxicity toward KB cells with IC(50) at 28.0 microg ml(-1) and KBv200 cells with IC(50) at 16.8 microg ml(-1), and compound 2 exhibited strong cytotoxicity toward KB cells and KBv200 cells with IC(50) less than 1.25 microg ml(-1).     

Complete 1H and 13C NMR assignments of the epimeric menthane-1-carboxylic acids

Complete NMR analyses with full assignments for (1)H and (13)C NMR spectral data for both epimers of menthane-1-carboxylic acid are described. The NMR properties of the recently synthesized axial isomer had not been previously described, and through use of a variety of 1D and 2D techniques, additional information is provided for the equatorial isomer. As well as assignments of chemical shifts, homonuclear coupling constants were determined for the equatorial isomer and most of coupling constants were measured for the axial isomer.     

Structure elucidation and NMR spectral assignment of five new xanthones from the bark of Garcinia xanthochymus

Five new xanthones, namely Garcinexanthones A-E (1-5), were isolated from the barks of Garcinia xanthochymus. Their structures were elucidated by spectral analysis, primarily NMR, MS, and UV. The complete assignments of the (1)H NMR and (13)C NMR chemical shifts for the compounds were achieved by using 1D and 2D NMR techniques, including DEPT, HSQC, and HMBC NMR experiments.     

The NMR studies on two new furostanol saponins from Agave sisalana leaves

The detailed NMR studies and full assignments of the 1H and 13C spectral data for two new furostanol saponins isolated from Agave sisalana leaves are described. Their structures were established using a combination of 1D and 2D NMR techniques including 1H, 13C, 1H-1H COSY, TOCSY, HSQC, HMBC and HSQC-TOCSY, and also FAB-MS spectrometry and chemical methods. The structures were established as (25S)-26-(beta-D-glucopyranosyl)-22 xi-hydroxyfurost-12-one-3beta-yl-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->3)-O-[O-beta-D-glucopyranosyl-(1-->2)]-O-beta-D-glucopyranosyl-(1-->4)-beta-D-galacto- pyranoside (1) and (25S)-26-(beta-D-glucopyranosyl)-22xi-hydroxyfurost-5-en-12-one-3beta-yl-O-alpha-L-rhamno- pyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->3)-O-[O-beta-D-glucopyranosyl-(1-->2)]-O-beta-D-glucopyranosyl- (1-->4)-beta-D-galactopyranoside (2).     

Meso-四(4-N-苄基吡啶基)卟啉合镍(II)的溶液配位化学研究

Beer's law experiment, variable-temperature spectral experiment of UV-Vis absorption, 1H NMR, and measurement of magnetic moment were conducted for NiTMPyP in aqueous solution. It was found that Beer's law was obeyed in concentration range 8× 10-7-2×10-5.mol•dm-3.With the temperature increasing from 0 ℃ to 95 ℃, the isosbestic point appeared at 435 nm and the lowest downfield 1H NMR peak narrowed gradually and shifted to upfield. The magnetic moment is 2.07 BM in D2O at 30 ℃, but in the D2O-CD3COCD3 mixed solvent there was no evidence for the existance of paramagnetic species. These results show that NiTMPyP exists in aqueous solution as an equilibrium mixture of diamagnetic, four-coordinate nickel (Ⅱ) and paramagnetic, sir-coordinate nickel (Ⅱ) complexed by water molecules in the axial position. The thermodynamic parameters of the axial-coordinated reaction were △S?=-178.6 J•K-1•mol-1, △G298K?=-1.6 kJ•mol-1.     

Complete 1H and 13C assignments of (21R) and (21S) diastereomers of argatroban

The complete 1H and 13C NMR assignments are reported for the antithrombotic (21R)- and (21S)-argatroban by 1D and 2D NMR experiments (HSQC, HMBC, NOESY and 1H--1H COSY). Some well-resolved signals could be used for an accurate measurement of the diastereomeric composition of argatroban.     

Detailed assignments of 1H and 13C NMR spectral data of 14 cyclopentane derivatives

Detailed assignments of ¹H and ¹³C NMR spectral data for 14 cyclopentane derivatives are reported. The assignments are based on 1D ¹H and ¹³C NMR and on 2D shift‐correlated [¹H, ¹³C‐HMQC], J‐resolved and NOEDIF experiments. Copyright © 2003 John Wiley & Sons, Ltd.     

Stereochemical analysis of N-cyclohexylidene-N-(1-phenylethyl)amine derivatives

The configurational properties of a series of cyclohexylidene imines are discussed on the basis of their 1H, 13C and 15N NMR spectral data.     

3-Oxo-12alpha-hydroxyfriedelane from Maytenus gonoclada: structure elucidation by (1)H and (13)C chemical shift assignments and 2D-NMR spectroscopy

The compounds 3-oxofriedelane (1), 3beta-hydroxyfriedelane (2), 3,11-dioxofriedelane (3), 3,16-dioxofrie delane (4) and 3-oxo-12alpha-hydroxyfriedelane (5) were isolated from the hexane extract of Maytenus gonoclada Mart. (Celastraceae) leaves. Structural formula and the stereochemistry of the new pentacyclic triterpene 3-oxo-12alpha-hydroxyfriedelane (5) were established through (1)H and (13)C NMR and DEPT 135 spectral data including 2D experiments (HMBC, HMQC, COSY, and NOESY) and mass spectrometry (GC-MS).     

Complete (1)H and (13)C NMR assignments of two new trans-clerodane diterpenoids from Otostegia limbata

Two new tricyclic trans-clerodane diterpenoids trivially named as ballotenic acid A (1) and ballodiolic acid A (2) have been isolated from ethyl acetate fraction of Otostegia limbata. The structure assignments are based on (1)H and (13)C NMR spectra, 2D NMR (HMQC, HMBC, COSY, NOESY and NOE) techniques and comparison with the literature data.