1H and 13C NMR spectral assignments of 2′‐hydroxychalcones

Chalcones are of interest to medicinal chemists because their structures can be easily modified with various functional groups. The syntheses and biological activities of chalcones from natural sources are well known. In this study, 24 2′‐hydroxychalcones bearing methoxy substituents were synthesized, among which five are new. The NMR data for all synthesized chalcones are described for the first time. The complete assignments of the ¹H and ¹³C NMR data can be used for the identification of newly discovered and widely isolated, synthesized chalcones. Copyright © 2013 John Wiley & Sons, Ltd.     

Complete NMR data of methoxylated cis- and trans-stilbenes as well as 1,2-diphenylethanes

Resveratrol is a polyphenol isolated from many natural sources including grapes, mulberries, eucalyptus, spruce, lilies, and peanuts. The hydroxyl groups in polyphenols can be substituted with various functional groups, allowing production of multiple derivatives. NMR spectroscopy is used to identify new derivatives. Since the complete NMR data of the known derivatives can be useful for identification of the newly isolated derivatives, here, we report the synthesis of 14 methoxylated stilbenes and four 1,2-diphenylethanes and their NMR data.     

Xanthine oxidase inhibiting flavonol glycoside from Amberboa ramosa

A new flavonol glycoside (1) has been isolated from the ethyl acetate soluble fraction of Amberboa ramosa and assigned the structure 5,7,4'-trihydroxy-3,8-dimethoxylflavone 5-O-beta-D-gluco-pyranoside (1). In addition, 6,4'-dihydroxy-3,5,7-trimethoxyflavone (2), 5,7-dihydroxy-4'-methoxyflavone (3) and (23R)-5alpha-cycloart-24-ene-3beta,21,23-triol (4) have also been reported for the first time from this species. The structures were deduced on the basis of 1D and 2D NMR techniques. The compounds 1-3 displayed weak to moderate inhibition against the xanthine oxidase enzyme.     

Synthesis and complete assignment of NMR data of 20 chalcones

Chalcones, intermediates in flavonoid biosynthesis, can exhibit antibacterial, antiproliferative, and anti-inflammatory properties. Chalcones contain two benzene rings and both hydroxylated and methoxylated analogs are frequently produced by hydroxylases and O-methyltransferases in plant biosynthetic pathways. Assignments of NMR peaks in the spectra of hydroxylated and/or methoxylated chalcones can help in identifying novel chalcone derivatives isolated from natural sources by referencing these data against NMR spectra obtained from known chalcones. We report here the syntheses of 20 chalcones and complete assignments of (1)H and (13)C NMR spectra.     

Unambiguous structural characterization of hydantoin reaction products using 2D HMBC NMR spectroscopy

Data from two-dimensional (2D) NMR experiments were used to identify the reaction products resulting from the opening of pyroglutamates with isocyanates or thioisocyanates. The reaction has the potential to produce compounds that would have very similar one-dimensional proton ((1)H) or carbon-13 ((13)C) NMR spectra. Careful analysis of (1)H--(1)H COSY, (1)H--(1)H NOESY, and HMBC data, including chemical shifts and coupling constants, were used to distinguish correctly between carbamoyl-2-pyrrolidinone, hydantoin, and perhydro-1,3-diazepine-2,4-dione type structures that could result from this reaction. This work describes their preparation and subsequent identification using 2D NMR spectroscopy, and includes complete (13)C assignments of the reaction products. The 2D NMR techniques and analysis described here can be applied successfully to other synthetic reactions with the potential to produce isomeric products.     

NMR spectroscopy as a tool to investigate the degradation of aromatic compounds by a Pseudomonas putida strain

Pseudomonas putida strain KT2442, harbouring the pWW0 TOL plasmid, was grown with a number of different homologous aromatic acids as carbon sources. Small samples of liquid culture supernatant were collected and directly analysed by 2D NMR spectroscopy. In all cases similar compounds with olefinic signals were observed to accumulate. To elucidate the structures of these compounds, 2D NMR experiments with 500 and 600 MHz spectrometers equipped with a CryoProbe (Bruker BioSpin) were performed on samples obtained from a culture growing on 4‐methylbenzoate and, for ¹³C spectroscopy, on ¹³C‐labelled 4‐methylbenzoate. In all cases a 1,2‐dihydroxycyclohexa‐3,5‐diene‐carboxylate derivative was identified. The use of this technique helped us to identify easily some metabolites that were released into the solution by bacteria and to follow their secretion as a function of time. The high sensitivity of the present approach allowed a clear and rapid acquisition of spectra, notwithstanding the low concentration of the compounds. The benefits of introducing the use of NMR cryoprobes to perform metabolic pathway studies is demonstrated. Copyright © 2003 John Wiley & Sons, Ltd.     

1H and 13C NMR assignments of abietane diterpenes from Aegiphila lhotzkyana

An NMR study of one new and several known abietane diterpenes isolated from the roots of Aegiphila lhotzkyana is described. In addition to 1D NMR, several 2D shift‐correlated NMR pulse sequences (¹H–¹H‐COSY, NOESY, HMQC and HMBC) were used to establish all the structures, and unambiguously perform the ¹H and ¹³C chemical shift assignments of the new natural diterpene and three derivatives, the NMR data for which have not been reported previously. Revision of current data assignment for teuvincenone H is also suggested. Copyright © 2003 John Wiley & Sons, Ltd.     

Flavonoids from Andrographis viscosula

Phytochemical investigation of the whole plant of Andrographis viscosula has led to the isolation of three new 2'-oxygenated flavonoids, (2R)-5-hydroxy-7,2',3'-trimethoxyflavanone (1), 7,2',5'-trimethoxyflavone (2), 5,7,2',3'-tetramethoxyflavone (3), and eight known flavones, 5,7,2'-trimethoxyflavone (4), 5,7,2',4',5'-pentamethoxyflavone (5), echioidinin (6), 5,2',6'-trihydroxy-7-methoxyflavone (7), 5-hydroxy-7,2'-dimethoxyflavone (8), echioidin (9), echioidinin 5-O-glucoside (10), and 5,2',6'-trihydroxy-7-methoxyflavone 2'-O-glucoside (11). The structures of 1-11 were elucidated by physical and spectral methods, including extensive 2D NMR studies. The presence of 2'-oxygenated flavonoids is apparently restricted to Andrographis species in Acanthaceae. Therefore, 2'-oxygenated flavonoids are regarded as chemotaxonomic markers of Andrographis genus in the Acanthaceae family.     

Direct Identification of the Carbon Skeleton of Organic Compounds using Double Quantum Coherence 13C-NMR Spectroscopy. The INADEQUATE Pulse Sequence

NMR spectroscopy plays an important part in the determination of the structures of organic compounds. The parameters of importance here are the chemical shifts of the ¹H and ¹³C nuclei and the spin-spin interactions both between ¹H nuclei and between ¹H and ¹³C nuclei. Couplings between ¹³C nuclei were almost completely neglected until a few years ago, since they were extremely difficult to observe because of the low natural abundance of ¹³C. However, it is these couplings which afford information directly on the carbon-carbon connectivities in the molecule. It is now possible to use a special NMR pulse sequence to make these couplings more readily visible: the result of using this sequence is a ¹³C-NMR spectrum from which the carbon skeleton concerned can be directly read off. Two-dimensional spectra in particular are very easy to evaluate. The pulse sequence involved, which bears the somewhat puzzling name INADEQUATE, produces double-quantum coherences from which the NMR signals of the coupled carbon nuclei can be obtained. In this article the principle of double-quantum coherence is described and a number of examples for the application of the INADEQUATE pulse sequences to problems in synthetic organic chemistry, biosynthesis and natural products chemistry are presented; in addition, the possibility of applying the INADEQUATE method to other nuclei is considered.     

Structure elucidation and NMR assignments for curcuminoids from the rhizomes of Curcuma longa

Thirteen curcuminoids (1–13) were isolated from the rhizomes of Curcuma longa. Among them, 1,5‐dihydroxy‐1,7‐bis(4‐hydroxyphenyl)‐4,6‐heptadiene‐3‐one (1), 1,5‐dihydroxy‐1‐(4‐hydroxy‐3‐methoxyphenyl)‐7‐(4‐hydroxyphenyl)‐4,6‐heptadiene‐3‐one (2), 1,5‐dihydroxy‐1‐(4‐hydroxyphenyl)‐7‐(4‐hydroxy‐3‐methoxyphenyl)‐4,6‐heptadiene‐3‐one (3), and 3‐hydroxy‐1,7‐bis‐(4‐hydroxyphenyl)‐6‐heptene‐1,5‐dione (4) are new compounds, and 1‐(4‐hydroxyphenyl)‐7‐(3, 4‐dihydroxyphenyl)‐1, 6‐heptadiene‐3, 5‐dione (5) is isolated from natural sources for the first time. The structures of these compounds were elucidated by extensive spectroscopic analyses, especially 1D and 2D NMR spectroscopy. The ¹³C NMR data and complete ¹H and ¹³C NMR assignments of some known compounds are reported for the first time. In addition, the errors of ¹H and ¹³C assignments reported in the literature were corrected. Copyright © 2009 John Wiley & Sons, Ltd.     

1H and 13C NMR assignments for two oxaphenalenones bacillosporin C and D from the mangrove endophytic fungus SBE-14

The complete (1)H and (13)C NMR assignments are reported for the novel natural product Bacillosporin D together with the known compound Bacillosporin C. These compounds containing seven rings were isolated from the mangrove endophytic fungus SBE-14 from the South China Sea. 1D and 2D NMR experiments, including COSY, HMQC and HMBC were used to the determination of the structures and NMR assignments. It is proposed that 1 was biogenetically produced by transforming 2. Transforming a lactone to an anhydride is unusual in nature.     

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%.     

GIAO DFT 13C/15N chemical shifts in regioisomeric structure determination of fused pyrazoles

The combined use of two‐dimensional NMR correlation experiments and gauge including atomic orbital density functional theory in ¹³C NMR chemical shift (CS) calculations allowed reliable and simple structural determination of regioisomeric heterocyclic systems that originate from the reactions of acylquinolinones with substituted hydrazines. Moreover, the results of differential analysis between the calculated ¹⁵N NMR CSs for hypothetical structures and the experimental data of the title azaheterocyclic systems were even more advantageous with respect to ¹³C because there was no need for correlational analysis: structures of the regioisomeric compounds could be determined just by direct comparison. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies on inhibitors of skin tumor promotion. XI. Inhibitory effects of flavonoids from Scutellaria baicalensis on Epstein-Barr virus activation and their anti-tumor-promoting activities.

To search for possible anti-tumor-promoters, fourteen flavones obtained from the root of Scutellaria baicalensis were examined for their inhibitory effects on the Epstein-Barr virus early antigen (EBV-EA) activation by a short-term in vitro assay. Among these flavones, 5,7,2'-trihydroxy- and 5,7,2',3'-tetrahydroxyflavone showed remarkable inhibitory effects on the EBV-EA activation, and the effect of the latter on Raji cell cycle was also examined by flow cytometer. These two flavones exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test.     

NMR spectral assignments of a new [C--O--C] isoflavone dimer from Andira surinamensis

The phytochemical investigation of extracts from the branch wood and branch barks of Andira surinamensis yielded a novel isoflavone dimer, 4'-methoxyisoflavone-(7-O-7')-3',4'-methylenedioxyisoflavone (surinamensin), along with the triterpene lupeol and the known isoflavones 5,7-dihydroxy-4'-methoxyisoflavone (biochanin A), 5,4'-dihydroxy-7-methoxyisoflavone (prunetin), 7,3'-dihydroxy-4'-methoxyisoflavone (calycosin), and 5,7,3'-trihydroxy-4'-methoxyisoflavone (pratensein). The structure of the new isoflavone was elucidated by 1D and 2D homonuclear and heteronuclear NMR spectroscopy and by comparison with published data for closely related compounds.     

一种金属洗涤剂的NMR分析

由于精细化工行业的迅速发展,作为“工业味精”的表面活性剂,已广泛进入日化、轻工、纺织、建筑、石化、金属加工等生产领域,对其的分析也显得日益重要。表面活性剂的分析历来是比较困难的课题之一,而通过核磁共振(NMR)进行定性和定量的文献则更少[1]。本文利用NMR为多种表面活     

诱导根癌农杆菌vir区基因表达水稻代谢物的分离,鉴定和生物活性研究

从孕穗期至开花期水稻(oryza sative L. cv. lndia IR 72)的茎叶提取液中, 筛选并分离出二种能高效诱导根癌农杆菌(Agrobacterium tumfaciens) vir 区基因表达的信号分子,这两种信号分子的化学结构分别是5,7,4'-三羟基-3'-5'-二甲氧基黄酮和5,4'-二羟基-3',5'-二甲氧基-7-β-D-葡萄糖氧基黄酮.     

Structural and spectral assignments of six anthraquinone derivatives from the mangrove fungus (ZSUH-36)

A new natural product named 6,8,1'-tri-O-methyl averantin (1) has been isolated together with five known anthraquinones 1'-O-methyl averantin (2), 6,8-di-O-methyl averufin (3) averufin (4), versicolorin C (5) and 6,8-di-O-methyl averufanin (6) from a mangrove endophytic fungus ZSUH-36 collected from the South China Sea. NMR techniques including COSY, HMQC, and HMBC were used to elucidate the structures of these compounds. We report the unambiguous assignments of the (1)H and (13)C NMR spectra of the new compound 6,8,1'-tri-O-methyl averantin(1).     

Structural determination of saponins from Hedysarum polybotrys

Four saponins (1-4) were isolated from the roots of Hedysarum polybotrys Hand.-Mazz. and obtained from Hedysarum (Tourn.) L for the first time. Their structures were identified on the basis of spectroscopic data. MS, 1D and 2D NMR including HMQC, HMBC, 1H-1H COSY and NOESY permitted correct assignments of all 1H and 13C signals of 1 and 2, and the 13C NMR data of 2 were reported for the first time.     

Computational NMR spectroscopy of organoarsenicals and the natural polyarsenic compound arsenicin A

The (1)H and (13)C NMR chemical shifts and coupling constants of a series of organoarsenic compounds were calculated with DFT methods and compared with available experimental spectra. We show that non-relativistic methods successfully model the NMR spectra of these molecules; relativistic spin-orbit effects are small but appreciable for (13)C shifts, and their inclusion is beneficial. Application of the same methods of calculation to the intriguing natural polyarsenic compound arsenicin A allowed several viable alternative structures to be ruled out and thereby confirmed the previously suggested adamantane-like structure of arsenicin A. These results not only reinforce the known predictive power of DFT NMR calculations, but also open the way for the investigation of other naturally occurring molecules with unusual structures outside the scope of empirical methods.