Capillary liquid chromatography–microcoil 1H nuclear magnetic resonance spectroscopy and liquid chromatography–ion trap mass spectrometry for on-line structure elucidation of isoflavones in Radix astragali

Ultrasound-assisted matrix solid-phase extraction based on deep eutectic solvents and zinc oxide: Extraction and determination of six active ingredients in Ligustri Lucidi Fructus

In this study, we propose a novel strategy utilizing deep eutectic solvents (DESs) as both the extraction solvent and dispersing liquid, with nanometer zinc oxide (ZnO) serving as the adsorbent. This method incorporates ultrasound-assisted matrix solid phase dispersion (UA-MSPD) for the extraction of six active components (salidroside, echinacoside, acteoside, specnuezhenide, nuezhenoside G13, and oleanolic acid) from Ligustri Lucidi Fructus samples. The extracts were then analyzed using high-performance liquid chromatography equipped with a diode array detector. The effects of various parameters such as dispersant dosage, DESs volume, grinding time, ultrasonication duration, and eluent volume on extraction recovery were investigated and optimized using a central composite design under response surface methodology. The optimized conditions yielded detection limits ranging from 0.003 to 0.01 mg/g and relative standard deviations of 8.7% or lower. Extraction recoveries varied between 93% and 98%. The method demonstrated excellent linearity for the analytes (R2 ≥ 0.9997). The simple, green, and efficient DESs/ZnO-UA-MSPD technique proved to be rapid, accurate, and reliable for extracting and analyzing the six active ingredients in Ligustri Lucidi Fructus samples.

Metabolomic analysis reveals the valuable bioactive compounds of Ardisia elliptica

INTRODUCTION

Ardisia elliptica Thunb. (Primulaceae) is a medicinal herb that is traditionally used for the treatment of fever, diarrhoea, measles and herpes. However, there is limited information regarding the correlation of its phytoconstituents with the bioactivity. Optimisation of solvent extraction is vital for maximising retention of bioactive molecules.

OBJECTIVE

This study investigated the metabolite variations in A. elliptica leaves and the correlation with antioxidant activities.

METHODOLOGY

Total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and nitric oxide (NO) radicals scavenging assays were performed on A. elliptica leaves extracted with four different ethanol ratios (0%, 50%, 70% and absolute ethanol). The correlation of metabolites with antioxidant activities was evaluated using a nuclear magnetic resonance (NMR)-based metabolomics approach.

RESULTS

The results showed that the 50% and 70% ethanolic extracts retained the highest TPC, and the 70% ethanolic extract was the most active, exhibiting half maximal inhibitory concentration (IC₅₀ ) values of 10.18 ± 0.83 and 43.05 ± 1.69 μg/mL, respectively, in both radical scavenging assays. A total of 46 metabolites were tentatively identified, including flavonoids, benzoquinones, triterpenes and phenolic derivatives. The 50% and 70% ethanolic extracts showed similarities in metabolites content and were well discriminated from water and absolute ethanol extracts in a principal component analysis (PCA) model. Moreover, 31 metabolites were found to contribute significantly to the differentiation and antioxidant activity.

CONCLUSION

This study provides information on bioactive compounds in A. elliptica leaves, which is promising as a functional ingredient for food production or for the development of phytomedicinal products.

LC–NMR for Natural Product Analysis: A Journey from an Academic Curiosity to a Robust Analytical Tool

Liquid chromatography (LC)–nuclear magnetic resonance (NMR) combines the advantage of the outstanding separation power of liquid chromatography (LC) and the superior structural elucidating capability of nuclear magnetic resonance (NMR). NMR has proved that it is a standout detector for LC by providing maximum structural information about plant originated extracts, particularly on the isolating ability of isomeric (same molecular formula) and/or isobaric (same molecular weight) compounds as compared to other detectors. The present review provides an overview of the developmental trends and application of LC–NMR in natural product analysis. The different LC–NMR operational modes are described, and how technical improvements assist in establishing this powerful technique as an important analytical tool in the analysis of complex plant-derived compounds is also highlighted. On-flow, stop-flow and loop-storage modes, as well as the new offline mode LC–solid phase extraction (SPE)–NMR and capillary LC (capLC)–NMR configurations which avoid the ingestion of expensive deuterated solvents throughout the experiment, are mentioned. Utilization of cryogenic probe and microprobe technologies, which are the other important promising approaches for guaranteeing sensitivity, are also described. Concluding remarks and future outlooks are also discussed.

LC-NMR for Natural Products Analysis: A Journey from an Academic Curiosity to a Robust Analytical Tool

LC–NMR combines the advantage of the outstanding separation power of liquid chromatography (LC) and the superior structural elucidating capability of nuclear magnetic resonance (NMR). NMR has proved that it is a standout detector for LC by providing maximum structural information about plant originated extracts particularly in its isolating ability of isomeric (same molecular formula) and/or isobaric (same molecular weight) compounds as compared to other detectors. The present review provides an overview of the LC–NMR developmental trends and its application in natural products analysis. The different LC–NMR operational modes are described, as well as how technical improvements assist in establishing this powerful technique as an important analytical tool in the analysis of complex plant-derived compounds. On-flow, stop-flow and loop-storage modes, as well as the new offline mode LC–SPE–NMR and capLC-NMR configurations that avoid the ingestion of expensive deuterated solvents throughout the experiment are mentioned. Utilization of cryogenic probe and microprobe technologies which are the other important promising approaches for guaranteeing the sensitivity issues are also described. Concluding remarks and future outlooks are also discussed.

IN VIVO AND IN VITRO IMMUNOMODULATORY AND ANTI-INFLAMMATORY EFFECTS OF TOTAL FLAVONOIDS OF ASTRAGALUS

Background:

Astragali Radix has long been used to improve immune function in traditional Chinese medicine. However, its main active components and potential immunomodulatory or anti-inflammatory activities have not been elucidated. In the present study, the immunomodulatory and anti-inflammatory activities of total flavonoids of Astragalus (TFA) isolated from Astragali Radix were evaluated by using in vivo animal models and in vitro cell models.

Materials and Methods:

The in vivo Immunomodulatory and anti-inflammatory activities of TFA were assessed by measuring macrophage phagocytic index, delayed type hypersensitivity, serum hemolysin level and immune organ index in mice, ear edema test in mice, paw edema test in rats, vascular permeability test in mice and granuloma test in rats. The in vitro Immunomodulatory and anti-inflammatory activities of TFA were assessed by examining its effect on cytokine and mediator production in un-stimulated and LPS-stimulated murine RAW 264.7 macrophages.

Results:

The results of in vivo experiments showed that TFA enhanced macrophage phagocytic index, delayed type hypersensitivity, serum hemolysin level and immune organ index in mice, and attenuated mouse ear edema, rat paw edema, mouse vascular permeability and rat granuloma formation. The results of in vitro experiments showed that TFA stimulated the production of NO and cytokine TNF-α, IL-Ιβ, IL-6 and IFN-γ in un-stimulated RAW 264.7 macrophages, and inhibited the overproduction of these inflammatory mediators in LPS-stimulated RAW 264.7 macrophages in a dose-dependent manner without exerting cytotoxicity.

Conclusion:

These results of this study indicate that TFA have potential immunostimulatory and anti-inflammatory effects.

The importance of hyphenated techniques in the discovery of new lead compounds from nature

Nature represents an extraordinary reservoir of novel molecules and there is currently a resurgence of interest in natural products as a possible source of new lead compounds for introduction into therapeutical screening programmes. To discover new bioactive natural products, the dereplication of crude extracts performed prior to isolation work is of crucial importance for avoiding the tedious isolation of known constituents. In this respect, chemical screening strategies based on hyphenated techniques such as liquid chromatography-ultraviolet photodiode array detection, liquid chromatography-mass spectrometry, liquid chromatography tandom mass spectrometry and liquid chromatography-nuclear magnetic resonance (LC-NMR) are more and more extensively used. In the laboratory of Hostettmann's group, these analytical methods have been fully integrated into the isolation process and are used for the chemical screening of crude plant extracts, in complement with online or at-line bioassays, for rapid localisation and identification of new bioactive compounds. In this paper, possibilities and limitations of hyphenated techniques for de novo online natural product identification are discussed. As LC-NMR is playing a key role in this respect, the main part of the paper is dedicated to this technique. In particular, various ways of integrating NMR in the dereplication process are illustrated and strategies involving either direct or indirect hyphenation are presented.

Quantification of six bioactive compounds in Zhenqi Fuzheng preparation by high-performance liquid chromatography coupled with diode array detector and evaporative light scattering detector

A simple and accurate high-performance liquid chromatography (HPLC) coupled with diode array detector (DAD) and evaporative light scattering detector (ELSD) was established for the determination of six bioactive compounds in Zhenqi Fuzheng preparation (ZFP). The monitoring wavelengths were 254, 275 and 328 nm. Under the optimum conditions, good separation was achieved, and the assay was fully validated in respect of precision, repeatability and accuracy. The proposed method was successfully applied to quantify the six ingredients in 31 batches of ZFP samples and evaluate the variation by hierarchical cluster analysis (HCA), which demonstrated significant variations on the content of these compounds in the samples from different manufacturers with different preparation procedures. The developed HPLC method can be used as a valid analytical method to evaluate the intrinsic quality of this preparation.

Study of the effects of total flavonoids of Astragalus on atherosclerosis formation and potential mechanisms

Astragalus mongholicus Bunge has long been used to treat cardiovascular disease in Chinese traditional medicine. However, its mechanisms are not fully understood. In this study, we explored potential mechanisms and protective effects of total flavonoids of Astragalus (TFA) on cardiovascular disease using in vitro experiments and diet-induced atherosclerotic rabbits. We identified six components and their proportion in TFA. The animal experiments showed that TFA significantly reduced plasma levels of total cholesterol and LDL cholesterol (P < 0.05 to 0.01), increased HDL cholesterol levels (P < 0.01), and reduced the aortic fatty streak area by 43.6 to 63.6% (P < 0.01). We also found that TFA scavenged superoxide and hydroxyl radicals and this effect increased with higher TFA concentration. In in vivo experiments, TFA effectively inhibited the free radical spectrum in the ischemia-reperfusion module. In conclusion, TFA was the active component of Astragalus mongholicus Bunge, which benefits cardiovascular disease attributing to the potent antioxidant activity to improve the atherosclerosis profile.

Important roles of the hyphenated HPLC-DAD-MS-SPE-NMR technique in metabonomics

Metabolite identification is a key step for metabonomics study. A fully automated hyphenation of HPLC-diode-array detector (DAD) mass spectrometry (MS) solid phase extraction (SPE)-NMR spectroscopy (HPLC-DAD-MS-SPE-NMR) is one of the most efficient methods to determine the structure of a given unknown metabolite in a complex mixture (metabonome) and hence represents one of the most important analytical techniques for the further development of metabonomics. In this review, some recent applications of this technique in identifying novel and trace metabolites in plant extracts and drug metabolism have been discussed. Modification of this hyphenated technique, enabling multiple trappings of strong polar metabolites for biofluids, needs further development.

Bioactive flavonoids of the flowers of Butea monosperma

One new dihydrochalcone, dihydromonospermoside (7), was isolated from the flowers of Butea monosperma together with three known chalcones, butein (2), monospermoside (4) and isoliquiritigenin (8), one flavone, 7,3',4'-trihydroxyflavone (6), four flavanones, (-)-butin (1a), (-)-butrin (3a), (+)-isomonospermoside (5b) and (-)-liquiritigenin (9a), and three isoflavones, formononetin (10), afrormosin (11) and formononetin-7-O-beta-D-glucopyranoside (12). The structure of the new compound was elucidated by spectroscopic techniques whereas those of the known compounds were identified by comparisons of spectroscopic and some physical data with those of reported compounds. The absolute configurations at the 2-position of the flavanones 1a, 3a, 5b and 9a were established to be 2S, 2S, 2R and 2S, respectively, by circular dichroism spectral measurements and were confirmed by comparison of the optical rotations with those of reported values and by enzymic hydrolysis of the glucosides to the corresponding aglycones. The isolated flavonoids exhibited varying antimycobacterial activity with the chalcone 2 being the most active compound (MIC 12.5 microg/ml).

Quality evaluation of Astragali Radix using a multivariate statistical approach

The quality of 43 Astragali Radix samples collected in China and Mongolia was evaluated using multivariate statistical analysis of data obtained from liquid chromatography-ion trap-time of flight (LC-IT-TOF) mass spectrometry. The samples were classified into four characteristic groups and most of the marker compounds were identified by elemental composition data and the results of MS/MS analysis. The approach provides useful information and gives an overview of the difference between crude drugs originating from different production environments and the genetic nature of the medicinal plants. In addition, the ease with which particular marker compounds could be identified and the effectiveness of the comparison by means of multivariate statistics, such as principal component analysis (PCA), indicates that this method could be utilized for the establishment of standardization and quality control procedures for crude drugs.

Application of high-performance liquid chromatography-electrospray ionization time-of-flight mass spectrometry for analysis and quality control of Radix Astragali and its preparations

A high-performance liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry (HPLC-ESI-TOF-MS) method has been developed for qualitative and quantitative analysis of isoflavonoids and saponins, as well as for the quality control of Radix Astragali and its preparations. The selectivity, reproducibility and sensitivity are compared with HPLC with diode array detection (DAD) and evaporative light scattering detection (ELSD). Limits of detection and quantification fell in ranges of 9-40 and 23-103 ng/mL for 13 analytes with a injection of 10 microL samples, and all calibration curves showed good linear regression (r(2)>0.9938) within the test range. The assay was successfully utilized to analyze the 13 marker components in 20 samples of Radix Astragali products. The quantitative results demonstrated that samples from different localities and manufacturers showed different quality. Advantages, in comparison with conventional HPLC-DAD-ELSD, are that reliable identification of target compounds could be achieved by accurate mass measurements (<3 ppm) along with characteristic retention time, extracted ions chromatograms using a narrow mass window for quantification ensure that the chromatographic peaks are free from background or co-elutes interference, and the great enhancement in selectivity and sensitivity allows identification and quantification of low levels of constituents in complex Radix Astragali matrixes.

Metabolite profiling of mycorrhizal roots of Medicago truncatula

Metabolite profiling of soluble primary and secondary metabolites, as well as cell wall-bound phenolic compounds from roots of barrel medic (Medicago truncatula) was carried out by GC-MS, HPLC and LC-MS. These analyses revealed a number of metabolic characteristics over 56 days of symbiotic interaction with the arbuscular mycorrhizal (AM) fungus Glomus intraradices, when compared to the controls, i.e. nonmycorrhizal roots supplied with low and high amounts of phosphate. During the most active stages of overall root mycorrhization, elevated levels of certain amino acids (Glu, Asp, Asn) were observed accompanied by increases in amounts of some fatty acids (palmitic and oleic acids), indicating a mycorrhiza-specific activation of plastidial metabolism. In addition, some accumulating fungus-specific fatty acids (palmitvaccenic and vaccenic acids) were assigned that may be used as markers of fungal root colonization. Stimulation of the biosynthesis of some constitutive isoflavonoids (daidzein, ononin and malonylononin) occurred, however, only at late stages of root mycorrhization. Increase of the levels of saponins correlated AM-independently with plant growth. Only in AM roots was the accumulation of apocarotenoids (cyclohexenone and mycorradicin derivatives) observed. The structures of the unknown cyclohexenone derivatives were identified by spectroscopic methods as glucosides of blumenol C and 13-hydroxyblumenol C and their corresponding malonyl conjugates. During mycorrhization, the levels of typical cell wall-bound phenolics (e.g. 4-hydroxybenzaldehyde, vanillin, ferulic acid) did not change; however, high amounts of cell wall-bound tyrosol were exclusively detected in AM roots. Principal component analyses of nonpolar primary and secondary metabolites clearly separated AM roots from those of the controls, which was confirmed by an hierarchical cluster analysis. Circular networks of primary nonpolar metabolites showed stronger and more frequent correlations between metabolites in the mycorrhizal roots. The same trend, but to a lesser extent, was observed in nonmycorrhizal roots supplied with high amounts of phosphate. These results indicate a tighter control of primary metabolism in AM roots compared to control plants. Network correlation analyses revealed distinct clusters of amino acids and sugars/aliphatic acids with strong metabolic correlations among one another in all plants analyzed; however, mycorrhizal symbiosis reduced the cluster separation and enlarged the sugar cluster size. The amino acid clusters represent groups of metabolites with strong correlations among one another (cliques) that are differently composed in mycorrhizal and nonmycorrhizal roots. In conclusion, the present work shows for the first time that there are clear differences in development- and symbiosis-dependent primary and secondary metabolism of M. truncatula roots.

Determination of seventeen main flavonoids and saponins in the medicinal plant Huang-qi (Radix astragali) by HPLC-DAD-ELSD

A simple, rapid, and reliable method, namely high-performance liquid chromatography coupled with diode array and evaporative light scattering detectors (HPLC-DAD-ELSD), was developed to simultaneously determine twelve major flavonoids and five main saponins in different parts of the medicinal plant Huang-qi (Radix Astragali). The DAD wavelength was set at 280 nm for the UV detection of flavonoids, while the drift tube temperature was set at 105 degrees C and the nebulizing gas flow rate at 2.7 L/min for ELSD detection of saponins. The method was fully validated with respect to linearity (r2 >0.998), sensitivity, precision, and accuracy (recovery rate between 93.3 and 104.2%). The analytical results of different parts of the medicinal plant Huang-qi revealed that the levels of total flavonoids or saponins in individual parts can vary considerably and the concentration of each compound in different parts is also significantly different. The aerial parts (stems and leaves) contain even higher total contents of flavonoids (although of different kinds) than the commonly used roots of the plants. In addition, the concentration of total flavonoids and saponins in the extract of the fibrous roots was surprisingly highest among all parts of Astragalus species. All of these findings provide clear evidence and scientific support for utilization of different parts of the medicinal plant Huang-qi and also for reduction in waste of plant resources.

Implementation of real-time two-dimensional nuclear magnetic resonance spectroscopy for on-flow high-performance liquid chromatography

Directly coupled HPLC-NMR has become a powerful tool for separation and structural elucidation of unknown compounds. However, there are only a few reports on application of on-flow two-dimensional (2D) NMR in HPLC-NMR. Here we present an alternative method for recording real-time 2D-NMR spectrum (total correlation spectroscopy, TOCSY) on a commercial HPLC-NMR system. The method is based on well-established Hadamard matrix for 2D-NMR frequency encoding. In addition, a modified/improved solvent suppression approach is incorporated. This makes it possible to carry out the experiment with both polar and gradient eluents, the widely used chromatographic conditions. The method is example using a synthesized mixture of three amino acids (His, Phe and Try) and a human urine sample. The method demonstrated here may be utilized for high-throughput structural or unknown component identification and fast dynamic study in a variety of applications.

Extending the scope of NMR spectroscopy with microcoil probes

Capillary NMR (CapNMR) spectroscopy has emerged as a major breakthrough for increasing the mass-sensitivity of NMR spectroscopic analysis and enabling the combination of NMR spectroscopy with other analytical techniques. Not only is the acquisition of high-sensitivity spectra getting easier but the quality of CapNMR spectra obtained in many small-molecule applications exceeds what can be accomplished with conventional designs. This Minireview discusses current CapNMR technology and its applications for the characterization of mass-limited, small-molecule and protein samples, the rapid screening of small-molecule or protein libraries, as well as hyphenated techniques that combine CapNMR with other analytical methods.

Quality evaluation of Radix Astragali through a simultaneous determination of six major active isoflavonoids and four main saponins by high-performance liquid chromatography coupled with diode array and evaporative light scattering detectors

A method, high-performance liquid chromatography coupled with diode array and evaporative light scattering detectors (HPLC-DAD-ELSD), was developed to evaluate the quality of Radix Astragali through a simultaneous determination of six major active isoflavonoids and four main saponins. The wavelength at 280 nm was chosen to determine six isoflavonoids: calycosin-7-O-beta-D-glucoside (1), ononin (2), (6alphaR, 11alphaR)-9,10-dimethoxypterocarpan-3-O-beta-D-glucoside (3), (3R)-2'-hydroxy-3',4'-dimethoxyisoflavan-7-O-beta-D-glucoside (4), calycosin (5), and formononetin (6); and ELSD connected after DAD was employed to determine four saponins: astragaloside IV (7), astragaloside II (8), astragaloside I (9), and acetylastragaloside I (10). This assay was fully validated with respect to precision, repeatability and accuracy. The proposed method was successfully applied to quantify the ten components in eleven samples from different localities in China; significant variations were demonstrated in the content of these compounds in the samples from different areas. This simple, rapid, low-cost and reliable HPLC-DAD-ELSD method is suitable for routine quantitative analysis and quality control of traditional Chinese medicines (TCMs) consisting of bioactive multi-components with different structures such as Radix Astragali.

Comparison of analytical and semi-preparative columns for high-performance liquid chromatography–solid-phase extraction–nuclear magnetic resonance

The application of analytical and semi-preparative columns in reversed-phase liquid chromatography-solid-phase extraction-nuclear magnetic resonance (HPLC-SPE-NMR) was compared. The work was aiming at separating a higher sample amount in a single run and in this way to reduce the necessary NMR measurement time of separated compounds. Several parameters for compound separation and trapping procedures were optimised: flow rate of HPLC and make-up water pumps, choice of stationary phase cartridges and drying time. The separation and loadability of nine model compounds on analytical and semi-preparative columns was determined, as well as the focussing capacity of SH-type SPE cartridges. It was found that a semi-preparative column--or multiple peak trapping on analytical columns--gave better results than a standard 4.6mm analytical column for non-polar compounds (e.g. flavonoid aglycones, sesquiterpene lactones, non-polar terpenes, logP>2), but for polar compounds (logP<-2) did not offer any advantage over an analytical column, or was even disadvantageous. For intermediately polar compounds (-2<logP<2) this has to be investigated per compound.

Online hyphenated liquid chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry for drug metabolite and nature product analysis

Screening analysis that aims at rapidly distinguishing new molecules in the presence of a large number of known compounds becomes increasingly important in the fields of drug metabolite profiling and nature product investigation. In the past decade, online-coupled liquid chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry (LC-NMR-MS) has emerged as a powerful tool for the detection and identification of known and, more important, emerging compounds in complex clinical, pharmaceutical samples and nature product extracts, due to the complementary information provided by the two detectors for unambiguous structure elucidation. This review discusses the practical conditions under which LC-NMR-MS is suitable as a routine tool for unknown analysis, as well as the fundamental concepts and their advantage aspects. Particular attention is paid to its major operating parameters that include the instrumental configurations, working modes, NMR probe improvement and LC mobile phase selection. Finally, the recent applications of LC-NMR-MS to clinical metabolite and nature product analysis are summarized which have shown the benefit of this promising hyphenated technique.