Combination of matrix solid-phase dispersion extraction and direct on-line liquid chromatography-nuclear magnetic resonance spectroscopy-tandem mass spectrometry as a new efficient approach for the rapid screening of natural products: application to the total asterosaponin fraction of the starfish Asterias rubens

Mass spectrometry analysis of saponins

Saponins are amphiphilic molecules of pharmaceutical interest and most of their biological activities (i.e., cytotoxic, hemolytic, fungicide, etc.) are associated to their membranolytic properties. These molecules are secondary metabolites present in numerous plants and in some marine animals, such as sea cucumbers and starfishes. Structurally, all saponins correspond to the combination of a hydrophilic glycan, consisting of sugar chain(s), linked to a hydrophobic triterpenoidic or steroidic aglycone, named the sapogenin. Saponins present a high structural diversity and their structural characterization remains extremely challenging. Ideally, saponin structures are best established using nuclear magnetic resonance experiments conducted on isolated molecules. However, the extreme structural diversity of saponins makes them challenging from a structural analysis point of view since, most of the time, saponin extracts consist in a huge number of congeners presenting only subtle structural differences. In the present review, we wish to offer an overview of the literature related to the development of mass spectrometry for the study of saponins. This review will demonstrate that most of the past and current mass spectrometry methods, including electron, electrospray and matrix-assisted laser desorption/ionization ionizations, gas/liquid chromatography coupled to (tandem) mass spectrometry, collision-induced dissociation including MS³ experiments, multiple reaction monitoring based quantification, ion mobility experiments, and so forth, have been used for saponin investigations with great success on enriched extracts but also directly on tissues using imaging methods.

Biochemical metabolomic profiling of the Crown-of-Thorns Starfish (Acanthaster): New insight into its biology for improved pest management

The Crown-of-Thorns Starfish (COTS), Acanthaster species, is a voracious coral predator that destroys coral reefs when in outbreak status. The baseline metabolite and lipid biomolecules of 10 COTS tissues, including eggs from gravid females, were investigated in this study to provide insight into their biology and identify avenues for control. Targeted and untargeted metabolite- and lipidomics-based mass spectrometry approaches were used to obtain tissue-specific metabolite and lipid profiles. Across all COTS tissues, 410 metabolites and 367 lipids were identified. Most abundant were amino acids and peptides (18.7%) and wax esters (17%). There were 262 metabolites and 192 lipids identified in COTS eggs. Wax esters were more abundant in the eggs (30%) followed by triacylglycerols (TG), amino acids, and peptides. The diversity of asterosaponins in eggs (34) was higher than in tissues (2). Several asterosaponins known to modulate sperm acrosome reaction were putatively identified, including glycoside B, asterosaponin-4 (Co-Aris III), and regularoside B (asterosaponin A). The saponins saponin A, thornasteroside A, hillaside B, and non-saponins dictyol J and axinellamine B which have been shown to possess defensive properties, were found in abundance in gonads, skin, and radial nerve tissues. Inosine and 2-hexyldecanoic acid are the most abundant metabolites in tissues and eggs. As a secondary metabolite of purine degradation, inosine plays an important role in purine biosynthesis, while 2-hexyldecanoic acid is known to suppress side-chain crystallization during the synthesis of amphiphilic macromolecules (i.e., phospholipids). These significant spatial changes in metabolite, lipid, and asterosaponin profiles enabled unique insights into key biological tissue-specific processes that could be manipulated to better control COTS populations. Our findings highlight COTS as a novel source of molecules with therapeutic and cosmetic properties (ceramides, sphingolipids, carnosine, and inosine). These outcomes will be highly relevant for the development of strategies for COTS management including chemotaxis-based biocontrol and exploitation of COTS carcasses for the extraction of commercial molecules.

Application of MS-Based Metabolomic Approaches in Analysis of Starfish and Sea Cucumber Bioactive Compounds

Today, marine natural products are considered one of the main sources of compounds for drug development. Starfish and sea cucumbers are potential sources of natural products of pharmaceutical interest. Among their metabolites, polar steroids, triterpene glycosides, and polar lipids have attracted a great deal of attention; however, studying these compounds by conventional methods is challenging. The application of modern MS-based approaches can help to obtain valuable information about such compounds. This review provides an up-to-date overview of MS-based applications for starfish and sea cucumber bioactive compounds analysis. While describing most characteristic features of MS-based approaches in the context of starfish and sea cucumber metabolites, including sample preparation and MS analysis steps, the present paper mainly focuses on the application of MS-based metabolic profiling of polar steroid compounds, triterpene glycosides, and lipids. The application of MS in metabolomics studies is also outlined.

Bioactive Phenolic Compounds from Primula veris L.: Influence of the Extraction Conditions and Purification

Our experiments may help to answer the question of whether cowslip (Primula veris L.) is a rich source of bioactive substances that can be obtained by efficient extraction with potential use as a food additive. A hypothesis assumed that the type of solvent used for plant extraction and the individual morphological parts of Primula veris L. used for the preparation of herbal extracts will have key impacts on the efficiency of the extraction of bioactive compounds, and thus, the health-promoting quality of plant concentrates produced. Most analysis of such polyphenolic compound contents in extracts from Primula veris L. has been performed by using chromatography methods such as ultra-performance reverse-phase liquid chromatography (UPLC-PDA-MS/MS). Experiments demonstrated that the most effective extraction agent for fresh study material was water at 100 °C, whereas for dried material it was 70% ethanol. The richest sources of polyphenolic compounds were found in cowslip primrose flowers and leaves. The aqueous and ethanol extracts from Primula veris L. were characterized by a quantitatively rich profile of polyphenolic substances, and a high antioxidative potential. Selective extraction with the use of mild conditions and neutral solvents is the first step to obtaining preparations from cowslip primrose with a high content of bioactive substances.

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.

Asterosaponins: Structures, Taxonomic Distribution, Biogenesis and Biological Activities

Asterosaponins are a class of steroid oligoglycosides isolated from starfish with characteristic structures and diverse biological activities. In this review, we have attempted to combine the most important data concerning asterosaponins and give a list of these secondary metabolites with their structural peculiarities. The purpose of this review is to provide a brief but as complete as possible principal information about their chemical structures, taxonomic distribution in the marine environment, distribution in different geographical areas and depths, some properties, biological activities, and functions. Some other rare steroid metabolites from starfish, closely related in structures and probably biogenesis to asterosaponins, are also discussed.

The integration of LC-MS and NMR for the analysis of low molecular weight trace analytes in complex matrices

This review discusses the integration of liquid chromatography (LC), mass spectrometry (MS), and nuclear magnetic resonance (NMR) in the comprehensive analysis of small molecules from complex matrices. We first discuss the steps taken toward making the three technologies compatible, so as to create an efficient analytical platform. The development of online LC-MS-NMR, highlighted by successful applications in the profiling of highly concentrated analytes (LODs 10 μg) is discussed next. This is followed by a detailed overview of the alternative approaches that have been developed to overcome the challenges associated with online LC-MS-NMR that primarily stem from the inherently low sensitivity of NMR. These alternative approaches include the use of stop-flow LC-MS-NMR, loop collection of LC peaks, LC-MS-SPE-NMR, and offline NMR. The potential and limitations of all these approaches is discussed in the context of applications in various fields, including metabolomics and natural product discovery.

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.

Structural Characterization of Polar Steroid Compounds of the Far Eastern Starfish Lethasterias fusca by Nanoflow Liquid Chromatography Coupled to Quadrupole Time-of-Flight Tandem Mass Spectrometry

Nanoflow liquid chromatography coupled with a captive spray ionization time-of-flight tandem mass spectrometer (nLC/CSI-QTOF-MS/MS) was used in the structural determination of polar steroid compounds of starfish Lethasterias fusca. A total of 207 compounds including 106 asterosaponins, 81 glycosides of polyhydroxysteroids, and 14 polyhydroxylated steroids were detected and characterized by MS and MS/MS. Twenty compounds among them were unambiguously identified using authentic standard compounds, isolated earlier from this and other starfish species. The other compounds were tentatively characterized by accurate mass measurement and comparing retention times and characteristic MS/MS fragmentation patterns with reference standards. Moreover, fragmentation behaviors of a series of pure standards of starfish polar steroids and polyhydroxysteroid compounds detected in L. fusca have been extensively investigated and characteristic fragmentation pathways were described and used for the characterization of unknown compounds.

Inter- and intra-organ spatial distributions of sea star saponins by MALDI imaging

Saponins are secondary metabolites that are abundant and diversified in echinoderms. Mass spectrometry is increasingly used not only to identify saponin congeners within animal extracts but also to decipher the structure/biological activity relationships of these molecules by determining their inter-organ and inter-individual variability. The usual method requires extensive purification procedures to prepare saponin extracts compatible with mass spectrometry analysis. Here, we selected the sea star Asterias rubens as a model animal to prove that direct analysis of saponins can be performed on tissue sections. We also demonstrated that carboxymethyl cellulose can be used as an embedding medium to facilitate the cryosectioning procedure. Matrix-assisted laser desorption/ionization (MALDI) imaging was also revealed to afford interesting data on the distribution of saponin molecules within the tissues. We indeed highlight that saponins are located not only inside the body wall of the animals but also within the mucus layer that probably protects the animal against external aggressions. Graphical Abstract Saponins are the most abundant secondary metabolites in sea stars. They should therefore participate in important biological activities. Here, MALDI imaging is presented as a powerful method to determine the spatial distribution of saponins within the animal tissues. The inhomogeneity of the intra-organ saponin distribution is highlighted, paving the way for future elegant structure/activity relationship investigations.

Identification of phenanthrene derivatives in Aerides rosea (Orchidaceae) using the combined systems HPLC-ESI-HRMS/MS and HPLC-DAD-MS-SPE-UV-NMR

INTRODUCTION

In our continued efforts to contribute to the general knowledge on the chemical diversity of orchids, we have decided to focus our investigations on the Aeridinae subtribe. Following our previous phytochemical study of Vanda coerulea, which has led to the identification of phenanthrene derivatives, a closely related species, Aerides rosea Lodd. ex Lindl. & Paxton, was chosen for investigation.

OBJECTIVE

To identify new secondary metabolites, and to avoid isolation of those already known, by means of the combined systems HPLC-DAD(diode-array detector) with high-resolution tandem mass spectrometry (HRMS/MS) and HPLC-DAD-MS-SPE(solid-phase extraction)-UV-NMR.

METHODS

A dereplication strategy was developed using a HPLC-DAD-HRMS/MS targeted method and applied to fractions from A. rosea stem extract. Characterisation of unknown minor compounds was then performed using the combined HPLC-DAD-MS-SPE-UV-NMR system.

RESULTS

The dereplication method allowed the characterisation of four compounds (gigantol, imbricatin, methoxycoelonin and coelonin), previously isolated from Vanda coerulea stem extract. The analyses of two fractions permitted the identification of five additional minor constituents including one phenanthropyran, two phenanthrene and two dihydrophenanthrene derivatives. The full set of NMR data of each compound was obtained from microgram quantities.

CONCLUSION

Nine secondary metabolites were characterised in A. rosea stems, utilising HPLC systems combined with high-resolution analytical systems. Two of them are newly described phenanthrene derivatives: aerosanthrene (5-methoxyphenanthrene-2,3,7-triol) and aerosin (3-methoxy-9,10-dihydro-2,5,7-phenanthrenetriol).

Introduction to hyphenated techniques and their applications in pharmacy

The hyphenated technique is developed from the coupling of a separation technique and an on-line spectroscopic detection technology. The remarkable improvements in hyphenated analytical methods over the last two decades have significantly broadened their applications in the analysis of biomaterials, especially natural products. In this article, recent advances in the applications of various hyphenated techniques, e.g., GC-MS, LC-MS, LC-FTIR, LC-NMR, CE-MS, etc. in the context of pre-isolation analyses of crude extracts or fraction from various natural sources, isolation and on-line detection of natural products, chemotaxonomic studies, chemical fingerprinting, quality control of herbal products, dereplication of natural products, and metabolomic studies are discussed with appropriate examples.

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.

Hyphenated techniques and their applications in natural products analysis

A technique where a separation technique is coupled with an online spectroscopic detection technology is known as hyphenated technique, e.g., GC-MS, LC-PDA, LC-MS, LC-FTIR, LC-NMR, LC-NMR-MS, and CE-MS. Recent advances in hyphenated analytical techniques have remarkably widened their applications to the analysis of complex biomaterials, especially natural products. This chapter focuses on the applications of hyphenated techniques to pre-isolation and isolation of natural products, dereplication, online partial identification of compounds, chemotaxonomic studies, chemical finger-printing, quality control of herbal products, and metabolomic studies, and presents specific examples. However, a particular emphasis has been given on the hyphenated techniques that involve an LC as the separation tool.

Simultaneous structural identification of natural products in fractions of crude extract of the rare endangered plant Anoectochilus roxburghii using H NMR/RRLC-MS parallel dynamic spectroscopy

Nuclear magnetic resonance/liquid chromatography-mass spectroscopy parallel dynamic spectroscopy (NMR/LC-MS PDS) is a method aimed at the simultaneous structural identification of natural products in complex mixtures. In this study, the method is illustrated with respect to ¹H NMR and rapid resolution liquid chromatography-mass spectroscopy (RRLC-MS) data, acquired from the crude extract of Anoectochilus roxburghii, which was separated into a series of fractions with the concentration of constituent dynamic variation using reversed-phase preparative chromatography. Through fraction ranges and intensity changing profiles in ¹H NMR/RRLC–MS PDS spectrum, ¹H NMR and the extracted ion chromatogram (XIC) signals deriving from the same individual constituent, were correlated due to the signal amplitude co-variation resulting from the concentration variation of constituents in a series of incompletely separated fractions. 1H NMR/RRLC-MS PDS was then successfully used to identify three types of natural products, including eight flavonoids, four organic acids and p-hydroxybenzaldehyde, five of which have not previously been reported in Anoectochilus roxburghii. In addition, two groups of co-eluted compounds were successfully identified. The results prove that this approach should be of benefit in the unequivocal structural determination of a variety of classes of compounds from extremely complex mixtures, such as herbs and biological samples, which will lead to improved efficiency in the identification of new potential lead compounds.

Discovery of new natural products by intact-cell mass spectrometry and LC-SPE-NMR: malbranpyrroles, novel polyketides from thermophilic fungus Malbranchea sulfurea

Six photosensitive polyketides, malbranpyrroles A-F, were discovered from the thermophilic fungus Malbranchea sulfurea by using intact-cell desorption/ionization on silicon mass (ICD-MS) and LC-SPE-NMR. These two strategies facilitate the searching and structural determination of unstable natural products. The ICD-MS indicated that only brown hyphae of M. sulfurea can produce malbranpyrroles. The biosynthetic pathway of malbranpyrroles was evidenced by 13C isotope precursors and amino acid feeding experiments. The cytotoxicity data revealed that the conformation of the conjugated system in malbranpyrroles does not affect cytotoxic potency against cancer cell lines. In addition, the chlorine atom was shown to be the pharmacophore for cytotoxicity.

New Polar Steroids from Starfish

A short review concerning new polar steroids isolated from starfish with 75 citations is given. This review covers the literature published from 2001 through 2007. The emphasis is on new structures, together with their relevant biological activities, source organisms, and localities of collections.

Phytochemical analysis of the Southern Australian marine alga, Plocamium mertensii using HPLC-NMR

INTRODUCTION

Over the last decade HPLC-NMR has become a robust analytical technique that has been applied to a wide range of studies, particularly plant extracts. There have been only a few applications of the use of HPLC-NMR to profile marine natural product extracts and no studies involving marine algae. The marine alga selected for this study belongs to the genus Plocamium, which is a well known source of polyhalogenated monoterpenes.

OBJECTIVE

To chemically profile the marine alga P. mertensii, using a combination of on-line (HPLC-NMR) and off-line approaches.

METHODOLOGY

P. mertensii was extracted with 3:1 methanol-dichloromethane and subsequently partitioned into dichloromethane and methanol-soluble fractions. The methanol partition was exclusively profiled by HPLC-NMR (on-flow, stop-flow and time-slice experiments) whilst the dichloromethane partition was investigated by conventional isolation and purification procedures.

RESULTS

HPLC-NMR analysis of the methanol partition partially identified the presence of the major compounds 7, 13, 27 and 37, the structures of which were unequivocally elucidated by off-line characterisation of the dichloromethane partition. Two additional minor metabolites (3 and 8) present in the dichloromethane partition were only tentatively identified as these co-occurred in a mixture with compounds 7 and 13. As a result of this study a number of chemical shift reassignments were made for compound 37.

CONCLUSION

This is one of the few reports describing the application of HPLC-NMR to rapidly profile or dereplicate a marine organism and the first application of HPLC-NMR to successfully profile the chemistry of a marine alga.

Multiple ionization mass spectrometry strategy used to reveal the complexity of metabolomics

A multiple ionization mass spectrometry strategy is presented based on the analysis of human serum extracts. Chromatographic separation was interfaced inline with the atmospheric pressure ionization techniques electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in both positive (+) and negative (-) ionization modes. Furthermore, surface-based matrix-assisted laser desorption/ionization (MALDI) and desorption ionization on silicon (DIOS) mass spectrometry were also integrated with the separation through fraction collection and offline mass spectrometry. Processing of raw data using the XCMS software resulted in time-aligned ion features, which are defined as a unique m/z at a unique retention time. The ion feature lists obtained through LC-MS with ESI and APCI interfaces in both +/- ionization modes were compared, and unique ion tables were generated. Nonredundant, unique ion features, were defined as mass numbers for which no mass numbers corresponding to [M + H](+), [M - H](-), or [M + Na](+) were observed in the other ionization methods at the same retention time. Analysis of the extracted serum using ESI for both (+) and (-) ions resulted in >90% additional unique ions being detected in the (-) ESI mode. Complementing the ESI analysis with APCI resulted in an additional approximately 20% increase in unique ions. Finally, ESI/APCI ionization was combined with fraction collection and offline-MALDI and DIOS mass spectrometry. The parts of the total ion current chromatograms in the LC-MS acquired data corresponding to collected fractions were summed, and m/z lists were compiled and compared to the m/z lists obtained from the DIOS/MALDI spectra. It was observed that, for each fraction, DIOS accounted for approximately 50% of the unique ions detected. These results suggest that true global metabolomics will require multiple ionization technologies to address the inherent metabolite diversity and therefore the complexity in and of metabolomics studies.

Rapid structural determination of new trace cassaine-type diterpenoid amides in fractions from Erythrophleum fordii by liquid chromatography-diode-array detection/electrospray ionization tandem mass spectrometry and liquid chromatography/nuclear magnetic resonance

Electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn), and combination with HPLC (HPLC/ESI-MSn), have been extensively applied to on-line analysis of natural products. Hyphenation of liquid chromatography to nuclear magnetic resonance spectroscopy (HPLC/NMR) has been developed in the last decade, which is utilized for the analysis of metabolites and drug impurities. In the study reported here, the fragmentation behaviors of eight cassaine-type diterpenoid amides from Erythrophleum fordii were investigated by ESI-MSn. The fragmentation rules and NMR spectral characteristics are summarized, and the relationship among the rules, characteristics and the structures is described. According to the fragmentation rules and NMR spectral characteristics, seven trace constituents and two formerly obtained compounds of cassaine-type diterpenoid amides in the fractions from E. fordii were structurally characterized on the basis of HPLC/HRMS, HPLC-DAD/ESI-MSn, HPLC/1H NMR and HPLC/1H-1H COSY rapidly. Among them, constituents 1-5 are new compounds, and 6 and 7 are reported from E. fordii for the first time. The aim is to develop an effective analytical method for structural identification of new trace natural products in plants.

Application of high-performance liquid chromatography–nuclear magnetic resonance coupling to the identification of limonoids from mahogany tree (Switenia macrophylla, Meliaceae) by stopped-flow 1D and 2D NMR spectroscopy

Separation and characterization of limonoids from Switenia macrophylla (Meliaceae) by HPLC-NMR technique has been described. Analyses were carried out using reversed-phase gradient HPLC elution coupled to NMR (600 MHz) spectrometer in stopped-flow mode. Separated peaks were collected into an interface unit prior to NMR measurements, which were performed with suppression of solvent signals by shaped pulses sequences. Structure elucidation of the limonoids was attained by data obtained from 1H NMR, TOCSY, gHSQC and gHMBC spectra without conventional isolation that is usually applied in natural products studies.

Development of HPLC/ESI-MS and HPLC/1H NMR Methods for the Identification of Photocatalytic Degradation Products of Iodosulfuron

In the present study, HPLC/ESI-MS and stopped-flow HPLC/1H NMR methods were developed and applied to separate and characterize the byproducts arising from TiO2-catalyzed photodegradation of the herbicide iodosulfuron methyl ester (IOME) in aqueous solution under UV irradiation. Prior to identification, irradiated solutions of IOME (200 and 1000 mg.L(-1)) were concentrated by solid-phase extraction using two cartridges: Isolute C18 and Isolute ENV+. Analytical separation was achieved on a C18 reversed-phase column with ACN/H2O (HPLC/MS) or ACN/D2O (HPLC/NMR) as mobile phase and a linear gradient with a chromatographic run time of 35 min. The combination of UV and MS data allowed the structural elucidation of more than 20 degradation products, whereas 1H NMR data permitted an unequivocal confirmation of the identities of major products and the differentiation of several positional isomers, in particular, the hydroxylation isomers. The obtained results permitted us to propose a possible degradation scheme and to put in evidence the presence of privileged sites for the attack of OH radicals. This work shows, for the first time, the application of combined HPLC with UV, MS, and NMR detection for complete structural elucidation of photocatalytic degradation products, and it will be of particular value in studies on the elimination of pollutants in aqueous solutions by photocatalysis.

The application of LC–NMR and LC–MS for the separation and rapid structure elucidation of an unknown impurity in 5-aminosalicylic acid

This work has demonstrated the usefulness of combining liquid chromatography-nuclear magnetic resonance spectroscopy (LC-NMR) and liquid chromatography-mass spectrometry (LC-MS) methodologies for a rapid identification of an unknown impurity (N1) in the drug 5-aminosalycilic acid. Complementary information obtained from the two methods has revealed plenty of structural information and led to the fast on-line structure determination of N1 prior to its isolation and purification. The analysis of LC-NMR and LC-MS spectra revealed that N1 and 5-aminosalycilic acid are structurally closely related compounds. The structure of N1 was later confirmed by high-resolution NMR spectroscopy of the isolated compound and the atom assignment was made. The approach described here has potential for 5-aminosalycilic acid impurity profiling and monitoring the production process.

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.

Identification of secondary metabolites from Streptomyces violaceoruber TU22 by means of on-flow LC-NMR and LC-DAD-MS

For rapid screening of natural products from Actinomycetes, a combination of on-line couplings LC-NMR, LC-DAD-MS and HPLC-PDA, as well as MALDI-TOF-MS is particularly suitable. Simultaneous use of these coupling techniques provides considerable advantages for the rapid identification of natural compounds in mixtures. The results of our present investigation on secondary metabolite products of Streptomyces violaceoruber TU 22 showed that more than 50% of the identified metabolites are new compounds. The structures of four new polyketides (granaticin C, metenaticin A, B and C) as well as four known ones (granaticin A, granatomycin E, daidzein and genistein) have been elucidated using LC-NMR, LC-MS/MS and -MS(n) techniques in combination with two-dimensional NMR spectroscopy.

LC-NMR coupling technology: recent advancements and applications in natural products analysis

An overview of recent advances in nuclear magnetic resonance (NMR) coupled with separation technologies and their application in natural product analysis is given and discussed. The different modes of LC-NMR operation are described, as well as how technical improvements assist in establishing LC-NMR as an important tool in the analysis of plant-derived compounds. On-flow, stopped-flow and loop-storage procedures are mentioned, together with the new LC-SPE-NMR configuration. The implementation of mass spectrometry in LC-NMR is also useful on account of the molecular weight and fragmentation information that it provides, especially when new plant species are studied. Cryogenic technology and capillary LC-NMR are the other important recent developments. Since the plant kingdom is endless in producing potential drug candidates, development and optimization of LC-NMR techniques convert the study of natural products to a less-time-consuming task, speeding up identification.

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

Miniaturization and hyphenation of chromatographic separation techniques to nuclear magnetic resonance spectroscopy is being increasingly demanded in the field of biomedical, drug metabolite and natural product analysis. Herein, capillary liquid chromatography was coupled on-line to microcoil 1H nuclear magnetic resonance spectroscopy (capLC-NMR) equipped with a 1.5 microL solenoidal probe for structure elucidation of isoflavones in Radix astragali. The extract was screened by HPLC-UV-MS as the preliminary step and four major peaks were identified tentatively by ion trap mass spectrometry molecular weights and characteristic fragments. Then, stopped-flow capLC-UV-NMR was performed using 33 microg extract injected on-column. The four peaks were parked manually in the micro probe one by one and corresponding 1H NMR spectra were recorded with good resolutions under the applied capLC-NMR conditions (120 and 220 ng injected on-column for peaks 2 and 4, respectively). All aromatic regions of 1H NMR spectra correlated well to the characteristic signals of isoflavone aglycone protons. And the signal corresponding to the anomeric proton of the glucopyranoside of isoflavone glycoside was also obtained for peak 1. Therefore, these four peaks are determined as calycosin-7-O-beta-D-glucopyranoside (1), ononin (2), calycosin (3) and formononetin (4) unambiguously. The capLC-NMR results indicate that this hyphenated technique could be used for the determination of a great variety of natural products from small sample amounts, e.g., only 5 g R. astragali in this study.

Optimization of a matrix solid-phase dispersion method with subsequent clean-up for the determination of ethylene bisdithiocarbamate residues in almond samples

A matrix solid-phase dispersion (MSPD) method with subsequent clean-up has been developed to isolate the ethylene bisdithiocarbamate (EBDC) main metabolites (ethylenethiourea, ETU, and ethylenebis [isothiocyanate] sulphide, EBIS) in almond samples. The optimized experimental set-up configuration involved 0.2 g of almond sample, washed sand as MSPD support and NaOH as defatting agent. A subsequent purification step on alumina using acetonitrile as extraction solvent was enough to remove all interferent matrix components, including the fatty material, and provide clean extracts. Quantitative analysis was performed by reversed phase liquid chromatography (RPLC) with diode-array ultraviolet absorbance (DAD UV) detector. Analytes recoveries were between 76 and 85% with relative standard deviations ranging from 3 to 12%. The low limits of quantification of 0.05 and 0.07 mg kg(-1) achieved for ETU and EBIS, respectively, make the method useful for the determination of EBDC residues on almond samples.

LC-UV-solid-phase extraction-NMR-MS combined with a cryogenic flow probe and its application to the identification of compounds present in Greek oregano

Structure elucidation of natural products usually relies on a combination of NMR spectroscopy with mass spectrometry whereby NMR trails MS in terms of the minimum sample amount required. In the present study, the usefulness of on-line solid-phase extraction (SPE) in LC-NMR for peak storage after the LC separation prior to NMR analysis is demonstrated. The SPE unit allows the use of normal protonated solvents for the LC separation and fully deuterated solvents for flushing the trapped compounds to the NMR probe. Thus, solvent suppression is no longer necessary. Multiple trapping of the same analyte from repeated LC injections was utilized to solve the problem of low concentration and to obtain 2D heteronuclear NMR spectra. In addition, a combination of the SPE unit with a recently developed cryoflow NMR probe and an MS was evaluated. This on-line LC-UV-SPE-NMR-MS system was used for the automated analysis of a Greek oregano extract. Combining the data provided by the UV, MS, and NMR spectra, the flavonoids taxifolin, aromadendrin, eriodictyol, naringenin, and apigenin, the phenolic acid rosmarinic acid, and the monoterpene carvacrol were identified. This automated technique is very useful for natural product analysis, and the large sensitivity improvement leads to significantly reduced NMR acquisition times.

Determination and identification of isoflavonoids in Radix astragali by matrix solid-phase dispersion extraction and high-performance liquid chromatography with photodiode array and mass spectrometric detection

The isoflavonoids in Radix astragali were determined and identified by HPLC-photodiode array detection-MS after extraction employing matrix solid-phase dispersion (MSPD). As a new sample preparation method for R. astragali, the MSPD procedure was optimized, validated and compared with conventional methods including ultrasonic and Soxhlet extraction. The amounts of two major components in this herb, formononetin (6) and ononin (2), were determined based on their authentic standards. Four major isoflavonoids, formononetin (6), ononin (2), calycosin (5) and its glycoside (1), and three minor isoflavonoids, (6aR,11aR)-3-hydroxy-9, 10-dimethoxypterocarpan (7), its glycoside (3), and (3R)-7,2'-dihydroxy-3',4'-dimethoxyisoflavone-7-O-beta-D-glycoside (4), were identified based on their characteristic two-band UV spectra and [M + H], [aglycone + H]+ and [A1 + H]+ ions, etc. The combined MSPD and HPLC-DAD-MS method was suitable for quantitative and qualitative determination of the isoflavonoids in R. astragali.

Method development in high-performance liquid chromatography for high-throughput profiling and metabonomic studies of biofluid samples

"Metabonomics" has in the past decade demonstrated enormous potential in furthering the understanding of, for example, disease processes, toxicological mechanisms, and biomarker discovery. The same principles can also provide a systematic and comprehensive approach to the study of food ingredient impact on consumer health. However, "metabonomic" methodology requires the development of rapid, advanced analytical tools to comprehensively profile biofluid metabolites within consumers. Until now, NMR spectroscopy has been used for this purpose almost exclusively. Chromatographic techniques and in particular HPLC, have not been exploited accordingly. The main drawbacks of chromatography are the long analysis time, instabilities in the sample fingerprint and the rigorous sample preparation required. This contribution addresses these problems in the quest to develop generic methods for high-throughput profiling using HPLC. After a careful optimization process, stable fingerprints of biofluid samples can be obtained using standard HPLC equipment. A method using a short monolithic column and a rapid gradient with a high flow-rate has been developed that allowed rapid and detailed profiling of larger numbers of urine samples. The method can be easily translated into a slow, shallow-gradient high-resolution method for identification of interesting peaks by LC-MS/NMR. A similar approach has been applied for cell culture media samples. Due to the much higher protein content of such samples non-porous polymer-based small particle columns yielded the best results. The study clearly shows that HPLC can be used in metabonomic fingerprinting studies.

Hyphenation and hypernation the practice and prospects of multiple hyphenation

In the past two decades, combining a chromatographic separation system on-line with a spectroscopic detector in order to obtain structural information on the analytes present in a sample has become the most important approach for the identification and/or confirmation of the identity of target and unknown chemical compounds. In most instances, such hyphenation can be accomplished by using commercially available equipment For most (trace-level) analytical problems encountered today, the combination of column liquid chromatography or capillary gas chromatography with a mass spectrometer (LC-MS and GC-MS, respectively) is the preferred approach. However, it is also true that additional and/or complementary information is, in quite a number of cases, urgently required. This can be provided by, for example, atomic emission, Fourier-transform infrared, diode-array UV-vis absorbance or fluorescence emission, or nuclear magnetic resonance spectrometry. In the present review, the various options are briefly discussed and a few relevant applications are quoted for each combination. Special attention is devoted to systems in which multiple hyphenation, or hypernation, is an integral part of the setup. As regards this topic, the relative merits of various combinations--which turn out to include a mass spectrometer as one of the detectors in essentially all cases--are discussed and the fundamental differences between GC- and LC-based systems are outlined. Finally, the practicability of more extensive hypernation in LC, viz. with up to four spectrometers, is discussed. It is demonstrated that, technically, such multiple hyphenation is possible and that, from a practical point of view, rewarding results can be obtained. In other words, further research in this area is certainly indicated. However, in the foreseeable future, using several separate conventional hyphenated systems will be the commonly implemented solution in most instances.

Liquid chromatography with ultraviolet absorbance-mass spectrometric detection and with nuclear magnetic resonance spectroscopy: a powerful combination for the on-line structural investigation of plant metabolites

In order to discover new bioactive compounds from plant sources which could become new leads or new drugs, extracts should be submitted at the same time to chemical screening and to various biological or pharmacological targets. Metabolite profiling using hyphenated techniques such as LC/UV, LC/MS and more recently LC/NMR, quickly provides plenty of structural information, leading to a partial or a complete on-line de novo structure determination of the natural products of interest. As a complement to this approach, bioassays performed after LC/microfractionation of the extracts allow efficient localisation of the bioactive LC-peaks in the chromatograms. The combination of metabolite profiling and LC/bioassays provides the possibility of distinguishing between already known bioactive compounds (dereplication) and new molecules directly in crude plant extracts. Thus, the tedious isolation of compounds of low interest can be avoided and targeted isolation of new bioactive products or constituents presenting novel or unusual spectroscopic features can be undertaken. Several examples of rapid localisation of bioactive compounds, based on post-chromatographic bioautographic testing of LC/NMR microfractions and subsequent on-line identification will be illustrated. Application of hyphenated techniques for the efficient characterisation of labile constituents or constituents difficult to separate at the preparative scale will also be mentioned. The possibilities and limitations of LC/UV/NMR/MS and LC/bioassay as well as future development expected in this field will be discussed.

Liquid chromatography-(tandem) mass spectrometry of selected emerging pollutants (steroid sex hormones, drugs and alkylphenolic surfactants) in the aquatic environment

Among the various compounds considered as emerging pollutants, alkylphenolic surfactants, steroid sex hormones, and pharmaceuticals are of particular concern, both because of the volume of these substances used and because of their activity as endocrine disruptors or as causative agents of bacterial resistance, as is the case of antibiotics. Today, the technique of choice for analysis of these groups of substances is liquid-chromatography coupled to mass spectrometry (LC-MS) and tandem mass spectrometry (LC-MS-MS). In the last decades, this technique has experienced an impressive progress that has made possible the analysis of many environmental pollutants in a faster, more convenient, and more sensitive way, and, in some cases, the analysis of compounds that could not be determined before. This article reviews the LC-MS and LC-MS-MS methods published so far for the determination of alkylphenolic surfactants, steroid sex hormones and drugs in the aquatic environment. Practical considerations with regards to the analysis of these groups of substances by using different mass spectrometers (single quadrupole, ion trap and triple quadrupole instruments, etc.), interfaces and ionization and monitoring modes, are presented. Sample preparation aspects, with special focus on the application of advanced techniques, such as immunosorbents, restricted access materials and molecular imprinted materials, for extraction/purification of aquatic environmental samples and extracts are also discussed.

Progress in liquid chromatography-mass spectrometry instrumentation and its impact on high-throughput screening

In the past 10 years, liquid chromatography-mass spectrometry (LC-MS) has rapidly matured to become a very powerful and useful analytical tool that is widely applied in many areas of chemistry, pharmaceutical sciences and biochemistry. In this paper, recent instrumental developments in LC-MS-related interfacing, ionization and mass analysis are reviewed from the perspective of the application of LC-MS in high-throughput screening of combinatorial libraries and the related high-throughput quantitative bioanalysis in early drug-discovery studies, such as early adsorption, distribution, metabolism and excretion studies.

Flow NMR applications in combinatorial chemistry

Flow NMR techniques are now well accepted and widely used in many areas of drug discovery. Although natural-product-, rational-drug-design-, and NMR-screening-programs have begun to use flow NMR more routinely, flow NMR has not yet gained widespread acceptance in combinatorial chemistry, even though it has been shown to be a potentially useful tool. Recent developments in DI-NMR, FIA-NMR, and LC-NMR will help flow NMR eventually gain a wider acceptance within combinatorial chemistry. These developments include LC-NMR-MS instrumentation, flow probe improvements, new pulse sequences, improved automation of NMR data analysis, and the application of flow NMR to related fields in drug discovery.

HPLC-NMR/HPLC-MS analysis of the bark extract of Stauranthus perforatus

A combination of HPLC-MS and HPLC-NMR techniques has been used to analyse the cytotoxic fractions of the dichloromethane extract of bark of Stauranthus perforatus. Six furanocoumarins (byakangelicol, heraclenin, heraclenol, imperatorin, isopimpinellin and xanthotoxin) and nine quinoline alkaloids (two known compounds, veprisine and 5-hydroxy-1-methyl-2-phenyl-4-quinolone, along with seven novel compounds, stauranthine, 3',4'-dihydroxy-3',4'-dihydroveprisine, 3',4'-dihydroxy-3',4'-dihydrostauranthine, 3',6'-dihydroxy-3',6'-dihydroveprisine, 3',6'-dihydroxy-3',6'-dihydrostauranthine, 6'-hydroxy-3'-ketoveprisine and 6'-hydroxy-3'-ketostauranthine) have been identified in the fractions.

On-line liquid-chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry coupling for the separation and characterization of secoisolariciresinol diglucoside isomers in flaxseed

Two secoisolariciresinol diglucoside (SDG) diastereomers were extracted from flaxseed and liberated through alkaline hydrolysis. Anion-exchange and reversed-phase chromatography were successfully employed to purify the hydrolyzed flaxseed extract. On-line LC-NMR-MS analyses revealed the structure of the isolated and purified SDG diastereomers, [2R,2'R]-2,3-bis[(4-hydroxy-3-methoxyphenyl)-methyl]-1,4-butanediyl-bis-beta-glucopyranoside the predominant flaxseed lignan and [2R,2'S]-2,3-bis[(4-hydroxy-3-methoxyphenyl)methyl]-1,4-butanediyl-bis-beta-glucopyranoside, a previously incompletely characterized minor flaxseed lignan. Circular dichroism (CD) analyses confirmed the presence of two distinguished optically active compounds present in the flaxseed extract.

Use of on-line liquid chromatography-nuclear magnetic resonance spectroscopy for the rapid investigation of flavonoids from Sorocea bomplandii

This paper reports the identification of di- and triglycosylated flavonoids from Sorocea bomplandii (Moraceae) by liquid chromatography coupled on-line to nuclear magnetic resonance (LC-NMR). These glycosylated flavonoids may be used as a taxonomic marker in future work.