Combination of LC-MS and LC-NMR as a Tool for the Structure Determination of Natural 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.

Minor Nortriterpenoids from the Twigs and Leaves of Rhododendron latoucheae

A hyphenated NMR technique (analytical HPLC with a DAD connected to MS, SPE, and NMR) has proven effective for the full structural analysis and identification of minor natural products in complex mixtures. Application of this hyphenated technique to the CH₂Cl₂-soluble fraction of Rhododendron latoucheae led to the identification of 15 new minor ursane-type 28-nortriterpenoids (1-15). Compounds 1 and 12 inhibited HSV-1 with IC₅₀ values of 6.4 and 0.4 μM, respectively.

Natural Products Diversity of Marine Ascidians (Tunicates; Ascidiacea) and Successful Drugs in Clinical Development

This present study reviewed the chemical diversity of marine ascidians and their pharmacological applications, challenges and recent developments in marine drug discovery reported during 1994-2014, highlighting the structural activity of compounds produced by these specimens. Till date only 5% of living ascidian species were studied from <3000 species, this study represented from family didemnidae (32%), polyclinidae (22%), styelidae and polycitoridae (11-12%) exhibiting the highest number of promising MNPs. Close to 580 compound structures are here discussed in terms of their occurrence, structural type and reported biological activity. Anti-cancer drugs are the main area of interest in the screening of MNPs from ascidians (64%), followed by anti-malarial (6%) and remaining others. FDA approved ascidian compounds mechanism of action along with other compounds status of clinical trials (phase 1 to phase 3) are discussed here in. This review highlights recent developments in the area of natural products chemistry and biotechnological approaches are emphasized.

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).

Chemical dereplication of wine stilbenoids using high performance liquid chromatography-nuclear magnetic resonance spectroscopy

Wine is a major dietary source of numerous potentially health promoting stilbenoids that have been the subject of many qualitative and quantitative studies. However, our initial HPLC-MS analyses of crude wine samples demonstrated the presence of compounds with molecular weights matching characteristic stilbenoid dimers, trimers, and tetramers that were unaccounted for in the literature. Due to the likelihood that these are known compounds, a chemical dereplication method is highly desirable. We developed such a method using LC-DAD-MS monitored fractionation steps, using adsorption and centrifugal partition chromatography (CPC), to obtain fractions rich in stilbenoids for analysis in stopped-flow LC-NMR. (1)H NMR spectra and MS data were cross-referenced with our laboratory database and the literature for identification. This method yielded highly useful structural information, allowing the characterization of previously unidentified stilbenoids in wine, ampelopsin C, isohopeaphenol, quadrangularin A, and E-ω-viniferin. These results demonstrate the usefulness of stop-flow LC-NMR in conjunction with LC-MS guided fractionation for the dereplication of compounds of interest in general, and specifically for expanding the current knowledge of wine chemistry.

Rationale for a natural products approach to herbicide discovery

Weeds continue to evolve resistance to all the known modes of herbicidal action, but no herbicide with a new target site has been commercialized in nearly 20 years. The so-called 'new chemistries' are simply molecules belonging to new chemical classes that have the same mechanisms of action as older herbicides (e.g. the protoporphyrinogen-oxidase-inhibiting pyrimidinedione saflufenacil or the very-long-chain fatty acid elongase targeting sulfonylisoxazoline herbicide pyroxasulfone). Therefore, the number of tools to manage weeds, and in particular those that can control herbicide-resistant weeds, is diminishing rapidly. There is an imminent need for truly innovative classes of herbicides that explore chemical spaces and interact with target sites not previously exploited by older active ingredients. This review proposes a rationale for a natural-products-centered approach to herbicide discovery that capitalizes on the structural diversity and ingenuity afforded by these biologically active compounds. The natural process of extended-throughput screening (high number of compounds tested on many potential target sites over long periods of times) that has shaped the evolution of natural products tends to generate molecules tailored to interact with specific target sites. As this review shows, there is generally little overlap between the mode of action of natural and synthetic phytotoxins, and more emphasis should be placed on applying methods that have proved beneficial to the pharmaceutical industry to solve problems in the agrochemical industry.

Steroidal glycosides from Dregea sinensis var. corrugata screened by liquid chromatography-electrospray ionization tandem mass spectrometry

The MS fragmentation behavior of the C-21 steroidal glycosides from Dregea sinensis var. corrugata was investigated by positive and negative ion electrospray ionization MS using a multistage tandem mass spectrometer equipped with an ion trap analyzer. The mass fragmentation patterns of steroidal glycosides substituted with an orthoacetate group were summarized, and the fragmentation patterns were applied to the online structure identification of the steroidal glycosides in the extract. Eighteen new C-21 steroidal glycosides were identified by means of HPLC-HRESIMS and HPLC-DAD-ESIMS(n). Three new compounds (1, 4, and 7) were identified by HPLC-DAD-ESIMS(n), and their structures were elucidated by use of 1D and 2D NMR methods. The structures identified by MS are fully consistent with those elucidated by NMR data. The present study shows that HPLC-DAD-ESIMS(n) can be used as an effective tool to rapidly identify compounds and guide the isolation of target compounds from crude plant extracts.

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.

Quantitative 1H NMR: development and potential of a method for natural products analysis

Based on a brief revision of what constitutes state-of-the-art "quantitative experimental conditions" for (1)H quantitative NMR (qHNMR), this comprehensive review contains almost 200 references and covers the literature since 1982 with emphasis on natural products. It provides an overview of the background and applications of qHNMR in natural products research, new methods such as decoupling and hyphenation, and analytical potential and limitations, and compiles information on reference materials used for and studied by qHNMR. The dual status of natural products, being single chemical entities and valuable biologically active agents that need to be purified from complex matrixes, results in an increased analytical demand when testing their deviation from the singleton composition ideal. The outcome and versatility of reported applications lead to the conclusion that qHNMR is currently the principal analytical method to meet this demand. Considering both 1D and 2D (1)H NMR experiments, qHNMR has proved to be highly suitable for the simultaneous selective recognition and quantitative determination of metabolites in complex biological matrixes. This is manifested by the prior publication of over 80 reports on applications involving the quantitation of single natural products in plant extracts, dietary materials, and materials representing different metabolic stages of (micro)organisms. In summary, qHNMR has great potential as an analytical tool in both the discovery of new bioactive natural products and the field of metabolome analysis.

Determination of pigments in vegetables

Plant pigments are responsible for the shining color of plant tissues. They are also found in animal tissues and, eventually in transformed food products as additives. These pigments have an important impact on the commercial value of products, because the colors establish the first contact with the consumer. In addition plant pigments may have an influence on the health of the consumers. Pigments are labile: they can be easily altered, and even destroyed. Analytical processes have been developed to determine pigment composition. The aim of this paper is to provide a brief overview of these methods.

Full absolute stereostructures of natural products directly from crude extracts: The HPLC-MS/ MS-NMR-CD 'triad'

This chapter deals with an efficient methodology available in our Center of Excellence, BIOTECmarin: the novel analytical 'triad' HPLC-MS/MS-NMR-CD. By this method, which was, in this complemented form, first introduced into phytochemical research by our group, we can not only rapidly identify known structures, but can also investigate new metabolites and establish their full absolute stereostructures online, directly from crude extracts, without the necessity of first isolating the compounds. The LC-CD option, which we have been using for the first time in natural products analysis, becomes even more valuable by the possibility of interpreting the online CD spectra by their simulation or prediction through quantum chemical calculation, thus avoiding the usual, often risky, empirical comparison with the CD spectra of (sometimes not so related) compounds of known absolute stereostructure or the application of (sometimes not really applicable) likewise empirical CD rules. The hyphenated analytical methods are additionally complemented by our synthetic expertise, again involving new concepts and strategies developed in our group. The methods and their application will first be explained and exemplified for plant-derived ('terrestrial') natural products, for which they were initially developed, and will then be applied to the online structural elucidation of novel natural products from marine organisms.

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.

LC-NMR applied to the characterisation of cardiac glycosides from three micropropagated Isoplexis species

Species of the genus Isoplexis are of particular interest with respect to the biochemical pathway leading to the cardenolides. It is important to determine whether or not 5beta-configured compounds, typically produced by Digitalis species and used in medicine, are present together with their respective alpha-isomers in Isoplexis spp. Structure elucidation by LC-NMR of the products isolated from in vitro regenerated Isoplexis canariensis, I. chalcantha and I. isabelliana was carried out, and similarities were observed among the products of the three species, including the presence of digitoxigenin-type cardenolides in I. canariensis and xysmalogenin and canarigenin derivatives in I. chalcantha never previously reported in these species. Pregnane glycosides not found until now either in Isoplexis or Digitalis were also detected.

Review of the analytical techniques for sesquiterpenes and sesquiterpene lactones

In this paper the analytical techniques of about the last 2 decades for sesquiterpenes including their lactones are reviewed. For sesquiterpenes, methods like GC, GC-EI-MS, GC-CI-MS, GC-MS-MS, GC-FT-IR, GC-UV, GC-AES, 13C-NMR, PY-GC-MS, HPLC, HPLC-TSP, SFE, SFC, SFC-UV are available, GC combined with MS is the most widespread. Sesquiterpene lactones can be analysed by HPLC, HPLC-TSP, HPLC-APCI, HPLC-ESI, HPLC-PB, HPLC-NMR, SFC, MEKC, GC, GC-MS, TLC and OPLC. Here HPLC is the method of choice. The usefulness of the individual methods are briefly discussed.

Structural characterization of the oxidative degradation products of an antifungal agent SCH 56592 by LC–NMR and LC–MS

LC-NMR and LC-MS were used to characterize the structures of four major degradation products of SCH 56592, an antifungal drug candidate in clinical trials. These compounds were formed under stress conditions in which the bulk drug substance was heated in air at 150 degrees C for 12 days, and were separated from SCH 56592 as a mixture using a semi-preparative HPLC method. The data from LC-NMR, LC-ESI-MS (electrospray ionization mass spectrometry) and LC-ESI-MS/MS indicate that the oxidation occurred at the piperazine ring in the center of the drug molecule. The structures of the degradation products were determined from the 1H NMR spectra obtained via LC-NMR, which were supported by LC-ESI-MS and LC-ESI-MS/MS analyses. A novel degradation pathway of SCH 56592 was proposed based on these characterized structures.

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

A combination of matrix solid-phase dispersion extraction (MSPD) and LC-NMR-MS hyphenation is proposed as a rapid screening method of natural products for unknown compounds. In this report, this new analytical approach is applied for the first time. MSPD represents a significant simplification compared to classical extraction procedures and is thus an excellent complement to the fast and powerful LC-NMR-MS: MSPD yields extracts suitable for LC-NMR-MS in one simple preparation step, while LC-NMR-MS yields a wealth of information in one single chromatographic run. The suitability of this technique to characterise glycosidic compounds in the molecular mass range of 1200 to 1400 a.m.u. is demonstrated. The information on the number of exchangeable protons provided by an additional back-exchange experiment proved to be particularly valuable for structural elucidation. The possibility of semi-quantitative LC-NMR measurements through methyl signals H(3)-18 and 19 of the steroidal skeleton is demonstrated and is ensuingly used to provide relative quantitative data of the steroid oligosaccharide fraction.

NMR spectroscopy in drug discovery: tools for combinatorial chemistry, natural products, and metabolism research

NMR spectroscopy has enjoyed many advances recently, and the pace of development shows no signs of slowing. This article focuses on advances that have affected solution-state NMR. These advances fall into three general categories: new experimental techniques (new pulse sequence tools), improved hardware and more powerful software. These advances are allowing NMR to help solve important problems in the field of drug discovery. Their impact is widespread. NMR spectroscopy is now being used to determine protein structures, to monitor ligand-receptor binding, to study diffusion, to analyze mixtures using LC-NMR, to analyze solid-phase synthesis resins and to determine the structures of organic small molecules. NMR spectroscopy can provide both qualitative and quantitative information, and can be used in both routine analytical applications and demanding research applications. The applications described here can benefit numerous disciplines in drug discovery, including natural products research, synthetic medicinal chemistry, metabolism studies, drug production, quality control, rational drug design and combinatorial chemistry.

The potential of LC-NMR in phytochemical analysis

The coupling of high performance liquid chromatography with nuclear magnetic resonance spectroscopy (LC-NMR) is one of the most powerful methods for the separation and structural elucidation of unknown compounds in mixtures. The recent progress in pulse field gradients and solvent suppression, the improvement in probe technology, and the construction of high field magnets have given a new stimulus to this technique, which has emerged since the mid 1990s as a very efficient method for the on-line identification of organic molecules. LC-NMR thus represents a potentially interesting complementary technique to LC-UV-MS in phytochemical analysis for the detailed on-line structural analysis of natural products. Recent applications have fully demonstrated the usefulness of this technique. A brief review of the applications of LC-NMR in natural product chemistry is presented in this paper, and a summary of the basic principles and modes of operation of LC-NMR is provided. Selected examples of LC-NMR analyses of plant metabolites in crude extracts or in enriched fractions are outlined and used to illustrate the different strategies for employing the technique. The practical possibilities and limitations of LC-NMR in its application to the analysis of crude plant extracts are discussed by means of several examples. Analytical strategies involving LC multi-coupled (hyphenated) techniques for the chemical screening and dereplication of crude plant extracts are presented. An analysis of the future development of the technique with respect to its application in phytochemical analysis is also given.

Hydrogen peroxide and flavan-3-ols in storage roots of cassava (Manihot esculenta crantz) during postharvest deterioration

Cassava storage roots are an important staple food throughout the lowland humid tropics. However, cassava suffers from a poorly understood storage disorder, known as postharvest physiological deterioration (PPD), which constrains its exploitation. In an attempt to broaden the understanding of PPD, nine different cassava cultivars were analyzed for specific compounds accumulating during the process. The production of hydrogen peroxide (H(2)O(2)) is involved in the early stages of PPD in cassava roots. H(2)O(2) was quantified and localized histochemically at the tissue and cell level in deteriorating roots. This reactive oxygen species accumulated during the first 24 h after harvest, especially in the inner parenchymatic tissue. Three flavan-3-ols, (+)-catechin, (+)-catechin gallate, and (+)-gallocatechin, accumulated during the storage of cassava roots. However, these potential antioxidants cannot be related to early storage disorders or wound responses because they start to accumulate only after 4-6 days.

Directly coupled HPLC-NMR and HPLC-NMR-MS in pharmaceutical research and development

The methodology for the direct coupling of HPLC with NMR spectroscopy and the simultaneous double coupling of HPLC with NMR and mass spectrometry (MS) is described. Indications of the necessary technical developments to achieve this are given, and the applications of these new techniques to studies of pharmaceutical relevance are reviewed. These include studies of combinatorial chemistry libraries, synthetic chemical impurities, characterisation of drug mixtures, identification of natural products of possible pharmaceutical interest and identification of xenobiotic metabolites in human, animal and in vitro systems. In addition, HPLC-NMR has been used to investigate xenobiotic metabolite reactivity. Finally, the potential future directions of the techniques are discussed.

Application of liquid chromatography-nuclear magnetic resonance spectroscopy to the identification of natural products

LC-NMR combines the separation power of high-performance liquid chromatography (HPLC) with the superior structural information content of nuclear magnetic resonance (NMR). These two techniques traditionally have been the primary tools used by natural products chemists to isolate and determine the structures of molecules of interest. Recent advances in NMR technology have allowed the practical application of LC-NMR, thus providing natural products chemists with a hyphenated technique which combines the two most important tools in their field. A brief review of the literature describing how LC-NMR has been applied to natural products research is followed by a specific example illustrating how this technique was used to identify the marine alkaloid aaptamine (1). Aaptamine was identified as the active component in the crude dichloromethane extract of the sponge Aaptos sp. which had been determined to possess inhibitory activity against the enzyme glutamine:fructose-6-phosphate amidotransferase (GFAT) by a high throughput screening (HTS) effort. Isolated aaptamine (1) exhibited an IC50 = 120 microM against this enzyme. The experience gained from the identification of aaptamine was used to define a strategy for the use of LC-NMR in a natural products HTS program.

Mass spectrometrically detected directly coupled high performance liquid chromatography/nuclear magnetic resonance spectroscopy/mass spectrometry for the identification of xenobiotic metabolites in maize plants

Reconstructed ion chromatograms have been used to identify relevant high performance liquid chromatography (HPLC) peaks in a directly coupled high performance liquid chromatography/nuclear magnetic resonance spectroscopy/mass spectrometry (HPLC/NMR/MS) experiment. This has been applied to a study of the metabolism of a model compound, 5-nitropyridone (2-hydroxy-5-nitropyridine), in maize plants grown hydroponically. By monitoring the on-flow reconstructed ion chromatogram corresponding to the 5-nitropyridone fragment at m/z 143, and additional molecular ions corresponding to metabolites identified as products from similar compounds, relevant peaks were identified rapidly for subsequent stopped-flow 1H NMR spectroscopic analysis. The combination of coupled HPLC/NMR/MS enabled the direct identification of three metabolites, namely the N-glucoside, N-malonylglucoside, and O-malonylglucoside. This work demonstrates the power of HPLC/NMR/MS for the structural elucidation of xenobiotic metabolites in complex biological matrices (such as plant material) with minimal sample preparation. In particular, using mass spectrometry for the initial identification of relevant HPLC peaks allows the analysis of complex samples without the necessity for other spectroscopic markers, such as 19F NMR signal for fluorinated compounds or UV spectroscopy for molecules with strong UV chromophores.

Application of high-performance liquid chromatography coupled to nuclear magnetic resonance spectrometry, mass spectrometry and bioassay for the determination of active saponins from Bacopa monniera Wettst

Reversed-phase high-performance liquid chromatographic separation coupled to (structurally informative) spectroscopic methods like NMR and MS and an efficient bioassay have been used to determine the active compounds from a crude fraction of Bacopa monniera. The fraction containing a mixture of saponins with closely related structures was found to show a significant anthelmintic activity against Caenorhabditis elegans (used as a model test organism for determining anthelmintic activity). The activity was correlated to two dammarane type triterpenoidal saponins containing at least three sugar units. The optimization of separation for 1 mg of the crude sample on column and the sensitivity of on-flow one- and two-dimensional NMR experiments to the high-molecular-mass compounds (M(r) 890-930) has been demonstrated.

LC/MS applications in drug development

The combination of high-performance liquid chromatography and mass spectrometry (LC/MS) has had a significant impact on drug development over the past decade. Continual improvements in LC/MS interface technologies combined with powerful features for structure analysis, qualitative and quantitative, have resulted in a widened scope of application. These improvements coincided with breakthroughs in combinatorial chemistry, molecular biology, and an overall industry trend of accelerated development. New technologies have created a situation where the rate of sample generation far exceeds the rate of sample analysis. As a result, new paradigms for the analysis of drugs and related substances have been developed. The growth in LC/MS applications has been extensive, with retention time and molecular weight emerging as essential analytical features from drug target to product. LC/MS-based methodologies that involve automation, predictive or surrogate models, and open access systems have become a permanent fixture in the drug development landscape. An iterative cycle of "what is it?" and "how much is there?" continues to fuel the tremendous growth of LC/MS in the pharmaceutical industry. During this time, LC/MS has become widely accepted as an integral part of the drug development process. This review describes the utility of LC/MS techniques for accelerated drug development and provides a perspective on the significant changes in strategies for pharmaceutical analysis. Future applications of LC/MS technologies for accelerated drug development and emerging industry trends are also discussed.

NMR tools for biotechnology

Recent developments in NMR spectroscopy verify that NMR continues to be an exciting area of research. These advances can be placed into three general categories: new hardware; new techniques; and novel applications. The hardware developments include many advances in the area of flow NMR and some new probe designs. The new techniques include several ways to edit the NMR spectra of mixtures without using chromatographic separation. These new NMR tools are now allowing us to analyze complex mixtures, combinatorial-chemistry libraries, bound drugs, unstable compounds, very small samples, and heterogeneous samples.