Directly Coupled Chiral HPLC−NMR and HPLC−CD Spectroscopy as Complementary Methods for Structural and Enantiomeric Isomer Identification: Application to Atracurium Besylate

Flexible organic frameworks sequester neuromuscular blocking agents in vitro and reverse neuromuscular block invivo

Supramolecular sequestration and reversal of neuromuscular block (NMB) have great clinical applications. Water-soluble flexible organic frameworks (FOFs) cross-linked by disulfide bonds are designed and prepared. Different linker lengths are introduced to FOFs to give them varied pore sizes. FOFs are anionic nanoscale polymers and capable of encapsulating cationic neuromuscular blocking agents (NMBAs), including rocuronium (Roc), vecuronium (Vec), pancuronium (Panc) and cisatracurium (Cis). A host–guest study confirms that FOFs bind NMBAs in water. The multivalency interaction between FOFs and NMBAs is able to sequester NMBAs, and prevent them from escaping. These FOFs are non-toxic and biocompatible. Animal studies show that FOFs are effective for the reversal of NMB induced by Roc, Vec and Cis, which shorten the time to a train-of-four ratio of 0.9 by 2.6, 3.8 and 5.7-fold compared to a placebo, respectively.

Water-soluble flexible organic frameworks are prepared and used to sequester neuromuscular blocking agents, and reverse their neuromuscular block in vivo.

Chiral metabonomics: 1H NMR-based enantiospecific differentiation of metabolites in human urine via direct cosolvation with β-cyclodextrin

Differences in molecular chirality remain an important issue in drug metabolism and pharmacokinetics for the pharmaceutical industry and regulatory authorities, and chirality is an important feature of many endogenous metabolites. We present a method for the rapid, direct differentiation and identification of chiral drug enantiomers in human urine without pretreatment of any kind. Using the well-known anti-inflammatory chemical ibuprofen as one example, we demonstrate that the enantiomers of ibuprofen and the diastereoisomers of one of its main metabolites, the glucuronidated carboxylate derivative, can be resolved by (1)H NMR spectroscopy as a consequence of direct addition of the chiral cosolvating agent (CSA) β-cyclodextrin (βCD). This approach is simple, rapid, and robust, involves minimal sample manipulation, and does not require derivatization or purification of the sample. In addition, the method should allow the enantiodifferentiation of endogenous chiral metabolites, and this has potential value for differentiating metabolites from mammalian and microbial sources in biofluids. From these initial findings, we propose that more extensive and detailed enantiospecific metabolic profiling could be possible using CSA-NMR spectroscopy than has been previously reported.

Combining HPLC-PDA-MS-SPE-NMR with circular dichroism for complete natural product characterization in crude extracts: levorotatory gossypol in Thespesia danis

Despite recent demonstration of the power of HPLC-PDA-MS-SPE-NMR (high-performance liquid chromatography-photodiode-array detection-mass spectrometry-solid-phase extraction-nuclear magnetic resonance) in structure determination of natural products directly from minute amounts of crude extracts, this technique leaves chirality of the compounds uncharacterized. In this work we demonstrate that postcolumn SPE is a useful method of analyte concentration and accumulation not only for NMR but also for CD (circular dichroism) spectroscopy. Thus, use of HPLC-PDA-MS-SPE-NMR in combination with CD allowed rapid detection of ( R)-(-)-gossypol [( R)- 1] in Thespesia danis, providing a very rare example of the predominance of the levorotatory enantiomer of gossypol. Enantioselectivity of the in vitro antiplasmodial activity of gossypol was also demonstrated; the IC50 value of ( R)- 1 was 4.5 +/- 0.2 microM, with the eudismic ratio of about 2.5. No gossypol was detected in Gossypioides kirkii.

Combination of HPLC “Inverted Chirality Columns Approach” and MS/MS Detection for Extreme Enantiomeric Excess Determination Even in Absence of Reference Samples. Application to Camptothecin Derivatives

An original, extremely sensitive and selective HPLC-MS/MS technique for the identification and determination of the minor enantiomer in nonracemic mixtures, even when only one enantiomer is available as reference, is described. The method is based on the so-called "inverted chirality columns approach" (ICCA) and consists of the use of chiral stationary phases (CSPs) available in both enantiomeric forms: in fact, inversion of the elution order for a pair of enantiomers is observed in response to the change in column chirality. This offers two key advantages: first, it is possible to demonstrate the potential enantioselectivity of the system by generating a virtual racemate, and second, it permits the choosing of the right column chirality for trace determination. Combination with MS/MS detection affords high specificity allowing not only high sensitivity (down to 0.0025% of the minor enantiomer) but also unequivocal peak identification in complex mixtures. Applications to semisynthetic derivatives of camptothecin, endowed with antitumor activity, are reported. Moreover, applicability of ICCA is not limited to this class of molecules but generates universal support. Its use might also be extended to other classes of compounds by using other CSPs, available in both enantiomeric forms.

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.

A photometric screening method for dimeric naphthylisoquinoline alkaloids and complete on-line structural elucidation of a dimer in crude plant extracts, by the LC-MS/LC-NMR/LC-CD triad

An efficient evaluation procedure for the chemical screening and on-line structural elucidation of dimeric naphthylisoquinoline alkaloids has been developed. The method is based on the lead tetraacetate oxidation of the central binaphthalene core of the alkaloids. UV spectra of the extracts after addition of the oxidant show, in the presence of naphthylisoquinoline dimers, the appearance of a characteristic long-wavelength absorption indicative of dinaphthoquinones. The efficiency and relevance of the method has been demonstrated in the discovery of a constitutionally and configurationally new dimeric naphthylisoquinoline alkaloid, named ancistrogriffithine A (4), from the previously uninvestigated Asian liana Ancistrocladus griffithii. After verification of this screening result by LC-ESI-MS/MS, the constitution and the relative configuration of the compound were elucidated on line, by LC-NMR and LC-CD on the extract. Using an LC-NMR-WET-ROESY experiment, itwas possible for the first time to determine the relative axial configuration of a natural biaryl compound on line, by observing long-range ROE interactions. Finally, an oxidative degradation right on the extract delivered the absolute configuration of 4, without isolation of the alkaloid. Ancistrogriffithine A is the as yet only dimeric naphthylisoquinoline from an Asian Ancistrocladaceae plant.

High-performance liquid chromatography interfaced with fluorescence line-narrowing spectroscopy for on-line analysis

We have demonstrated, for the first time, that high-performance liquid chromatography (HPLC) can be interfaced with fluorescence line-narrowing spectroscopy (FLNS) for on-line identification and characterization of analytes. Interfacing centered primarily on the design and construction of a novel liquid helium cryostat that accommodates variable-sized quartz tubes/capillaries suitable for HPLC as well as capillary electrophoresis/electrochromatography. In addition to the high spectral resolution afforded by FLNS, analyzing the separated components at 4.2 K minimizes photodegradation from the excitation source and provides indefinite detection times for signal averaging. The proof-of-principle for the HPLC-FLNS system is first demonstrated with a mixture of four structurally similar polycyclic aromatic hydrocarbons and then applied to the analysis of DNA adducts from mouse skin exposed to the carcinogen dibenzo[a,l]pyrene. With femtomole detection limits, HPLC-FLNS can be used for real-world analyses of complex mixtures.

Identification of autoxidation and photodegradation products of ethynylestradiol by on-line HPLC-NMR and HPLC-S

HPLC-NMR, HPLC-MS, and HPLC-UV were used to characterize the predominant solution autoxidation and photodegradation products of ethynylestradiol (1). A hydroperoxide (2) and a series of isomeric dimeric oxidation products (3-7), were identified.

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.

Case of enantiomer impurity identification by normal-phase chiral high-performance liquid chromatography with optical rotation and mass spectrometric detection

An impurity produced in the synthesis of compound I is separated and identified as its enantiomer II using normal-phase chiral high-performance liquid chromatography (HPLC) with UV absorbance, optical rotation (OR) and mass spectrometric (MS) detection. The results show that the impurity II and compound I have equal and opposite specific rotations, identical MS spectra and the same MS-MS fragmentation pattern, as required for enantiomers. The procedures presented demonstrate a novel combination of methods for enantiomer identification and characterization that do not require the preparation of individual enantiomer markers or even the racemic mixture, thus reducing the need for additional synthetic work.

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.