Differentiation of three pairs of aconite alkaloid isomers from Aconitum nagarum var. lasiandrum by electrospray ionization tandem mass spectrometry

A systematic review of pharmacological activities, toxicological mechanisms and pharmacokinetic studies on Aconitum alkaloids

The tubers and roots of Aconitum (Ranunculaceae) are widely used as heart medicine or analgesic agents for the treatment of coronary heart disease, chronic heart failure, rheumatoid arthritis and neuropathic pain since ancient times. As a type of natural products mainly extracted from Aconitum plants, Aconitum alkaloids have complex chemical structures and exert remarkable biological activity, which are mainly responsible for significant effects of Aconitum plants. The present review is to summarize the progress of the pharmacological, toxicological, and pharmacokinetic studies of Aconitum alkaloids, so as to provide evidence for better clinical application. Research data concerning pharmacological, toxicological and pharmacokinetic studies of Aconitum alkaloids were collected from different scientific databases (PubMed, CNKI, Google Scholar, Baidu Scholar, and Web of Science) using the phrase Aconitum alkaloids, as well as generic synonyms. Aconitum alkaloids are both bioactive compounds and toxic ingredients in Aconitum plants. They produce a wide range of pharmacological activities, including protecting the cardiovascular system, nervous system, and immune system and anti-cancer effects. Notably, Aconitum alkaloids also exert strong cardiac toxicity, neurotoxicity and liver toxicity, which are supported by clinical studies. Finally, pharmacokinetic studies indicated that cytochrome P450 proteins (CYPs) and efflux transporters (ETs) are closely related to the low bioavailability of Aconitum alkaloids and play an important role in their metabolism and detoxification in vivo.

Chemical constituents in different parts of seven species of Aconitum based on UHPLC-Q-TOF/MS

Aconitum L., the main source of Aconitum medicinal materials, is rich in diterpenoid alkaloids. Several drugs derived from diterpenoid alkaloids are widely used to the current clinical treatment of pain, inflammation, and other symptoms. This paper aims to clarify the main metabolites and distribution of diterpenoid alkaloids in different parts of Aconitum plants. To that end, 7 species of Aconitum from three subgenera were analyzed by UHPLC-Q-TOF-MS under identical conditions. The fragmentation regularity of various types of diterpene alkaloids were determined and a total of 126 metabolites were identified by comparing the reference material and secondary mass spectrometry, with the literature. 67, 49, 17, 41, 14, 17 and 21 metabolites were identified from Aconitum carmichaeli, Aconitum stylosum, Aconitum sinomontanum, Aconitum vilmorinianum, Aconitum pendulum, Aconitum tanguticum and Aconitum gymnandrum, respectively. Meanwhile, the structure type of A. carmichaeli, A. stylosum, A. vilmorinianum, A. pendulum, A. gymnandrum were identified as C₁₉ type, A. sinomontanum was C₁₈ type, while A. tanguticum was C₂₀ type. A high similarity of metabolites was found between A. stylosum and A. vilmorinianum. The quantitative analysis of 19 compounds and the relative peak area of all metabolites which obtained through internal standard berberine, highlighted compounds like karakoline, talatisamine and atisine as references for future study of metabolic pathways. Furthermore, results from metabolites distribution and relative peak area analysis suggest that the leaf of A. carmichaeli, the leaf and stem of A. stylosum and A. vilmorinianum, and the flower of A. pendulum have potential as medicinal resources and are worth further development. These results establish a foundation for the comprehensive utilization of Aconitum resources.

A Fragmentation Study on Four Oligostilbenes by Electrospray Tandem Mass Spectrometry

Oligostilbenes have attracted much interest due to their intricate structures and diverse bioactivities. In this study, two stilbene dimers, (-)-7,8-cis-ε-viniferin (1) and carasiphenol A (2), and two trimers, suffruticosol A (3) and suffruticosol C (4), were investigated by electrospray ionization ion-trap time-of-flight multistage mass spectrometry (ESI-IT-TOF-MSⁿ). Based on the MSⁿ study, the fragmentation pathways and diagnostic ions of four oligostilbenes in both positive and negative modes were proposed. The consecutive elimination of phenol (C₆H₆O) and resorcinol (C₆H₆O₂) moieties were the particular dissociation for oligostilbenes due to the presence of 1,2-diphenylethylene nucleus. The present MSⁿ fragmentation study will provide valuable information for the fast characterization of oligostilbenes from complicated natural mixtures.

Localization of malonyl and acetyl on substituted saikosaponins according to the full-scan mass spectra and the fragmentation of sodium-adduct ions in the positive mode

RATIONALE

Discriminating between aglycone-substituted and saccharide-substituted saikosaponins by liquid chromatography/tandem mass spectrometry (LC/MSⁿ ) is a long-standing issue that is still to be resolved. It is necessary to characterize the two types of substituted saikosaponins taking into consideration the potential significant difference in their bioactivity.

METHODS

Taking the substituents malonyl and acetyl as examples, we developed a MS strategy to discriminate between the aglycone-substituted and saccharide-substituted saikosaponins through comparing their Y₀  - nH₂ O (n = 1-2) ions from the protonated molecules in the full-scan mass spectra and their B ions in the MS² spectra of sodium-adduct molecules in the positive mode.

RESULTS

The deprotonated molecules of the aglycone-substituted saikosaponins presented similar fragmentation patterns to those of saccharide-substituted ones in the negative mode, which could not discriminate whether the substitutes were located on the aglycone or the saccharide. In contrast, the Y₀  - nH₂ O (n = 1-2) ions containing or no substituent were observed respectively in the mass fragmentation of the protonated molecules of aglycone-substituted or saccharide-substituted saikosaponins in the positive mode. In addition, the B ions containing or no substituent were observed respectively in the mass fragmentation of the sodium-adduct molecules of the saccharide-substituted or aglycone-substituted saikosaponins in the positive mode. Two aglycone-malonylated saikosaponins were reported for the first time.

CONCLUSIONS

Whether the substituents were located on the aglycone or the saccharide could be determined according to the Y₀  - nH₂ O (n = 1-2) ions from the protonated molecules in the full-scan mass spectra and the B ions in the MS² spectra of sodium-adduct molecules in the positive mode. Our results have updated the mass fragmentation patterns of substituted saikosaponins, which is helpful for the quality control of pharmaceutical preparations containing saikosaponins. More importantly, this MS strategy should be able to be extended to characterize other substituted saponins of bioactive significance in future studies.

A Fragmentation Study on Four Unusual Secoiridoid Trimers, Swerilactones H-K, by Electrospray Tandem Mass Spectrometry

Swerilactones H-K (1-4) as four unprecedented secoiridoid trimers represent a new type of natural product, which has attracted much interest of natural chemists due to their novel skeletons and promising bioactivity. In order to well understand their MS fragmentation behaviors, they were investigated by electrospray ionization ion-trap time-of-flight multistage product ion mass spectrometry (ESI-IT-TOF-MS ⁿ ) for the first time. The protonated molecules ([M+H]⁺) of swerilactones J and K, and deprotonated molecules ([M-H]^-) of swerilactones H, J and K were readily observed in the conventional single-stage mass spectra (MS); however only the [M+Cl]^- ion for swerilactone I was obtained in negative mode. Based on the MS ⁿ study, the fragmentation pathways of swerilactones H and I in negative mode, and swerilactones J and K in both positive and negative modes were proposed. The neutral losses of H₂O, CO, CO₂ and C₂H₄O moieties are the particular elimination from the precursor ions due to the presence of hydroxyl, δ-lactone and 1-O-ethyl moieties in their structures, of which the retro-Diels-Alder cleavage was the most particular dissociation. The fragment ions at m/z 341 and 291 in negative mode can be considered as the diagnostic ions for secoiridoid trimers. This investigation will provide valuable information for their fast characterization from complicated natural mixtures and extensive understanding their structural architectures.

Study on the Alkaloids in Tibetan Medicine Aconitum pendulum Busch by HPLC-MSn Combined with Column Chromatography

A rapid, convenient and effective identification method of alkaloids was established and an attempt on isolating and analyzing the alkaloids in Aconitum pendulum Busch was conducted successfully. In this article, four high-content components including deoxyaconitine, benzoylaconine, aconine and neoline were isolated by using column chromatography. HPLC-MS(n)was employed to deduce the regulations of fragmentation of diterpenoid alkaloids which displayed a characteristic behavior of loss of CO(28u), CH3COOH(60u), CH3OH(32u), H2O(18u) and C6H5COOH(122u). Then, according to fragmentation regulation of mass spectrometry, 42 alkaloids were found inA. pendulum Among them, 38 compounds were identified and 29 alkaloids were reported for the first time for this herb. Therefore, this means that HPLC-MS(n)combined with column chromatography could work as an effective and reliable tool for rapid identification of the chemical components of herbal medicine.

Fragmentation reactions using electrospray ionization mass spectrometry: an important tool for the structural elucidation and characterization of synthetic and natural products

Over the last decade, the number of studies reporting the use of electrospray ionization mass spectrometry (ESI-MS) in combination with collision cells (or other activation methods) to promote fragmentation of synthetic and natural products for structural elucidation purposes has considerably increased. However, the lack of a systematic compilation of the gas-phase fragmentation reactions subjected to ESI-MS/MS conditions still represents a challenge and has led to many misunderstood results in the literature. This review article exploits the most common fragmentation reactions for ions generated by ESI in positive and negative modes using collision cells in an effort to stimulate the use of this technique by non-specialists, undergraduate students and researchers in related areas.

A fragmentation study on four C19-diterpenoid alkaloids by electrospray ionization ion-trap time-of-flight tandem mass spectrometry

High-resolution electrospray ionization ion-trap time-of-flight tandem mass spectrometry (HR-ESI-IT-TOF-MS(n)) in positive-ion mode was used to determine the accurate masses and fragmentation pathways of four C(19)-diterpenoid alkaloids, aconitine (1), yunnaconitine (2), crassicauline A (3), and benzoylmesaconine (4). The [M+H](+) ions of compounds 1-4 were readily observed in conventional single-stage mass spectrometry. Based on the MS(1-6) analyses, detailed fragmentation rules of the four compounds were proposed. The neutral losses of AcOH, MeOH, H(2)O, CO, C(2)H(4), PhCOOH and p-OMePhCOOH segments were the characteristic eliminations from the precursor ions due to the presence of acetyl, methoxyl, hydroxyl, N-ethyl, benzoyl and p-methoxyl-benzoyl units in the structures. Benefited from the high resolution of the mass analyzer, the loss of 28 Da corresponding to CO or CH(4) segment in product ions was unambiguously distinguished. The losing sequence of the main substituent groups was summarized as: C(8)-acetyl>C(16)-methotyl>C(15)-hydroxyl>C(6)-methoxyl>C(1)-methoxyl/C(3)-hydroxyl>C(18)-methoxyl>>C(13)-hydroxyl. The sequential loss of (16)-methoxyl moiety and CO (generating from enol-ketone tautomerism) groups could be recognized as the characteristic eliminations for the compounds with C(16)-methoxyl and C(15)-hydroxyl groups simultaneously. The application of HR-ESI-IT-TOF-MS(n) technique to investigate the fragmentation of C(19)-diterpenoid alkaloids provided useful information to understand their fragmentation behaviors.

Rapid differentiation of ortho-, meta-, and para-isomers of halogenated phenylmethylidene hydrazinecarbodithioates by metal complexation and electrospray ionization mass spectrometry

RATIONALE

Development of mass spectrometry (MS)-based methods for isomeric differentiation remains a challenging analytical task, and has attracted the interest of many research groups. It is relevant to develop a general method to differentiate the isomeric halogenated phenylmethylidene hydrazinecarbodithioates (MX, X  =  F, Cl, Br).

METHODS

Diluted CH3 CN solutions containing NiCl2 and a title isomer (MX) were analyzed by electrospray ionization tandem mass spectrometry (ESI-MS(n)) in a quadrupole ion trap instrument equipped with an ESI source. Theoretical calculations were performed using the density functional theory (DFT) method at the uB3LYP/6-31+G(2d,p) level.

RESULTS

In MS(3) experiments, the complex [MX + SCH3 + Ni](+) ion, resulting from dissociation of the ESI-generated complex [2MX - H + Ni](+) ion, undergoes ligand-exchange reactions with residual gas molecules, such as water, acetonitrile, and nitrogen in the ion trap, and the o-isomers [Mo-X + SCH3 + Ni](+) were found to undergo the characteristic HX elimination reactions to afford several unique ions. Each set of three isomers [MX + SCH3 + Ni](+) show significantly different reactivity, which has been corroborated by MS(4) experiments and theoretical calculations.

CONCLUSIONS

A rapid method based on metal complexation and tandem mass spectrometric (MS(n)) analysis has been developed to differentiate three sets of positional isomers of halogenated phenylmethylidene hydrazinecarbodithioates (MX, X =  F, Cl, Br).

Neutral fragment filtering for rapid identification of new diester-diterpenoid alkaloids in roots of Aconitum carmichaeli by ultra-high-pressure liquid chromatography coupled with linear ion trap-orbitrap mass spectrometry

A rapid and effective method was developed for separation and identification of diester-diterpenoid alkaloids (DDA) in the roots of Aconitum carmichaeli by ultra-high-pressure liquid chromatography coupled with high resolution LTQ-Orbitrap tandem mass spectrometry (UHPLC-LTQ-Orbitrap-MSⁿ). According to accurate mass measurement and the characteristic neutral loss filtering strategy, a total of 42 diester-diterpenoid alkaloids (DDA) were rapidly detected and characterized or tentatively identified. Meanwhile, the proposed fragmentation pathways and the major diagnostic fragment ions of aconitine, mesaconitine and hypaconitine were investigated to trace DDA derivatives in crude plant extracts. 23 potential new compounds were successfully screened and characterized in Aconitum carmichaeli, including 16 short chain fatty acyls DDA, 4 N-dealkyl DDA and several isomers of aconitine, mesaconitine and hypaconitine.

Characterization of physalins and fingerprint analysis for the quality evaluation of Physalis alkekengi L. var. franchetii by ultra-performance liquid chromatography combined with diode array detection and electrospray ionization tandem mass spectrometry

Physalins are important bioactive compounds from genus Physalis. They often occur as isomers, which makes the structural elucidation difficult. In the present study, the fragmentation behavior and UV characteristics of seven physalins from genus Physalis were firstly investigated using electrospray ionization tandem mass spectrometry (ESI-MS/MS) and diode array detection (DAD). Combined with ultra-performance liquid chromatography (UPLC) and DAD, the established approach to the structural identification of physalins by ESI-MS/MS was then applied to the analysis of Physalis alkekengi L. According to the UPLC retention behavior, the diagnostic UV spectra and the molecular structural information provided by MS/MS spectra, about 19 fingerprint peaks were identified, including 14 physalins and 5 other compounds. Finally, the established fingerprint method was applied to the analysis of 31 P. alkekengi L. samples collected from different locations, which reflected their similar chemical constituent properties. The proposed method provides a scientific and technical platform to the herbal industry for quality control and safety assurance of herbal preparations that contain this class of physalins.

Liquid chromatography coupled with time-of-flight and ion trap mass spectrometry for qualitative analysis of herbal medicines

With the expansion of herbal medicine (HM) market, the issue on how to apply up-to-date analytical tools on qualitative analysis of HMs to assure their quality, safety and efficacy has been arousing great attention. Due to its inherent characteristics of accurate mass measurements and multiple stages analysis, the integrated strategy of liquid chromatography (LC) coupled with time-of-flight mass spectrometry (TOF-MS) and ion trap mass spectrometry (IT-MS) is well-suited to be performed as qualitative analysis tool in this field. The purpose of this review is to provide an overview on the potential of this integrated strategy, including the review of general features of LC-IT-MS and LC-TOF-MS, the advantages of their combination, the common procedures for structure elucidation, the potential of LC-hybrid-IT-TOF/MS and also the summary and discussion of the applications of the integrated strategy for HM qualitative analysis (2006-2011). The advantages and future developments of LC coupled with IT and TOF-MS are highlighted.

Diastereomeric differentiation of norbornene amino acid peptides by electrospray ionization tandem mass spectrometry

A new class of diastereomeric pairs of non-natural amino acid peptides derived from butyloxycarbonyl (Boc-)protected cis-(2S,3R)- and trans-(2S,3S)-beta-norbornene amino acids including a monomeric pair have been investigated by electrospray ionization (ESI) tandem mass spectrometry using quadrupole time-of-flight (Q-TOF) and ion-trap mass spectrometers. The protonated cis-BocN-beta-nbaa (2S,3R) (1) (betanbaa = beta-norbornene amino acid) eliminates the Boc group to form [M+H-Boc+H](+), whereas an additional ion [M+H-C(4)H(8)](+) is formed from trans-BocN-beta-nbaa (2S,3S) (2). Similarly, it is observed that the peptide diastereomers (di-, tri- and tetra-), with cis-BocN-beta-nbaa (2S,3R)- at the N-terminus, initially eliminate the Boc group to form [M+H-Boc+H](+) which undergo further fragmentation to give a set of product ions that are different for the peptides with trans-BocN-beta-nbaa (2S,3S)- at the N-terminus. Thus the Boc group fragments differently depending on the configuration of the amino acid present at the N-terminus. It is also observed that the peptide bond cleavage in these peptides is less favoured and most of the product ions are formed due to retro-Diels-Alder fragmentation. Interestingly, sodium-cationized peptide diastereomers mainly yield a series of retro-Diels-Alder fragment ions which are different for each diastereomer as they are formed starting from [M+Na-Boc+H](+) in peptides with cis-BocN-beta-nbaa (2S,3R)- at the N-terminus, and [M+Na-C(4)H(8)](+) in peptides with trans-BocN-beta-nbaa (2S,3S)- at the N-terminus. All these results clearly indicate that these diastereomeric pairs of peptides yield characteristic product ions which help distinguish the isomers.

Study of the characteristic fragmentation behavior of hydroquinone glycosides by electrospray ionization tandem mass spectrometry with optimization of collision energy

The fragmentation behavior of hydroquinone glycosides involving one or two sugar groups from Fraxinus sieboldiana and their analogue arbutin was investigated systematically by electrospray ionization tandem mass spectrometry in negative ion mode. The characteristic fragmentation reaction of these compounds was through the homolytic and heterolytic cleavage of the O-glycosidic bond to produce radical aglycone ion ([Y0-H]-*) and aglycone ion (Y0-), respectively. Unambiguous differentiation between the mono-O-glycoside isomers which differ in glycosylation position was achieved by comparing the relative abundance of [Y0-H]-* and Y0- ions with the optimized collision energy. In the fragmentation of 1, 4-di-O-glycosides, only the Y0- ion was produced when the first glucosyl residue was expelled. However, both the [Y0-H]-* and Y0- ions were present when the second glucosyl residue was eliminated. In addition, an interesting [Y0-2H]- ion was present in the product ion spectra of hydroquinone glycosides with methoxy group(s) substituted at C-3 or/and C-5 positions of the benzene ring. The results of this study can facilitate the rapid determination of hydroquinone glycosides in crude plant extracts and also reveal that the systematic investigation and optimization of collision energy play an important role in the differentiation of isomers which have subtle differences in structures.

Structural characterization and identification of C(19)- and C(20)-diterpenoid alkaloids in roots of Aconitum carmichaeli by rapid-resolution liquid chromatography coupled with time-of-flight mass spectrometry

Aconite alkaloids from the roots of Aconitum carmichaeli (Fuzi, in Chinese) have been investigated by rapid-resolution liquid chromatography coupled with time-of-flight mass spectrometry (TOFMS) in positive mode. With dynamic adjustment of the key role as fragmentor voltage in TOFMS, an efficient transmission of the ions was achieved to obtain the best sensitivity for providing the molecular formula for each analyte, and abundant fragment ions for structural information. Fifteen authentic standards isolated from Fuzi with various structures were first characterized by TOFMS, including diester-diterpenoid alkaloids (DDAs), monoester-diterpenoid alkaloids (MDAs), alkylol amine-diterpenoid alkaloids (ADAs), veatchine-type alkaloids and atisine-type alkaloids. Fragmentation rules and key diagnostic fragment ions have been summarized, and possible pathways of fragmentation have been proposed. By accurate mass measurements within 5 ppm error for each ion, 30 C(19)-diterpenoid alkaloids including 10 DDAs, 3 MDAs, 9 ADAs and 8 other type alkaloids, and 8 C(20)-diterpenoid alkaloids including 4 veatchine-type alkaloids and 4 atisine-type alkaloids could be identified in a methanolic extract of Fuzi. Some isomers of aconite alkaloids were also differentiated. Based on the differences between their fragmentation pathways and special fragment ions, each type of aconite alkaloids was differentiated.

Characterization and identification of isomeric flavonoid O-diglycosides from genus Citrus in negative electrospray ionization by ion trap mass spectrometry and time-of-flight mass spectrometry

Flavonoid O-diglycosides are important bioactive compounds from genus Citrus. They often occur as isomers, which makes the structural elucidation difficult. In the present study, the fragmentation behavior of six flavonoid O-diglycosides from genus Citrus was investigated using ion trap mass spectrometry in negative electrospray ionization (ESI) with loop injection. For the flavonoid O-rutinosides, [M-H-308]- ion was typically observed in the MS2 spectrum, suggesting the loss of a rutinose. The fragmentation patterns of flavonoid O-neohesperidosides were more complicated in comparison with their rutinoside analogues. A major difference was found in the [M-H-120]- ion in the MS2 spectrum, which was a common feature of all the flavonoid O-neohesperidosides. The previous literature for naringin located the loss of 120Da to the glycan part, whereas the present study for naringin had shown that the [M-H-120]- ion was produced by a retro-Diels-Alder reaction in ring C, and this fragmentation pattern was confirmed by the accurate mass measurement using an orthogonal time-of-flight mass spectrometer. Combined with high performance liquid chromatography (HPLC) and diode array detection (DAD), the established approach to the structural identification of flavonoid O-diglycosides by ion trap mass spectrometry was applied to the analysis of extracts of two Chinese medicines derived from genus Citrus, namely Fructus aurantii and F. aurantii immaturus. According to the HPLC retention behavior, the diagnostic UV spectra and the molecular structural information provided by multistage mass spectrometry (MS(n)) spectra, 13 flavonoid O-glycosides in F. aurantii and 12 flavonoid O-glycosides in F. a. immaturus were identified rapidly.

Analysis of sodium adduct paeoniflorin, albiflorin and their derivatives by (+)ESI-MSn, DFT calculations and computer-aided mass spectrometry analysis program

In order to analyze paeoniflorin, albiflorin and their derivatives (PADs) in Paeonia Lactiflora rapidly and effectively, (+)ESI-MS(n) experiments were conducted, from which two diagnostic fragment patterns were acquired. Meanwhile, the dehydration ability of aglycones of PADs was obtained by calculating their activation energy using density functional theory, through which the unique dehydration phenomenon of benzoylalbiflorin, compared with benzoylpaeoniflorin, was interpreted. In addition, a computer-aided mass spectrometry analysis program was developed to facilitate the analysis of the unknown compound by suggesting the possible structure of the analyte.

Tunable transition metal-ligand complexation for enhanced elucidation of flavonoid diglycosides by electrospray ionization mass spectrometry

A tunable ESI-MS/MS strategy for differentiation of flavone and flavanone diglycoside isomers based on metal complexation with auxiliary ligands is reported. The addition of a metal salt and an auxiliary ligand to a flavonoid solution results in the formation of [M(II) (flavonoid-H) auxiliary ligand](+) complexes, where M(II) is a transition metal. A series of auxiliary ligands with electron-withdrawing substituents were synthesized to tailor the relative metal binding affinities of the ligands and thus directly influence the stabilities, and consequently the dissociation pathways, of the complexes. Upon collisionally activated dissociation, the complexes yield fragmentation patterns in which the abundances of key diagnostic ions are enhanced, thus facilitating isomer differentiation.