Ionization Multi-stage Tandem Mass Spectrometry Research Articles

Studies of iridoid glycosides using liquid chromatography/electrospray ionization tandem mass spectrometry

Fragmentation pathways of five iridoid glycosides have been studied by using electrospray ionization multi-stage tandem mass spectrometry (ESI-MS(n)). The first-stage MS data of the five iridoid glycosides were compared. The MS spectra showed that the adduct ions of iridoid glycosides and the formate anion were diagnostic ions to distinguish iridoid glycosides with a carboxyl group at the C-4 position or an ester group at the C-4 position. The MS fragmentation pathways of the five iridoid glycosides were also studied. Analyzing the product ion spectra of iridoid glycosides, some neutral losses were observed, such as H(2)O, CO(2) and glucose residues, which were very useful for the identification of the functional groups in the structures of iridoid glycosides. Furthermore, specific loss of one molecule of methyl 3-oxopropanoate or 3-oxopropanic acid was firstly discussed, which corresponded to the isomerization of the hemiacetal group in the structure of iridoid aglycone. According to the fragmentation mechanisms and HPLC/MS(n) data, the structures of five iridoid glycosides in a crude extract of Gardenia jasminoisdes fruit have been identified. Three compounds were compared with standards and the other two were identified as shanzhiside and genipin gentibioside by their MS(n) data without standard compounds. In order to further validate the veracity of the deduction, genipin gentiobioside was isolated from the extract of Gardenia jasminoisdes fruit using Purification Factory and was further identified by C- and H-NMR.

A fragmentation study of podophyllotoxin and its 4′‐demethyl‐4β‐substituted derivatives by electrospray ionization ion‐trap time‐of‐flight tandem mass spectrometry

High-resolution electrospray ionization multistage tandem mass spectrometry (MS(1-9)) was used to determine the accurate masses and the fragmentation pathways of protonated podophyllotoxin (1) and its corresponding 4'-demethyl-4beta-substituted derivatives (2-4). The protonated molecules, [M + H](+), of all the four compounds were observed in the conventional single-stage mass spectra. Two fragmentation pathways, that appear to be characteristic of the four compounds, are proposed on the basis of their multistage tandem mass spectrometric data. The characteristic elimination, from the precursor protonated ions, of the neutral groups 4-R(1)H, 1-ArH, CO, CH(2)O and C(4)H(4)O(2), in which R is located on C-4, is the common elimination, and the product ions at m/z 267, 239, 229, 181, 173, 153, 143 and 115 are the common diagnostic masses. The elimination of the R(1) group substituent located on the C-4 position of compounds 1-4 has a significant influence on the fragmentation pathway obtained in the conventional single-stage mass spectra. A large R(1) group would be unfavorable for this elimination, unless the collision energy is raised. Apart from the common fragmentations obtained for the protonated molecules 1-4, significant additional product ions were detected in the various multistage tandem mass spectrometric analyses, particularly in the case of the product ions derived initially from the phenolic hydroxyl group of 2-4, which are different from those of 1. Based on these additional formed product ions, several additional fragmentation pathways for 1 or 2-4 are also presented.

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.

Electrospray ionization‐multistage tandem mass spectrometry of complex multitin organometallic compounds

The series of 14 complex organotin(IV) compounds containing many tin atoms and noncovalent bonds in the structure was characterized by electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). The mass spectra were measured in both polarity modes to obtain complementary structural information. The characteristic pattern of ten natural tin isotopes allowed the determination of the number of tin atoms in the molecular adducts and fragment ions by comparing theoretical and experimental isotopic distributions. Positive ion ESI spectra show unusual adduct formation depending on the type of organic solvent used for the direct infusion analysis owing to the ion-molecule reactions in the ion source. On the basis of the detailed spectral interpretation of organotin(IV) compounds, the fragmentation patterns of multitin organometallic compounds have been proposed. Noncovalent bonds in polymeric complexes are fragmented first, which is then followed by characteristic neutral losses in monomeric units.

Rapid structural characterization of isomeric benzo[c]phenanthridine alkaloids from the roots of Zanthoxylum nitidium by liquid chromatography combined with electrospray ionization tandem mass spectrometry

The fragmentation mechanism of six alkaloids, namely: dihydronitidine, dihydrochelerythrine, 8-acetonyldihydronitidine, 8-acetonyldrochelerythrine, nitidine and 1,3-bis(8-dihydronitidinyl)acetone, was investigated by electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn). Tandem mass spectrometry experiments indicated that different substitution sites of the methoxyl groups at C-9 and C-10 or at C-10 and C-11 determined the different abundances of the MS2 fragmentation ions using the same collision energy. According to the different abundances of MS2 product ions, positional isomeric benzo[c]phenanthridine alkaloids can be differentiated. Moreover, ten constituents in the crude alkaloidol extract from the roots of Zanthoxylum nitidium were rapidly identified by high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC/MSn), through comparing the retention times and ESI-MSn spectra with the authentic standards. This work demonstrates that not only the characteristic fragments but also the characteristic abundances of the fragment ions can be used for detailed structural characterization.

Rapid identification of C21 steroidal saponins in Cynanchum versicolor Bunge by electrospray ionization multi‐stage tandem mass spectrometry and liquid chromatography/tandem mass spectrometry

Electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn) and liquid chromatography coupled with on-line electrospray ionization tandem mass spectrometry (LC/ESI-MSn) were performed to elucidate the clearage rule of nine investigated C21 steroidal saponins and identify them in the saponin fraction of 90% ethanolic extracts from the root and rhizome of Cynanchum versicolor Bunge. The fragments of C21 steroidal saponins in positive and negative ESI-MSn were used to deduce their mass spectral fragmentation mechanisms, and their structures were further confirmed by ESI-MSn in positive mode. The MSn spectra of the [M+Na]+ ions for saponins provided a wealth of structural information on glycosidic bond cleavage, which allowed a straightforward interpretation of spectra, with respect to the identifications of features such as the sequences of sugars attached to saponins and sugar type. By using LC/ESI-MSn, nine C21 steroidal saponins were detected in the saponin fraction of C. versicolor, and an isomer of atratoglaucoside A was elucidated simultaneously. All nine compounds showed an abundant ion for the loss of 46 Da (HCOOH) from [M+Na]+. The losses of monosaccharide sequences and aglycone as neutral fragmentation from [M+Na-HCOOH]+ were also acquired as the characteristic ions of these C21 steroidal saponins. It provided important information on monosaccharide sequences and in particular on sugar types and could be used to identify and elucidate other C21 steroidal saponins. These studies allowed us to rapidly identify C21 steroidal saponins from Radix cynanchi atrati. It is indicated that the described method had wide applicability to rapidly screen and provide structural confirmation on C21 steroidal saponins in crude materials.

Electrospray tandem mass spectrometric investigations of tadalafil and its analogue

Electrospray tandem mass spectrometric investigations of tadalafil and its analogue

The Influences of A Nitrogen Atom Position in Dinucleoside 2-,3-,4-Pyridylphosphonates on Fragmentation Patterns in Electrospray Ionization Multistage Tandem Mass Spectra

2-,3-,4-Pyridylphosphonates and their phosphonothioate congeners were analyzed by electrospray ionization multistage tandem mass spectrometry (ESI-MSn). It was found that the fragmentation pathways of these compounds were not influenced to any detectable extent by the stereochemistry at the phosphorus centers but were sensitive to the position of a nitrogen atom in the pyridine ring of these compounds. Possible mechanisms for fragmentations of the investigated compounds are discussed in detail. In honor and celebration of the life and career of John A. Montgomery.

Tandem Mass Spectrometric Analysis of a Complex Triterpene Saponin Mixture of Chenopodium quinoa

A nano-HPLC electrospray ionization multi-stage tandem mass spectrometry (nLC-ESI-MS/MS) approach was applied to a complex crude triterpene saponin extract of Chenopodium quinoa seed coats. In ESI-MS/MS spectra of triterpene saponins, characteristic fragmentation reactions are observed and allow the determination of aglycones, saccharide sequences, compositions, and branching. Fragmentation of aglycones provided further structural information. The chemical complexity of the mixture was resolved by a complete profiling. Eighty-seven triterpene saponins comprising 19 reported and 68 novel components were identified and studied by MS. In addition to four reported, five novel triterpene aglycones were detected and characterized according to their fragmentation reactions in ESI-MS/MS and electron ionization mass spectrometry (EI-MS). As a novelty fragmentation pathways were proposed and analyzed based upon quantum chemical calculations using a hybrid Hartree-Fock density functional method. Accuracy of the assignment procedure was proven by isolation and structure determination of a novel compound. As the relative distribution and composition of saponins varies between different cultivars and soils, the presented strategy allows a rapid and complete analysis of Chenopodium quinoa saponin distribution and composition, and is particularly suitable for quality control and screening of extracts designated for pharmaceutical, agricultural, and industrial applications.

Structure Identification of a Prenylflavonol Glycoside from Epimedium koreanum by Electrospray Ionization Tandem Mass Spectrometry

A novel prenylflavonol glycoside, named acetylicariin, has been isolated from the aerial parts of Epimedium koreanum Nakai. The structure has been identified by electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn) and other chemical evidence, which has been elucidated as 8-prenylkaempferol-4'-methoxyl-3-O-alpha-L-rhamnopyranosyl-7-O-beta-D-(2"-O-acetyl)glucopyranoside.

Characterization of triterpenoidic saponin mixture in crude extracts from leaves of Acanthopanax senticosus Harms by saponin structural correlation and mass spectrometry

Eighteen triterpenoidic saponins in crude extracts from leaves of Acanthopanax senticous Harms have been investigated by electrospray ionization multi-stage tandem mass spectrometry and high-resolution mass spectrometry. In ESI-MS spectra, predominant [M + Na] + ions in the positive ion mode have been observed for molecular mass information. Meanwhile, specific structural correlations between these ions are firstly found. The 18 peaks (ions) can be classified into three groups (group D, E, and F with mass increase) with each group including six peaks. There is a mass difference of 132 Da between group D and E for each corresponding peak in turn (for example peak 1 to peak 7), indicating one more pentose residue was attached to saponins in group E than those corresponding in group D. The mass difference of 146 Da between group E and F implies one more deoxy-hexose attached to saponins in group F than those corresponding in group E. The structural correlations of the corresponding ions are confirmed by tandem mass spectrometry and high-resolution mass spectrometry. These structural features can not only facilitate the rapid characterization of the native known saponins in crude plant extracts, thus avoiding tedious derivation and separation of saponins, but also help find novel compounds of the same type in a specific medicinal plant. The structures of 14 known triterpenoidic saponins and four unknown saponins are thus determined or predicted. This methodology, with a combination of structural correlation of a complex mixture of homologs (which are difficult to separate) and mass spectrometry, has been established as a powerful and practical tool for the profiling of mixtures, especially of crude plant extracts and structural characterization of unknown compounds.

Rapid structural characterization of triterpenoid saponins in crude extract from S ymplocos chinensis using liquid chromatography combined with electrospray ionization tandem mass spectrometry

Triterpenoid saponins in bioactive crude extract from S ymplocos chinensis were rapidly identified using electrospray ionization multi-stage tandem mass spectrometry (ESI–MS n ) and liquid chromatography coupled with sequential mass spectrometry (LC–MS n ). According to the characteristic fragmentation behavior of known glucuronide-type triterpenoid saponins isolated from this plant, a total of fourteen constituents in the crude extract were structurally characterized on the basis of their retention time and tandem mass spectrometric analysis, including five pairs of naturally occurring isomers. Except one known saponin formerly obtained, the other constituents were new compounds. The analytical method of LC–MS n combined with ESI–MS n in positive and negative ion modes has been developed for the direct structural elucidation of triterpenoid saponins of this kind in plant extracts.

Studies on the flavones using liquid chromatography–electrospray ionization tandem mass spectrometry

Fragmentation pathways of nine flavone compounds have been studied by using electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn). Analyzing the product ion spectra of flavonoids and aglycones, we observed some diagnostic neutral losses, such as CH3, H2O, residue of glucose and gluconic acid, which are very useful for the identification of the functional groups in the structures. Furthermore, specific retro Diels-Alder (RDA) fragments for flavones with different hydroxyl substitution have also been discussed. The information is helpful for the rapid identification of the location site of hydroxyl substitution on flavones. Fragmentation pathways of C-glycosidic flavonoid have also been discussed using ESI-MSn, demonstrating ions [MH-60]−, [MH-90]−, [MH-120]− are characteristic ions of C-glycosidic flavonoid. According to the fragmentation mechanism of mass spectrometry and HPLC–MS data, the structures of seven flavones in Scutellaria baicalensis Georgi have been identified on-line without time-consuming isolation. The HPLC–ESI-MSn method for analyzing constituents in the Scutellaria baicalensis Georgi has been established.

Studies on the flavones using liquid chromatography–electrospray ionization tandem mass spectrometry

Fragmentation pathways of nine flavone compounds have been studied by using electrospray ionization multi-stage tandem mass spectrometry (ESI-MS n ). Analyzing the product ion spectra of flavonoids and aglycones, we observed some diagnostic neutral losses, such as CH 3, H 2O, residue of glucose and gluconic acid, which are very useful for the identification of the functional groups in the structures. Furthermore, specific retro Diels-Alder (RDA) fragments for flavones with different hydroxyl substitution have also been discussed. The information is helpful for the rapid identification of the location site of hydroxyl substitution on flavones. Fragmentation pathways of C-glycosidic flavonoid have also been discussed using ESI-MS n , demonstrating ions [ M H-60] −, [ M H-90] −, [ M H-120] − are characteristic ions of C-glycosidic flavonoid. According to the fragmentation mechanism of mass spectrometry and HPLC–MS data, the structures of seven flavones in Scutellaria baicalensis Georgi have been identified on-line without time-consuming isolation. The HPLC–ESI-MS n method for analyzing constituents in the Scutellaria baicalensis Georgi has been established.

Novel benzyl rearrangements in electrospray ionization multistage tandem mass spectra of benzyl 2',3'- didehydro-2',3'-dideoxythymidin-5'-yl H-phosphonate.

Several alkyl 2',3'-didehydro-2',3'-dideoxythymidin-5'-yl H-phosphonates were synthesized and analyzed by electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). Two kinds of novel benzyl rearrangement reactions were observed in ESI - MS(2) of [M + H](+), [M + Na](+) and [M + K](+) of benzyl 2',3'-didehydro-2',3'-dideoxythymidin-5' yl H-phosphonate. Results from tandem mass spectrometry, high-resolution mass spectrometry and control experiments showed that the benzyl migration could undergo a four-membered cyclic rearrangement reaction, and benzyl was essential in the process.

On-line identification of phenanthroindolizidine alkaloids in a crude extract from Tylophora atrofolliculata by liquid chromatography combined with tandem mass spectrometry.

Electrospray ionization multi-stage tandem mass spectrometry (ESI-MS(n)) and liquid chromatography coupled with sequential mass spectrometry (LC/MS(n)) were applied to identify trace-level phenanthroindolizidine alkaloids in crude extracts from Tylophora atrofolliculata. Based on the relationship between the characteristic fragmentation reactions and the structural features of related compounds of known structure from this plant, the bioactive crude extract was analyzed in detail by positive and negative ion ESI-MS(n), LC/UV-MS and LC/MS(n) techniques. A total of nine constituents in the crude extract were identified rapidly, including several isomers; seven of these constituents are new and two are known compounds. The structures of four of these constituents were subsequently confirmed by nuclear magnetic resonance (NMR) and accurate mass measurements using high-resolution fast-atom bombardment mass spectrometry (FAB-HRMS).

Structural analysis of saponins from medicinal herbs using electrospray ionization tandem mass spectrometry

The underivatized saponins from Tribulus terrestris and Panax ginseng have been investigated by electrospray ionization multi-stage tandem mass spectrometry (ESI-MS n). In ESI-MS spectra, a predominant [M + Na] + ion in positive mode and [M − H] − ion in negative mode were observed for molecular mass information. Multi-stage tandem mass spectrometry of the molecular ions was used for detailed structural analysis. Fragment ions from glycoside cleavage can provide information on the mass of aglycone and the primary sequence and branching of oligosaccharide chains in terms of classes of monosaccharides. Fragment ions from cross-ring cleavages of sugar residues can give some information about the linkages between sugar residues. It was found that different alkali metal-cationized adducts with saponins have different degrees of fragmentation, which may originate from the different affinity of a saponin with each alkali metal in the gas phase. ESI-MS n has been proven to be an effective tool for rapid determination of native saponins in extract mixtures, thus avoiding tedious derivatization and separation steps.

Rapid analysis of a triterpenoid saponin mixture from plant extracts by electrospray ionization multi-stage tandem mass spectrometry (ESI-MSI).

Rapid analysis of a triterpenoid saponin mixture from plant extracts by electrospray ionization multi-stage tandem mass spectrometry (ESI-MSI).

Rapid identification of saponins in plant extracts by electrospray ionization multi-stage tandem mass spectrometry and liquid chromatography/tandem mass spectrometry.

Electrospray ionization multi-stage tandem mass spectrometry (ESI-MS(n)) and liquid chromatography coupled with on-line mass spectrometry (LC/MS/MS) were applied to characterize saponins in crude extracts from Panax ginseng. The MS(n) data of the [M - H](-) ions of saponins can provide structural information on the sugar sequences of the saccharide chains and on the sapogins of saponins. By ESI-MS(n), non-isomeric saponins and isomeric saponins with different aglycones can be determined rapidly in plant extracts. LC/MS/MS is a good complementary analytical tool for determination of isomeric saponins. These approaches constitute powerful analytical tools for rapid screening and structural assignment of saponins in plant extracts.