Fragmentation study of noscapine derivatives under electrospray conditions

Simultaneous Detection Method of 11 Respiratory Drug Substances Including Theobromine, Oxymetazoline, etc. in Adulterated Dietary Supplements Using Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry and Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry Analysis

Recently, the demand for respiratory disease-related products has surged due to the influence of coronavirus disease 2019, prompting warnings about illegal dietary supplements containing unauthorized substances. Additionally, adulterated dietary supplements are continuously detected in open markets, posing significant public health safety problem. In this study, we developed and validated an analytical method for 11 respiratory drug substances using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) and proposed optimal conditions for LC-quadrupole time-of-flight MS (LC-QTOF-MS) to determine the fragmentation patterns of each substance. This method underwent thorough validation considering specificity, linearity, limits of detection and quantification, accuracy, precision, matrix effect, stability, etc. All results met international guidelines. These validated methods were applied to 52 dietary supplements advertised for treating respiratory diseases and enhancing respiratory function, among which one sample was found to contain 313.7 mg/g of theobromine. This determination was made by comparing the product ion ratios with the standards and subsequent quantification. To re-confirm the detected substances, their fragmentation patterns were compared with those of the standards using LC-QTOF-MS. In conclusion, the mass-based information, coupled with the LC-ESI-MS/MS method development, can be successfully applied to rapidly identify 11 respiratory drug substances in illegal dietary supplements used for respiratory disease treatment. The developed simultaneous detection method contributes to public health and safety improvements.

Investigation of fragmentation behaviours of isoquinoline alkaloids by mass spectrometry combined with computational chemistry

Isoquinoline alkaloids, which are one of the most important types of alkaloids, are extensively distributed in herbal medicines. However, systematic and comprehensive investigations of the fragmentation behaviours of isoquinoline alkaloids have rarely been reported. Therefore, the goal of the present study is to simultaneously investigate the collision-induced dissociation patterns and the corresponding mechanism of isoquinoline alkaloids by mass spectrometry (MS) combined with computations. Nineteen types of isoquinoline alkaloids (66 compounds) were used as references to identify the characteristic fragmentation behaviours by quadrupole time-of-flight mass spectrometry (Q-TOF/MS) in positive electrospray ionization (ESI) mode. These types of isoquinoline alkaloids were divided into three categories primarily by the characteristic [M-NHR₁R₂]⁺ (R₁ and R₂ represent the substituent groups of the N-atom) fragment ions. High- and low-abundance [M-NHR₁R₂]⁺ ions were observed respectively for type I (1–13) and type II (14–29) alkaloids, respectively; however, the characteristic fragments were not detected for type III alkaloids (30–66) because of the existence of a p-π conjugated system. Each type of alkaloid was further classified by its characteristic fragmentation patterns and fragment ions. In addition, isoquinoline alkaloid with vicinal methoxy and hydroxy, vicinal methoxy, methylenedioxy, methoxy, and quaternary N-methyl groups could form the characteristic fragments by the loss of CH₃OH, CH₄, CH₂O or CO, CH₃ and CO, and CH₃ moieties, respectively. The mechanisms of some interesting fragmentation behaviours, such as the formation of [M-NH₃]⁺ and [M-CH₃]⁺ fragment ions, were further demonstrated by computational chemistry. These characteristic fragmentation behaviours and fragment ions of isoquinoline alkaloids provide a solid foundation for the rapid and high-efficiency structural elucidation of similar metabolites in plant-derived medicines.

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.