Characterization of aporphine alkaloids by electrospray ionization tandem mass spectrometry and density functional theory calculations

Rationale Aporphine alkaloids represent a large group of isoquinoline natural products with important roles in biological and biomedical areas. Their characterization by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) can contribute to their rapid identification in complex biological ma...

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Published in:Rapid communications in mass spectrometry 2020-09, Vol.34 (S3), p.e8533-n/a
Main Authors: Carnevale Neto, Fausto, Andréo, Márcio Adriano, Raftery, Daniel, Lopes, João Luis Callegari, Lopes, Norberto Peporine, Castro‐Gamboa, Ian, Lameiro de Noronha Sales Maia, Beatriz Helena, Costa, Emmanoel Vilaça, Vessecchi, Ricardo
Format: Article
Language:English
Subjects:
Alkaloids
Annotations
Density functional theory
Diagnostic systems
Electrospraying
Fragmentation
Identification methods
Ionization
Ions
Mass spectrometry
Natural products
Scientific imaging
Spectroscopy
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Summary:Rationale Aporphine alkaloids represent a large group of isoquinoline natural products with important roles in biological and biomedical areas. Their characterization by electrospray ionization tandem mass spectrometry (ESI‐MS/MS) can contribute to their rapid identification in complex biological matrices. Methods We report the fragmentation of protonated 7,7‐dimethylaporphine alkaloids by ESI‐MS/MS, and the putative annotation of aporphine alkaloids in plant extracts. We used low‐ and high‐resolution MS/MS analyses to rationalize the fragmentation pathways, and employed the B3LYP/6‐31 + G(d,p) density functional theory (DFT) model to provide thermochemical parameters and to obtain the reactive sites. Results DFT calculations of a set of 7,7‐dimethylaporphine alkaloids suggested the heterocyclic amino group as the most basic site due to the proton affinity of the nitrogen atom. Collision‐induced dissociation experiments promoted •OCH3 elimination instead of the expected neutral loss of the heterocyclic amino group, pointing to the [M − 15 + H]•+ ion as the diagnostic fragment for 7,7‐dimethylaporphine alkaloids. The analysis of plant extracts led to the annotation of 25 aporphine alkaloids. Their fragmentation initiated with the loss of the amino group followed by formation of a cyclic carbocation. Further reactions derived from consecutive charge‐remote and/or charge‐induced fragmentations of the substituents attached to the aromatic system. The mechanisms were re‐examined based on plausible gas‐phase ion chemistry reactions. Conclusions Taken together, the diagnostic product ions and the series of radical and neutral eliminations provided information about the location of methylenedioxy, aromatic methoxy, and vicinal methoxy and hydroxy groups in aporphine alkaloids, assisting their characterization via MS/MS.
ISSN:0951-4198
1097-0231
DOI:10.1002/rcm.8533