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

Author(s)

Neto, Fausto Carnevale ; Andreo, Marcio Adriano ; Raftery, Daniel ; Callegari Lopes, Joao Luis ; Lopes, Norberto Peporine ; Castro-Gamboa, Ian ; de Noronha Sales Maia, Beatriz Helena Lameiro ; Costa, Emmanoel Vilaca ; Vessecchi, Ricardo

• Document type: Journal article
• Source: RAPID COMMUNICATIONS IN MASS SPECTROMETRY; v. 34, p. 11-pg., 2019-10-29.

Abstract

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)-O-center dot elimination instead of the expected neutral loss of the heterocyclic amino group, pointing to the [M - 15 + H](center dot+) 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. (AU)

• FAPESP's process: 09/08281-3 - Gas-phase reactivity of quinonoid compounds lapachol derivatives by electrospray ionization: Synergism between computational and experimental methods
• Grantee: Ricardo Vessecchi Lourenço
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 14/50265-3 - Distribution and metabolism of natural and synthetic xenobiotics: from the comprehension of reactional process to tissue imaging generation
• Grantee: Norberto Peporine Lopes
• Support Opportunities: BIOTA-FAPESP Program - Thematic Grants
• FAPESP's process: 14/12343-2 - Method development and prospection studies of marine biological resources with citotoxic potential based on systems biology
• Grantee: Fausto Carnevale Neto
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 14/23604-1 - Computational chemistry: a tool to studies of mass spectrometry, reactivity and fragmentation/reaction mechanisms of organic compounds
• Grantee: Ricardo Vessecchi Lourenço
• Support Opportunities: Regular Research Grants
• FAPESP's process: 10/07564-9 - Study of Chrysobalanaceae species with cytotoxic activities: Metabolomic analysis for the understanding of sinergistic associations and their micromolecular complexity
• Grantee: Fausto Carnevale Neto
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 03/02176-7 - Conservation and sustainable use of the diversity from Cerrado and Atlantic Forest: chemical diversity and prospecting for potential drugs - phase II
• Grantee: Vanderlan da Silva Bolzani
• Support Opportunities: BIOTA-FAPESP Program - Thematic Grants