Electrospray ionization tandem mass spectrometry of monoketone curcuminoids

Author(s)

Vieira, Tatiana M. ; Orenha, Renato P. ; Crevelin, Eduardo J. ; Furtado, Saulo S. P. ; Vessecchi, Ricardo ; Parreira, Renato L. T. ; Crotti, Antonio E. M.

• Document type: Journal article
• Source: RAPID COMMUNICATIONS IN MASS SPECTROMETRY; v. 34, p. 17-pg., 2020-02-11.

Abstract

Rationale Although monoketone curcuminoids (MKCs) have been largely investigated due to their biological activities, data on the gas-phase fragmentation reactions of protonated MKCs under collision-induced dissociation (CID) conditions are still scarce. Here, we combined electrospray ionization tandem mass spectrometry (ESI-MS/MS) data, multiple-stage mass spectrometry (MSn), deuterium exchange experiments, accurate-mass data, and thermochemical data estimated by computational chemistry to elucidate and to rationalize the fragmentation pathways of eleven synthetic MKCs. Methods The MKCs were synthesized by Claisen-Schmidt condensation under basic (1-9) or acidic (10-11) conditions. ESI-CID-MS/MS analyses and deuterium-exchange experiments were carried out on a triple quadrupole mass spectrometer. MSn analyses on an ion trap mass spectrometer helped to elucidate the fragmentation pathways. Accurate-mass data and thermochemical data, obtained at the B3LYP/6-31+G(d,p) level of theory, were used to support the ion structures. Results The most intense product ions were the benzyl ions ([C7H2R1R2R3R4R5](+)) and the acylium ions ([M + H - C8H3R1R2R3R4R5](+)), which originated directly from the precursor ion as a result of two competitive hydrogen rearrangements. Product ions [M + H - H2O](+) and [M + H - C6HR1R2R3R4R5](+), which are formed after Nazarov cyclization, were also common to all the analyzed compounds. In addition, center dot Br and center dot Cl eliminations were diagnostic for the presence of these halogen atoms at the aromatic ring, whereas center dot CH3 eliminations were useful to identify the methyl and methoxy groups attached to this same ring. Nazarov cyclization in the gas phase occurred for all the investigated MKCs and did not depend on the presence of the hydroxyl group at the aromatic ring. However, the presence and the position of a hydroxyl group at the aromatic rings played a key role in the Nazarov cyclization mechanism. Conclusions Our results reinforce some aspects of the fragmentation pathways previously published for 1,5-bis-(2-methoxyphenyl)-1,4-pentadien-3-one and 1,5-bis-(2-hydroxyphenyl)-1,4-pentadien-3-one. The alternative fragmentation mechanism proposed herein can explain the fragmentation of a wider diversity of monoketone curcuminoids. (AU)

• FAPESP's process: 11/07623-8 - The use of quantum-mechanical methods to study the bonds and chemical interactions in self-organizing systems with applications in catalysis, medicinal chemistry, electrochromism, energy storage and conversion
• Grantee: Renato Luis Tame Parreira
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 17/24856-2 - The Mechanism of the Substitution Reaction of the Ligand Nitrosyl by Aqua in Ruthenium Coordination Compounds
• Grantee: Renato Pereira Orenha
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 16/19272-9 - Evaluation of the antimicrobial activity of curcuminoids and study of their fragmentation reactions in the gas-phase by tandem mass spectrometry
• Grantee: Tatiana Manzini Vieira
• Support Opportunities: Scholarships in Brazil - Master