Collision-Induced Dissociation Analysis of Brevianamide A and C in Electrospray Ionization Mass Spectrometry

Ana Lígia L De Oliveira,Norberto P Lopes,Hosana M Debonsi,Ricardo Vessecchi

doi:10.5935/0103-5053.20150029

Ana Lígia L De Oliveira, Norberto P Lopes + Show 2 more

Open Access

https://doi.org/10.5935/0103-5053.20150029

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Abstract

Brevianamides A and C are isomeric cyclic peptides with several reported biological activities, isolated from diverse microorganisms. Currently, there has been no previous investigation of brevianamide fragmentation utilizing electrospray ionization mass spectrometry (ESI-MS). In this work experiments were carried out in the positive mode using two different spectrometers (low and high resolution) with an ESI source. Computational chemistry studies helped identify the protonation sites based upon atomic charges, proton affinities and molecular orbitals, computed using the B3LYP/6-31++G (d,p) model. The data suggests that the presence of the allylic position of the lactamic N in brevianamides C governs its fragmentation pathways. Distinguishing between brevianamides A and C using positive ion electrospray tandem mass spectrometry (ESI(+)MS/MS) is made possible by the spectral difference of each isomer and offers an alternative to other spectroscopic techniques.

Highlights

Diketopiperazines are cyclic natural dipeptides that have been isolated from microorganisms, sponges, sea stars, tunicates and red algae.[1]
Analysis of two brevianamides isomers A and C showed the influence of the presence of a double bound between carbons 2-8 in brevianamide C instead of the additional ring contained in brevianamide A
The spectra acquired via the QTOF and ion trap spectrometers displayed the diagnostic m/z 338 fragment-ion (CO elimination)

Summary

Introduction

Diketopiperazines are cyclic natural dipeptides that have been isolated from microorganisms, sponges, sea stars, tunicates (ascidians) and red algae.[1] These compounds show significant pharmacological effects and have been classified as promising leads in drug discovery. The authors concluded that the chemical simplicity of these compounds, their rigid structure, chiral nature and the possibility to contain a large variety of side chains enable diketopiperazines to act on several different receptors, giving them a range of medicinal applications.[2] Brevianamides are a class of diketopiperazines that normally have an additional bicyclo[2.2.2]diazoctane ring system.[3] Their biological activity has inspired several researchers to investigate their biosynthesis and pharmacological benefits, as well as new synthetic routes.[4,5,6]

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