Fragmentation pathways of protonated coumarin by ESI-QE-Orbitrap-MS/MS coupled with DFT calculations

Coumarin is one of the basic structures of naturally oxygen heterocyclic compound, which was investigated in this paper for its gas-phase fragmentation behaviors using electrospray quadrupole extractive orbitrap mass spectrometry in the positive mode. The possible fragmentation pathways were proposed based on electrospray ionization (ESI)- mass spectrometry (MS)/MS data and theory calculation. The elimination of two CO and CO₂ was observed for protonated coumarin, which was followed by the formation of a stabilized seven-, six-, and five-membered ring carbocation by loss of C2H2. The possible protonation sites occurred at Oxygen 11 atom of coumarin were the main fragmentation pathways. The relative abundance of characteristic fragment ions and the energy-resolved breakdown curves were used to confirm the cleavage mechanism of protonated coumarin. The methodology and results of present work would contribute to the chemical structure identification of other coumarins.