Structure-fragmentation study of pentacyclic triterpenoids using electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOFMS/MS).

Rationale: Pentacyclic triterpenoids are secondary plant metabolites widespread in fruit peel, leaves, and stem bark. Due to their important biological activities, these compounds are widely screened using advance analytical techniques like electrospray ionization (ESI) mass spectrometry. Over the past few decades, the practice of ESI has been refined into a versatile ionization technique for a wide variety of analytes differing in their chemical makeup, size, complexity, and bimolecular stability.

Methods: The structure-fragmentation relationships (SFRs) of 16 pentacyclic triterpenoids were studied using a positive ion ESI quadrupole time-of-flight mass spectrometry (ESI-QqTOFMS/MS) hybrid instrument.

Results: ESI-QqTOFMS (positive ion mode) showed the presence of the protonated molecules [M + H] of most of analyzed compounds. Low-energy collision-induced dissociation MS/MS analysis of these molecules indicated multiple losses of water molecules and the loss of the formic acid moiety [M + H - HCOOH] and other substituents as the predominant pathway for further fragmentation. Key product ions were identified which resulted from the retro-Diels-Alder cleavage of the ring system. SFRs of all the compounds analyzed were also developed.

Conclusions: We developed a fragmentation pattern of pentacyclic triterpenoids using the ESI-QqTOFMS/MS technique. It was concluded that the formation of key product ions and loss of characteristic neutrals can give detailed insight into structural information about the basic structure and attached substituents.