Fragmentation studies of pentacoordinated bisaminoacylspirophosphoranes by negative electrospray ionization mass spectrometry

Fragmentation pathways of a series of pentacoordinated bisaminoacylspirophosphoranes were elucidated by electrospray ionization multistage mass spectrometry (ESI-MS(n)) in negative mode. The deprotonated ions of pentacoordinated bisaminoacylspirophosphoranes tend to eliminate a corresponding amino acid to form base peak. The hydrogen/deuterium exchange experiment, the high-resolution mass spectrometry, (13)C stable isotope labeling experiment and theoretical calculations were used to rationalize the proposed fragmentation pathways and to verify the differences between the fragmentation pathways. The results indicate that the negative molecular ions of pentacoordinated bisaminoacylspirophosphoranes dissociate through its open-chain tricoordinated tautomers. The relative Gibbs free energies (ΔG) of the product ions and proposed fragmentation pathways were estimated using the B3LYP/6-31 + + G(d, p) model. The results have some potential applications in the identification structures of similar spirophosphorane compounds by ESI-MS(n).