Gas-phase fragmentation study of a novel series of synthetic 2-oxo-2H-benzopyrano[2,3-d]pyrimidine derivatives using electrospray ionization tandem mass spectroscopy measured with a quadrupole orthogonal time-of-flight hybrid instrument.

The fragmentation patterns of a series of six novel synthesized benzopyranopyrimidine derivatives 1-6, possessing the same 2-oxo-2H-benzopyrano[2,3-d]pyrimidine backbone structure, were investigated by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) techniques using a quadrupole orthogonal time-of-flight (QqToF)-hybrid instrument. The series of six pure benzopyranopyrimidine compounds contained three constitutional isobaric isomers (compounds 4-6). A simple methodology, based on the use of ESI (positive ion mode) and increasing the declustering potential in the atmospheric pressure/vacuum interface resulting in collision-induced dissociation (CID), was used to enhance the formation of the product ions. In general, the novel synthetic benzopyranopyrimidine derivatives 1-6 afforded exact accurate masses for the protonated molecules. This led to the confirmation of both molecular masses and chemical structures of the studied compounds. The breakdown routes of the protonated molecules were rationalized by conducting low-energy CID-MS/MS analyses. It was shown that the MS/MS fragmentation routes for the protonated molecules 1 and 2 were similar, and that the MS/MS fragmentations of the constitutional isobaric protonated molecules 5 and 6 were identical. It was also shown that the gas-phase CID fragmentations of 5 and 6 were different from that of their constitutional isomer 4. Finally, the ESI-MS and CID-MS/MS analyses of the protonated molecules that were obtained from the monodeuterated benzopyranopyrimidine derivatives 1-6 confirmed the values obtained for the exact masses, the precise structural assignments of all product ions and all the pathways described in the proposed CID fragmentations.