FRAGMENTATION OF SUBSTITUTED PYRIMIDO[6,1-A]ISOQUINOLIN-2-ONES UNDER ELECTRON IONIZATION

The mass spectral fragmentations of eight substituted pyrimido[6,1-a]i soquinolin-2-ones and four pyrimido[6,1-a]isoquinoline-2,4-diones unde r electron ionization were examined by metastable ion analysis, a coll ision-induced dissociation technique and exact mass measurements, The major fragmentation pathways began as radical site-initiated cleavage, and ionization of the nitrogen atom in the isoquinoline ring seemed t o prevail, Only the isoquinolinediones gave fragments resulting from i onization of the phenyl ring. Substituents on N3 and C4 had larger eff ects on the peak intensities than substituents on C6., The major fragm entation pathway was different from that for the related oxazino[4,3-a ]isoquinolines studied earlier. (C) 1997 John Wiley & Sons, Ltd.