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The electron impact m a s spectra of N-(lH-hxo-4pyrimidinyl) amino acids are discussed. It was established that thermal elimination of water took place prior to mass fragmentation of all thee compounds with the formation of bicyclic structures. The fragmentation of bicyclic ions led to lH-hxo-pyrimidinyl species.

Electron impact (El) mass spectra of fourteen Qamino-substituted 1,2aihydro-l-methylpyrimidibZoaes are reported. The EI-induced decomposition of their molecular ions is significantly dependent on the chemical nature of the substitwnts. The routes of mass decomposition established suggest the presence of the tautomeric forms in the gas phase of some investigated compounds.

The electron-impact-induced mass fragmentations of methyl esters of N-( lH-2-ox04pyrimidinyl)amino acids are reported. The loss of a 'COOCH, radical and the elimination of a methanol molecule were observed and possible mechanisms of these processes are proposed. The loss of a 'COOH radical and elimination of water were established, which suggests the rearrangement of the investigated esters into isomeric N-Qpyrimidinylamino acids.

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