Studies on Pyrazolo[3, 4-d]pryimidine Derivatives.VII. : Mass Spectra of Pyrazolo[3, 4-d]pyrimidine 5-Oxides

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Masspectra(MS)of 1-methyl-(I), 4-substituted 1-phenyl-1 H-pyrazolo[3, 4-d]pyrimidine 5-oxides(II)and 1, 5-dihydro1-methylpyrazolo[3, 4-d]pyrimidine-4-one(III)were examined. The possible principle fragmentation of I and II is summarized by the four dissociation paths, that is, the loss of oxygen atom from the molecular ion(M+), the loss of carbon monoxide from the rearranged molecular ion b, the successive losses of hydrogen radical and carbon monoxide from M+, and also the successive losses of hydrogen radical and oxygen atom from M1, ashown in path 1 to 4 in Scheme 1. In MS of II b, the isopropyl group at the 4-position easily dissociates, so that IIb does not undergo the skeletal rearrangement involving path 2 and 3. The one step loss of hydroxy radical from M+ and the loss of nitrogen monoxide from M+are difficult to find in MS of I and II. The pressure dependency is widely observed for many of the fragment ions, especially the ions concerned with path 1 are typical, of the pressure dependency.
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