Mass-spectrometric studies on alkylated 6-thiopurines

6-Thiopurine and its N- or C-alkyl derivatives all form an [M – 1]-ion upon fragmentation. In the 7-alkyl derivatives, this ion represents the major component of the spectrum. This is ascribed to formation of a five-membered thiazoline-like ring. Similar ring formation stabilises the [M – 1]-ion in the 7-methyl derivatives of hypoxanthine, adenine and 6-selenopurine.