Synthesis and mass spectrometric behavior of some new nucleosides as potential anti-HIV agents.

The electron-impact (EI) mass spectrometric behaviour of a series of 8-aza-purines derivatized with hydroxymethylcyclopentane and exhibiting cis-trans isomerization in the cyclopentane ring has been studied in detail with the aid of metastable-ion data. Specific fragmentation processes, present in both EI and mass analysed ion kinetic energy spectra of molecular species, allow characterization of the different pairs of stereoisomers. Contrary to what is observed in the case of purine analogs, the presence of a nitrogen atom in position 8 strongly inhibits fragmentation processes related to the heterocycle.