MASS-SPECTROMETRIC STUDY OF THE AMIPURIMYCIN HEXOPYRANOSIDIC SUGAR MOIETY

Amipurimycin is a natural nucleoside that displays a remarkable activi ty in vitro and in vivo against Pyricularia oryzae, which is responsib le for the rice blast disease. Six important precursors for the synthe sis of the Amipurimycin sugar moiety were prepared. In order to obtain structural information a mass spectrometric study of these compounds was performed using liquid secondary ion mass spectrometry (LSIMS) wit h high-energy collision-induced dissociation (CID) experiments on a fo ur-sector instrument. Elimination of methanol is the preferential frag mentation path for five of the six protonated molecules, indicating th at protonation plays an important role in the process, whilst for the other protonated molecule loss of water is the main fragmentation. Exa mination of the [M + Li](+) precursor ion spectra shows that loss of m ethanol does not occur in three of them, but in the other three gives rise to fairly abundant ions, indicating that in this case methanol el imination implies intramolecular hydrogen transfer, the resulting ion having a very stable structure.