STRUCTURAL STUDIES OF POLYHYDROXYBIS(TETRAHYDROFURAN)ACETOGENINS FROMANNONA-SQUAMOSA USING THE COMBINATION OF CHEMICAL DERIVATIZATION AND PRECURSOR-ION SCANNING MASS-SPECTROMETRY

The structure of squamocin polyhydroxybis(tetrahydrofuran)acetogenin f rom Annona squamosa L., was characterized by a combination of the chem ical derivatization and precursor-ion scanning mass spectrometry. The lactone part of squamocin was modified with NN-dimethylethylenediamine in the vapour phase to afford a strong positive charge at one end of the skeleton. The derivative was ionized by fast atom bombardment (FAB ), and the production spectrum from [M + H]+ and the precursor ion spe ctrum from the m/z 72 ion [CH2-CHN+H(CH3)2] generated by low-energy co llision were acquired, The structure of the derivative could be charac terized by the precursor-ion spectrum from the m/z 72 ion, but little structural information could be obtained from the production spectrum from [M + H]+ of the derivative. By the attachment of a tertiary amino group to one end of the skeleton, charge-remote fragmentation was fac ilitated and abundant and unique fragment ions were observed im the pr ecursor-ion spectrum. Structural characterization of six other isolate d compounds was also carried out, and two novel compounds were found b y this technique. A similar derivatization was applied in the peptide leu-enkephalin, and full sequencing from the C-terminus using precurso r-ion scanning from m/z 72 could be achieved.