Narcissus and Daffodil

182 J. Bastida and F. Viladomat
Figure 6.15 Mass fragmentation pattern of haemanthamine (49).
The presence of a hydroxyl group on C-11 is responsible for dramatic changes
in the fragmentation pattern (Figure 6.15), and it is profoundly influenced by
the stereochemistry. There are three fundamental patterns of fragmentation:
1 Loss of CH 3 OH: it is more favourable when the two-carbon bridge and the
substituent on C-3 are on the same side of the molecule.
2 Loss of C 2 H 6 N: the relative significance of the loss of this neutral nitrogen
moiety is governed by the ease with which the methanol is eliminated.
3 Loss of CHO: A peak at m/z [M-29] due to the loss of an aldehyde radical is
present in all compounds of this type.
Tazettine type
Minor changes in stereochemistry are sufficient to cause appreciable differences in
the stereoisomers in these kind of structures. Thus, in the MS of tazettine (58),
with a β configuration of the methoxyl group at C-3, the dominant ion occurs at
m/z [M-84], following a C-ring fragmentation by a retro Diels-Alder process.
In contrast, the mass spectrum of criwelline (59), which differs only in the
configuration of the mentioned methoxyl group, contains a peak of low abundance
at m/z [M-84] (Figure 6.16). Ions occur in both steroisomers due to the
successive loss of a methyl radical and water from the molecular ion (Duffield
et al., 1965).