Narcissus and Daffodil

170 J. Bastida and F. Viladomat
Figure 6.11 Proposed biosynthetic pathways to haemanthamine (49) and montanine (85).
tion of the precursors should be norbelladine (83) --> N-methylnorbelladine -->
N,O-dimethylnorbelladine (90) to give finally galanthamine (69) (Barton et al.,
1963), the conversion of 91 to narwedine (76) either being not reversible or, if so,
enzymically controlled (Fuganti, 1969). The precursor N,O-dimethylnorbelladine
(90) was first isolated in 1988 from Pancratium maritimum (Vázquez-Tato et al.,
1988), a species that also contains galanthamine (69) (Figure 6.12a).
Chlidanthine (92), by analogy with the known conversion of codeine to morphine,
might be expected to arise from galanthamine (69) by O-demethylation. This was
shown to be true when both galanthamine (69) and narwedine (76), with tritium
labels, were incorporated into chlidanthine (92) (Bhandarkar and Kirby, 1970).
However, the most recent study seems to contradict the evidence set forth here.
Experiments carried out with application of 13 C-labelled O-methylnorbelladine
(80) to organs of field grown Leucojum aestivum have shown that the biosynthesis of
galanthamine (69) involves the phenol oxidative coupling of O-methylnorbelladine
(80) to a postulated dienone which undergoes spontaneous closure of the ether
bridge to yield N-demethylnarwedine (93), giving norgalanthamine (72) after
stereoselective reduction. Furthermore, it was shown that norgalanthamine (72) is