Narcissus and Daffodil

166 J. Bastida and F. Viladomat
Figure 6.6 Biosynthesis of lycorine (1) with inversion of the configuration.
Figure 6.7 Conversion of galanthine (7) to narcissidine (16) via epoxide (86).
tritiated lycorine (1) by Narcissus × incomparabilis cv. Deanna Durbin, which not only
demonstrates the previously mentioned conversion but also indicates that the C-2
hydroxyl group of lycorine (1) is derived by allylic oxidation of either norpluviine
(12) or caranine (10) (Battersby et al., 1964).
Regarding the conversion of [2β- 3 H, 8-OMe- 14 C]pluviine (11) into galanthine
(7), in Narcissus pseudonarcissus cv. King Alfred, the retention of 79% of the tritium
label confirms that hydroxylation of C-2 may occur with inversion of configuration
(Harken et al., 1976).
It was considered (Fuganti et al., 1974a) that another analogous epoxide 86
could give narcissidine (16) in the way shown by loss of the pro-S hydrogen from
C-11, galanthine (7) being a suitable substrate for epoxidation. Labelled [α- 14 C,
β- 3 H]-O-methylnorbelladine (80), when fed to Narcissus x incomparabilis cv. Sempre
Avanti, afforded galanthine (7) (98% of tritium retention) and narcissidine (16)
(46% tritium retention). Loss of hydrogen from C-11 of galanthine (7) was therefore
stereospecific. In this decade, Kihara et al. (1992) have isolated a new alkaloid,
incartine (86), from flowers of Lycoris incarnata, which could be considered to be
the biosynthetic intermediate of this pathway (Figure 6.7).
The biological conversion of protocatechuic aldehyde into lycorenine (31),
which proceeds via O-methylnorbelladine (80) and norpluviine (12), first involves
a reduction of the aldehyde carbonyl, and afterwards, in the generation of lycorenine
(31), oxidation of this same carbon atom. The absolute stereochemistry of
these processes has been elucidated in subsequent experiments (Fuganti and
Mazza, 1973), and the results show that hydrogen addition and removal take place
on the re-face of the molecules concerned (Hanson, 1966), the hydrogen initially
introduced being the one later removed (Fuganti and Mazza, 1971a). It is noteworthy
that norpluviine (12), unlike pluviine (11), is converted in Narcissus pseudonarcissus
cv. King Alfred primarily to alkaloids of the homolycorine type. Benzylic oxidation