Narcissus and Daffodil

168 J. Bastida and F. Viladomat
Figure 6.9 Alkaloids proceeding from a para-para′ coupling.
this plant converts haemanthamine (49) to haemanthidine/epihaemanthidine (51/52)
and subsequently to pretazettine (60) in an essentially irreversible manner (Fales
and Wildman, 1964). This transformation was considered to proceed through 88a
or the related alkoxide anion, although this intermediate 88a and its rotational
equivalent 88b have never been detected by spectral methods (Wildman and
Bailey, 1969) (Figure 6.10).
It has also been proved that the alkaloid narciclasine (63) proceeds from the
pathway of the biosynthesis of crinine and haemanthamine type alkaloids and not
through norpluviine (12) and lycorine (1) derivatives. In fact, in view of its structural
affinity to both haemanthamine (49) and lycorine (1), narciclasine (63) could be
derived by either pathway. When O-methylnorbelladine (80), labelled in the methoxy
carbon and in both protons of position 3 and 5 of the tyramine aromatic ring, was
administered to narcissus plants, all four alkaloids incorporated activity. The isotopic
ratio [ 3 H: 14 C] for norpluviine (12) and lycorine (1) was, as expected, 50% that of the
precursor, because of its ortho-para′ coupling. On the contrary, in haemanthamine
(49) the ratio was unchanged. These results prove that the methoxy group of (80)
is completely retained in the alkaloids mentioned, providing a satisfactory internal
standard, and also the degree of tritium retention is a reliable guide to the direction
of phenol coupling. Narciclasine (63) showed an isotopic ratio (75%) higher than
that of lycorine or norpluviine (12) though lower than that of hemanthamine (49).
However, the fact that more than 50% of tritium is retained suggests that O-methylnorbelladine
(80) is incorporated into narciclasine (63) via para-para′ phenol
oxidative coupling.
O-methylnorbelladine (80) and vittatine (39) are implicated as intermediates in
the biosynthesis of narciclasine (63) (Fuganti et al., 1971; Fuganti and Mazza,