Narcissus and Daffodil

6 Alkaloids of Narcissus
Jaume Bastida and Francesc Viladomat
INTRODUCTION
Since the isolation of the first Amaryllidaceae alkaloid, lycorine (1), from Narcissus
pseudonarcissus by Gerrad at the end of the last century, more than 200 species and
varieties belonging to this plant family have been examined for alkaloids.
Although this group of alkaloids has been of minor pharmaceutical importance
until recently, there has been an increased interest due to the possible applications
of galanthamine (69), an alkaloid isolated exclusively from species of this family.
There are several reviews of Amaryllidaceae alkaloids (Ghosal et al., 1985b; Martin,
1987) and, likewise, this topic is regularly reviewed by the journal Natural Products
Reports of The Royal Society of Chemistry (Lewis, 1998, and previous years). This
chapter covers phytochemical studies on Narcissus alkaloids up to March 1999.
There has been considerable taxonomical controversy over which genera belong
to the Amaryllidaceae. The revisions of Dahlgren’s group (Dahlgren, 1980; Dahlgren
et al., 1985) have contributed to clarifying this aspect. On the other hand, one
of the best tools for the classification of several genera and species of this family
has been the type of alkaloids that are found exclusively in Amaryllidaceae.
Furthermore, it is unusual to find other types of alkaloids in Amaryllidaceae, but if
present, they are always accompanied by typical Amaryllidaceae alkaloids. Up to
now, only three alkaloids isolated from this family do not belong to this specific
type, but to the mesembrane (Sceletium) type generally found in the Aizoaceae
family (Jeffs, 1981), and for this reason the Amaryllidaceae alkaloids have a high
chemotaxonomical value. One of these compounds, mesembrenone (82), was
isolated from Narcissus pallidulus (Bastida et al., 1989) (Figure 6.1).
The general characteristics of the Amaryllidaceae alkaloids can be summarised
as follows:
1 A fundamental ring system composed of a C 6 –C 1 and an N–C 2 –C 6 building
block, derived from L-phenylalanine and L-tyrosine, respectively.
2 They are moderately weak bases (pKa values of 6–9).
3 Each alkaloid contains only one nitrogen atom which is secondary, tertiary or
even quaternary, and the carbon content varies from 16 to 20 atoms.
Most of the Amaryllidaceae alkaloids may be classified into nine principal skeletally
homogeneous subgroups, although there are several other alkaloids with structures
derived from these main molecular frameworks. Representative alkaloids from