Narcissus and Daffodil

Galanthamine extraction 267
The apolar, non-water-miscible solvents tested also led, after alkalisation of
the plant material, to a quantitative extraction of galanthamine. However,
plant material and solvent had to be mixed vigorously, and thorough homogenisation
of the bulbs greatly facilitated the process; without this, the sticky, wet
plant material forms lumps into which the solvent cannot penetrate. The main
advantage of some of the apolar solvents is a selectivity for galanthamine
within the alkaloid fraction. For example, using chloroform for primary
extraction, alkaloids were completely extracted. Using n-heptane, n-hexane or
n-pentane for extraction, an alkaloid fraction was obtained in which galanthamine
and haemanthamine were significantly enriched. For the following tests
n-heptane was chosen, since it is less toxic and less inflammable than n-hexane or
n-pentane.
The solubility of the galanthamine base is remarkable: it can be extracted with
polar solvents such as methanol as well as with apolar solvents such as n-heptane.
A possible explanation for this is the formation of intramolecular hydrogen bonds
between the hydroxyl proton and the oxygen atom of the ether group, which
makes the molecule less hydrophilic for the solvent in apolar solvents (Carroll,
1990). In polar solvents intermolecular hydrogen bonds can be formed which
explain its solubility in this group of solvents.
Optimum pH for extraction
Since alkaloids may be very different in their basicity, the optimum pH value for
the following liquid-liquid separations was studied. The crude alkaloid fraction
was obtained by extraction with chloroform after alkalisation of the crushed
plant material with sodium carbonate solution. The organic phase was extracted
with diluted sulphuric acid and the resulting aqueous phase was adjusted to pH
5.0 with diluted ammonia. The aqueous phase was extracted five times with
diethyl ether. The pH of the aqueous solution was adjusted to pH 6.0 and the
extraction was repeated five times using diethyl ether. The procedure was
repeated in steps of one pH unit until pH 12.0 was reached. The resultant ether
fractions (mainly alkaloids) were analysed by HPLC. It was shown that, at pH 5,
galanthamine was not found in relevant amounts in the diethyl ether fraction.
However many other substances, including several alkaloids, could be separated
at this pH value. At pH values >6.0, galanthamine was found in larger amounts
in the organic phase. At pH values >9.0, galanthamine was extracted quantitatively
from the aqueous phase, in contrast to several very basic alkaloids which
still remained in the aqueous phase at pH 9.0. It was concluded that, for a technical
extraction of galanthamine from Narcissus ‘Carlton’, other alkaloids should
be removed at pH 5.0 by extraction with an organic solvent, before a quantitative
extraction of galanthamine from the aqueous phase at pH 9.0 with the
organic solvent, is carried out.
Selective crystallisation of galanthamine from the alkaloid mixture
A series of tests with many commercially available solvents was conducted to find
a suitable solvent for the crystallisation of pure galanthamine from the alkaloid