Narcissus and Daffodil

178 J. Bastida and F. Viladomat
Crinine – haemanthamine types
The absolute configuration of these alkaloids, which allows both series to be
differentiated, is determined through the circular dichroism spectrum. The
alkaloids of narcissus belong to the haemanthamine type, while in genera such as
Brunsvigia, Boophane, etc., the crinine type alkaloids are predominant. It is also
noteworthy that the alkaloids isolated from narcissus do not show additional
substitutions in the aromatic ring apart from those of C-8 and C-9. On the
contrary, in the genera where crinine type alkaloids predominate, the presence
of compounds with a methoxy substituent at C-7 is quite common. Thus, taking
into account the previous considerations, haemanthamine type alkaloids show
the following characteristics:
1 Two singlets for the para-oriented aromatic protons in the range δ 6.4–7.0
ppm.
2 Using CDCl 3 as the solvent, the magnitude of the coupling constants between
each olefinic proton (H-1 and H-2) and H-3 gives information about the
configuration of the C-3 substituent. Thus, in those alkaloids in which the twocarbon
bridge (C-11 and C-12) was cis to the substituent at C-3, H-1 shows an
allylic coupling with H-3 ( J 1,3 ~1–2 Hz) and H-2 a smaller coupling with H-3
( J 2,3 ~0–1.5 Hz), as occurs in crinamine (53). On the contrary, in the corresponding
C-3 epimeric series, e.g. haemanthamine (49), a larger coupling
between H-2 and H-3 ( J 2,3 5 Hz) is shown, the coupling between H-1 and H-3
not being detectable.
3 It is frequently possible to observe an additional coupling of H-2 with the
equatorial H-4β, in a W-mechanism.
4 The proton H-4α shows a large coupling with H-4a ( J 4∝,4a ~ 13 Hz) due to their
trans-diaxial position, characteristic of the haemanthamine series.
5 Two doublets for an AB system, corresponding to the benzylic protons of
position C-6.
6 The pairs of alkaloids with a hydroxy substituent at C-6, like papyramine/
6-epipapyramine (44/45), haemanthidine/6-epihaemanthidine (51/52), etc.,
appear as a mixture of epimers not separable even by HPLC.
7 Also in relation with position C-6, it is interesting to note that ismine (67), a
catabolic product from the haemanthamine series, shows a restricted rotation
around the biarylic bond, which makes the methylenic protons at the benzylic
position magnetically non-equivalent.
Tazettine type
Although tazettine (58) is one of the most widely distributed alkaloids in the
Amaryllidaceae family, it was found to be an extraction artefact of pretazettine (60)
(Wildman and Bailey, 1967).
The presence of an N-methyl group (2.4–2.5 ppm) in tazettine type alkaloids
immediately distinguishes them from the haemanthamine type, from which they
proceed biosynthetically. Moreover the 1 H-NMR spectrum always shows the signal
corresponding to the methylenedioxy group.