Senecio vernalis

The known alkaloids senecionine, senkirkine, and retrorsine have been isolated from Senecio vernalis Wald, et Kit. by Roder et al.26 A new alkaloid, named senecivernine (59), was also present. The mass spectrum of (59) showed a molecular ion at m/z 335, and fragment ions at m/z 291, 248, and 220, characteristic for a macrocyclic diester of retronecine, arising from cleavage of the allylic ester.17 Basic hydrolysis of senecivernine gave a new necic acid which had spectroscopic data in accord with the proposed structure. Retronecine was not isolated. The necic acid from senecivernine is a Ci0 acid of an unusual structural type (cf. Vol. 8, p. 55). 

Pyrrolizidine alkaloids in the plant Senecio vernalis have been implicated in the poisoning of cattle.13 The toxic agents in this plant include three closely related alkaloids — senecionine, senkirkin, and seneciphyllin. The structural formula of senecionine is shown in Figure 19.2. 

Figure 9.2. Metabolism of pyrrolizidine alkaloids (PAs) in Senecio vernalis. The substrates for alkaloid biosynthesis, putrescine and spermidine, are derived from primary metabolism. Homospermidine, synthesized by homospermidine synthase (HSS), is the first pathway specific intermediate. It is exclusively incorporated into the necine base moiety of senecionine A-oxide, the backbone structure of all PAs found in this Senecio species. During allocation from the roots as site of synthesis to the shoots, it is chemically modified to provide the species specific PA-pattem.

Moll, S., Anke, S., Kahmann, U., Hansch, R., Hartmann, T., Ober, D. (2002) Cell specific expresssion of homospermidine synthase, the entry enzyme of the pyrroUzidine alkaloids in Senecio vernalis in comparison to its ancestor deoxyhypusine synthase. Plant Physiol, 130, 47-57. 

Senecivernine (63) was isolated from Senecio vernalis The stereochemistry in 63, merenskine (68) and sceleratine (66) °° was determined with X-ray analysis.Inte-gerrimine (64) was isolated from S. integerrinus and Crotalaria incana. The structure of 64 has been determined as the isomer of senecionine (65), differing only in the configuration of the ethylidene group. ... 

Senecio vernalis (senecivernine), 244 Sesbania drummodii seeds (sesbanimide A and sesbanimide B), 182 Sesbania punicea (sesbanimide A and sesbanimide B), 182 sponge Discodermia calyx (calyculin),... 

There are two other examples for the recraitment of genes from primary metabolism. The homospermidine synthase from Senecio vernalis is derived from deoxyh T3usine synthase, an enzyme required for activation of translation factor 5A, and a serine carboxypeptidase-like protein that functions as an acyltransferase in secondary metabolism has been found in Arabidopsis thaliana. 

Fig. 2. Alkaloid biosynthetic pathways are associated with a diverse variety of cell types. The tissue-specific localization (shaded) of enzymes and/or gene transcripts are depicted for the biosynthesis of tropane alkaloids in Atropa belladonna and Hyoscyamus niger roots (A), monoterpenoid indole alkaloids in Catharanthus roseus leaves (B), pyrrolizidine alkaloids in Senecio vernalis roots (C), pyrrolizidine alkaloids in Eupatorium cannabinum roots (D), benzyl-isoquinoline alkaloids in Papaver somniferum vascular bundles (E), and protoberberine alkaloids in Thalictrwn flamtm roots (F).

Pieters LA, Hartmann T, Janssens J, Vlietinck AJ (1989) Comparison of capillary gas chromatography with H an C nuclear magnetic resonance spectroscopy for the quantitation of pyrrolizidine alkaloids from Senecio vernalis. J Chromatogr 462 387-... 

Fig. 19. Alignment of homospermidine synthase (HSS) amino acid sequence from Senecio ver-nalis (Sv) in comparison to deoxyhypusine synthase amino acid sequences from six different species. Sv, Senecio vernalis Nt, Nicotiana tabacumi Hs, Homo sapiens Sc, Saccharomyces cerevisiae Nc, Neurospora crassa Mj, Methanococcus jannaschii. Black boxes denote identical amino acid residues in all seven sequences, framed boxes conservative replacement...

MoU S, Anke S, Kahmann Uet al (2002) Cell-specific expression of homospermidine synthase, the entry enzyme of the pyrrolizidine alkaloid pathway in Senecio vernalis, in comparison with its ancestor, deoxyhypusine synthase. Plant Physiol 130 47-57 Molyneux RJ, PanYT, Goldmann A et al (1993) Calystegins, a novel class of alkaloid glycosidase inhibitors. Arch Biochem Biophys 304 81-88... 

Root cultures of Senecio vulgaris and related species such as S. vernalis and S. erucifolius were used to study PA biosynthesis. These cultures produce sene-cionine N-oxide as the major alkaloid [23,24]. Tracer experiments with radioac-... 

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