B. Senecionine
Synonym Aureine;
Biological Source The hepatotoxic alkaloid is obtained from the whole plant of Senecio vulgaris L. (Compositae); weed of Senecio aureus L. (Asteraceae) (Squaw Weed, Liferoot, Golden Groundsel); and preblooming plant of Tussilago farfara L. (Asteraceae) (Coltsfoot, Coughwort, Horse-Hoof).
Chemical Structure
12-Hydroxysenecionan-11, 16-dione; (C18H25NO5): is described by Barger and Blackie (1936).*
Characteristic Features
1. It is obtained as plates having mp 236°C and a bitter taste.
2. Its specific optical rotation [α ]D25 -55.10 (C = 0.034 in chloroform).
3. It is practically insoluble in water; freely soluble in chloroform; and slightly soluble in ether and ethanol.
Uses
1. It is used as an excellent drug to control pulmonary hemorrhage.
2. It is also used to hasten labour and check the pains of parturition.
Biosynthesis of Retronecine and Senecionine It has been observed that the plants synthesizing the above mentioned pyrrolizidine alkaloids seem to be devoid of the decarboxylase enzyme transforming ornithine into putrescine; in fact, ornithine is actually incorporated by way of arginine.
The various steps involved essentially in the biosynthesis of retronecine and senecionine are summarized as below:
1. Two moles of putrescine are condensed in an NAD+-dependent oxidative deamination reaction to yield the corresponding imine, which is subsequently transformed into homospermidine by the aid of NADH reduction.
2. The genesis of the creation of the pyrrolizidine skeleton is on account of the homospermidine molecule by a sequential series of interactions, such as: oxidative deamination, imine formation, intramolecular Mannich reaction, that specifically exploits the enolate anion produced from the aldehyde.
3. The ‘pyrrolizidine skeleton’ thus provides a C4N unit from ornithine, together with an additional four C-atoms from the same amino acid precursor.
4. The senecionine is a diester of retronecine with senecic acid.
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* Barger, Blackie, J. Chem. Soc. 743 (1936)
