D. Lobelanidine
Biological Source It is same as that of lobelanine.
Chemical Structure
Isolation It is obtained as one of the fractions obtained from the column chromatography of the aqueous extract from step (3) under isolation of lobeline.
Characteristic Features
1. It is obtained as scales from ethanol with mp 150°C.
2. It distils unchanged in vacuo.
3. It is freely soluble in benzene, chloroform, acetone; slightly soluble in ether, petroleum ether; and almost insoluble in water.
Identification Tests
1. Lobelanidine Hydrochloride (C22H29NO2 . HCl): It is obtained as needles from ethanol having mp 135-138°C.
2. Lobelanidine Hydrobromide (C22H29NO2.HBr): Its crystals have a mp 189°C.
Synthesis from Lobeline, Lobelanine and Lobelanidine First of all, lobelanine may be synthesized by the interaction of one molecule of glutaric dialdehyde, two moles of benzoyl acetic acid, and one mole of methylamine hydrochloride; allowing the reaction mixture to stand for 40 hours at 35°C and at pH 4.5. Thus, the resulting product lobelanine gives rise to:
(a) Lobeline: When subjected to partial reduction, and
(b) Lobelanidine: On being subjected to complete reduction.
All these reactions are summarized as given below.
Biosynthesis of Lobeline and Lobelanine The two above stated alkaloids, namely: lobeline and lobelanine, commonly found in the antiasthmatic medicinal plant Lobelia inflata, found to comprise of the piperidine rings with alternative C6C2 side-chains derived from phenylalanine via cinnamic acid. In fact, these alkaloids are formed as shown below wherein benzoylacetyl-CoA, an emerging intermediate in the b-oxidation of cinnamic acid helps to cater for the nucleophile engaged in the
Mannich reaction. Thus, oxidation of the piperidine ring brings forth a new iminium species that can react further with a second mole of benzoylacetyl-CoA, again via Mannich reaction. Both lobeline and lobelanine are the resulting products obtained from further N-methylation and/or carbonyl reduction reactions.
