Lobeline-Synonyms α-Lobeline; Inflatine- obtained from the herb and seeds of Lobelia inflata

B. Lobeline

Synonyms α-Lobeline; Inflatine;

Biological Sources It is obtained from the herb and seeds of Lobelia inflata L., (Lobeliaceae) (Indian Tobacco, Asthma Weed); leaves of Lobelia tupa L. (Campanulaceae) (Tupa, Devil’s Tobacco).

Chemical Structure

[2R-[2α, 6α (S*)]]-2-[6-(2-Hydroxy-2-phenylethyl)-1-methyl-2-piperidinyl]-1-phenylethanone (C₂₂H₂₇NO₂).

Isolation The various steps are as follows:

1. The powdered lobelia herb is moistened with water, acidified slightly with acetic acid and left as such for 3-4 hours. The resulting mass is then pressed and the process of moistening and pressing is repeated subsequently.

2. The acidic solutions thus collected are mixed and rendered alkaline with sodium bicarbonate carefully. The alkaline solution is extracted with ether successively. For purification, the etherial extract is shaken with water, acidified with dilute sulphuric acid. The acidified liquid is again rendered alkaline with sodium bicarbonate solution and shaken with ether.

3. The combined ethereal extract is evaporated and the yellow oily liquid, comprising of the total alkaloids, is dissolved in water, acidified with HCl, filtered and then shaken with chloroform successively. Thus, the chloroform will exclusively extract the lobeline hydrochloride, while leaving the salts of the other alkaloids in the aqueous layer. The chloroform is then evaporated under vacuo to obtain the brownish oily residue.

4. The above residue is then taken up with double its volume of hot water at 80°C. The aqueous solution is kept in a vacuum desiccator over concentrated H₂SO₄ for several hours when lobeline hydrochloride separates out as crystals.

5. To recover the lobeline base, the resulting HCl salt is dissolved in warm water, rendered alkaline with dilute NaOH carefully and extracted with ether several times. The ethereal extract is evaporated and the residue is recrystallized from ethanol or benzene.

Characteristic Features

1. Lobeline is obtained as needles from ethanol, ether and benzene having mp 130-131°C, and specific rotation [α]_D¹⁵  -43^o (ethanol).

2. It is freely soluble in chloroform, ether, benzene and hot ethanol; and very slightly soluble in water and petroleum ether.

Identification Tests

1. Colour Test: Lobeline on the addition of a few drops of concentrated sulphuric acid followed by a drop of formalin solution gives rise to a distinct red colouration.

2. Froehd’s Test: It produces an instant rose red colouration with Froehd’s Reagent that ultimately changes to blue.

3. Erdmann’s Reagent: It develops a faint green colour which intensifies on slight warming.

4. Lobeline Hydrochloride (C₂₂H₂₇NO₂.HCl) (Lobron, Zoolobelin): It is obtained as rosettes of slender needles from ethanol with mp 178-180°C; [α]_D²⁰   -43⁰ (C = 2); and uvmax (methanol) 245, 280 nm (log € 4.08, 3.05). Its solubility profile is as follows: 1 g dissolves in 40 ml of water, 12 ml of ethanol, very soluble in chloroform and very slightly soluble in ether. A 1% (w/v) solution in water has a pH of 4.0-6.0.

5. Lobeline Sulphate [(C₂₂H₂₇NO₂)₂.H₂SO₄] (Lobeton, Unilobin, Bantron, Toban, Lobidan): Its crystals obtained from ethanol exhibits specific rotation[α]_D²⁰  -25^o (C = 2). It is soluble in 30 parts of water and slightly in ethanol.

Uses

1. It is widely used as a respiratory stimulant.

2. Its effects resemble those of nicotine and hence used in lozenges or chewing tablets, containing 0.5-1.5 mg of Lobeline Sulphate, to help in breaking the tobacco habit, otherwise known as ‘smoking deterrants’.
Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar