2.3.1 Khellin
Synonyms Kellin; Kelamin; Kelicor; Keloid; Kelicorin; Khelfren; Gyno khellan; Eskel; Norkel; Amicardine; Ammivisnagen; Viscardan; Visnagen; Visnagalin; Visokellina, Cardio-Khellin; Coronin; Ammivin; Ammipuran; and Ammicardine.
Biological Sources It is the major active chemical constituent obtained from the seeds of Ammi visnaga Lam. (Umbelliferae) (Toothpick Ammi; Chellah; Khella). It is present in the plant substanc to the extent of 1%.
Chemical Structure
4, 9-Dimethoxy-7-methyl-5H-furo [3, 2-g]-[1]-benzopyran 5-one; (C14H12O5).
Khellin is a Furanochromone compound.
Isolation The various steps involved in the isolation of khellin from the seeds of A. visnaga are as stated below:
1. The seeds are dried, powdered, sieved and extracted in Soxhlet apparatus with solvent ether for several hours.
2. The ethereal extract is concentrated in a rotary thin-film evaporator and stored in a refrigerator for a few days.
3. The cold ethereal extract eventually comprise of three distinct layers: an upper green oily layer; a middle cream coloured fatty layer; and a lower green crystalline layer. The upper green oil is removed by filtration with gentle suction, the middle cream coloured fatty layer is removed by the help of petroleum ether, and the remaining lower solid residue is duly purified by repeated crystallization from methanol to obtain pure khellin.
Note: The methanol mother liquor is kept aside for the isolation of ‘visnagin’.
Characteristic Features
1. The crystals of khellin are obtained from methanol having mp 154–155°C.
2. It has a characteristic bitter taste.
3. It boils at bp0.05 180-200°C.
4. It has uvmax (ethanol): 250, 338 nm (E1%1cm 1600, 200).
5. Solubility Profile: Its solubility in g/100 ml at 25°C are: water 0.025; acetone 3.0; methanol 2.6; isopropanol 1.25; ether 0.5; and skellysolve B 0.15.
However, it is found to be much more soluble in hot water and hot methanol.
6. Khellin is observed to be significantly stable when mixed with the normal tabletting excipients.
Identification Tests These are as enumerated below:
1. Khellin decolourizes potassium permanganate solution.
2. When 5-8 mg khellin is mixed with a small piece of solid KOH or NaOH it produces a distinct rose-red colouration.
Note: This test is not positive when either K or Na carbonate/bicarbonate used.
3. Wagner’s Reagent Test: A saturated aqueous solution of khellin yields a precipitate with Wagner’s Reagent.*
4. Khellin gives a faint precipitate with tannic acid solution.
Uses
1. Khellin is used as a potent vasodilator (coronary).
2. It also finds its application as a potent selective bronchodilator.
3. It is used extensively in the treatment and control of coronary insufficiency, angina pectoris and in chronic bronchial asthma.
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