2.3 Chromone Bitter Principles
The following heterocyclic moieties, such as: chromone, coumarin and coumarone are derived from g-pyrone, α-pyrone and furan nucleus respectively in combination with a benzene nucleus.
Chromone
Coumarin
The important members belonging to the class of chromone bitter principles are, namely: khellin, khellol glucoside and visnagin. These three drug substances shall be described as under:
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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* Wagner’s Reagent: It is a solution of iodine with KI.
2.3.2 Khellol Glucoside
Synonyms Khellinin
Biological Sources It is obtained from the seeds of Ammi visnaga Lam., (Umbelliferae); and also from Eranthis hyemalis L. (Ranunculaceae) upto 0.3%.
Chemical Structure
7-[(β-D-glucopyranosyloxy)-methyl]-4-methoxy-5H-furo [3, 2-g] [1] benzopyran-5-one; (C19H20O10).
Isolation It may be isolated from Eranthis hyemalis by the method put forward by Egger.*
Characteristic Features
1. It is obtained as crystals from ethanol having mp 179°C.
2. It has uvmax (ethanol): 250, 325 nm.
3. It is found to be soluble in acetic acid, hot ethanol slightly soluble in hot methanol; and almost insoluble in acetone, ethyl acetate, ether, chloroform, cold alkali.
Identification Test Khellol glucoside may be identified by making its following tetraacetate derivative due to the presence of four OH moieties.
Khellol Glucoside Tetracetate It is obtained as flakes from ethanol having mp 153°C. It is freely soluble in acetone, ethanol, ethyl acetate; and almost insoluble in petroleum ether.
Uses It is used as a vasodilator.
2.3.3 Visnagin
Synonym Visnacorin.
Biological Sources It is obtained from Ammi visnaga Lam., (Umbelliferae).
Chemical Structure
4-Methoxy-7-methyl-5H-furo [3, 2-g] [1]-benzopyran-5-one; (C13H10O4).
Isolation Various sequential steps involved are as under:
1. The methanol mother-liquor remaining after the isolation of khellin, is evaporated to dryness under vacuo.
2. The resulting residue is taken up in benzene and treated subsequently with petroleum ether, until a distinct turbidity is accomplished.
3. The reaction mixture is cooled, and some small quantum of khellin shall separate out which is removed by filtration.
4. To the filtrate further addition of petroleum ether shall initiate the process of separation of visnagin as different crops that are removed, dried and subjected to distillation under vacuum carefully.
5. The fraction distilling between 150-155°C is collected and visnagin is finally recrystallized from methanol as prigms.
Characteristic Features These are as follows:
1. Visnagin is obtained as thread-like needles from water having mp 142-145°C.
2. It is found to be very slightly soluble in water; sparingly soluble in ethanol; and freely soluble in chloroform.
Identification Tests Visnagin when triturated with a piece of solid KOH or NaOH, it gives rise to a distinct rose-red colour which is certainly lighter in shade than that obtained with khellin.
