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.
