2.6.1 Picrotoxin
Synonym Cocculin.
Biological Sources It is obtained as the bitter principle from the seed of Anamirta cocculus L. Wight & Arn. (Menispermaceae); and also found in Tinomiscium philippinense Diels.
Chemical Structure Picrotoxin is a molecular compound of one mole picrotoxinin (C15H16O6), q.v., and one mole picrotin (C15H18O7), q.v., into which it is readily separated. Thus, picrotoxin may be resolved into the two components by boiling with 20 parts of benzene. In this manner, picrotoxinin remains dissolved in benzene whereas picrotin that is practically insoluble in benzene can be separated easily. Likewise, this cleavage may also be accomplished by chloroform more efficiently. Thus, we have:
Isolation Various steps involved in the isolation of picrotoxin are:
1. The seeds are dried, powdered coarsely, sieved and defatted with petroleum ether in a Soxhlet apparatus.
2. The defatted powder (marc) is subsequently extracted by boiling with ethanol or with water.
3. The filtrate thus obtained is treated with lead acetate solution (5% w/v), filtered and the excess of ‘lead’ is removed by passing freshly generated H2S gas (i.e., Pb is precipitated as PbS).
4. The resulting solution is filtered, residue discarded and the filtrate is concentrated to a syrupy consistency in a Rotary Thin Film Evaporator. The syrupy liquid is kept in a refrigerator overnight.
5. Picrotoxin crystallizes out as a crude substance.
6. It may be further purified by treating with ethanol or boiling water and activated charcoal powder to obtain the pure substance.
Characteristic Features
1. It is obtained as shiny rhomboid leaflets mp 203°C.
2. It has an intense bitter taste and is extremely poisonous.
3. It has specific optical rotation [α]16D – 29.3° (C = 4 in absolute ethanol).
4. Solubility Profile: 1 g dissolves in 150 ml cold water; 45 ml boiling water, in 13.5 ml 95% ethanol, in 3 ml boiling ethanol; sparingly soluble in ether, chloroform; and readily soluble in aqueous solution of NaOH and in strong NH4OH.
5. It is highly toxic to fish.
6. It is stable in air, but is affected by light.
7. Picrotoxin is almost neutral to litmus.
Identification Tests These are as stated below:
1. Sulphuric Acid Test: Dissolve 2-3 mg of picrotoxin in a few drops of sulphuric acid, a goldenyellow-colour is produced that gets changed to reddish-brown gradually.
2. Anisaldehyde Test: Moisten a few crystals of picrotoxin with H2SO4 and just add 1-2 drops of a solution of anisaldehyde in dehydrated ethanol (1 : 5), a permanent blue colouration is produced.
3. Potassium-Cupric Tartrate Test: Add about 5-10 mg of picrotoxin to 2 ml of potassiumcupric tartrate solution (0.5%) with 10 ml of water, a red precipitate is formed gradually in the
cold, but a little faster on warming.
4. Vanillin HCl Test: A few mg of picrotoxin when boiled with vanillin hydrochloride solution (0.1% w/v) it gives rise to a green colouration.
5. Reduction Tests: Picrotoxin reduces Fehling’s solution to give a brick-red precipitate; and Tollen’s reagent to give a silver mirror.
6. Mix 0.2 g KNO3 with four drops of H2SO4 in an evaporating dish. Sprinkle a few crystals of picrotoxin on the resulting mixture and add dropwise NaOH solution (2N), until it is present in a little excess quantity. The crystals of picrotoxin shall initially acquire a red colouration that fades out slowly.
Uses
1. It is used as a CNS-stimulant. Therefore, it may be employed intravenously as an antidote in barbiturate poisoning and other narcotics also.
2. It also finds its application as an effective respiratory stimulant.
3. Very small quantities of the powdered seeds are sufficient to stupify fish.
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* Rotenoids: The rotenoids take their name from the first known example rotenone and are usually generated by ring
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