Aconitine-It is obtained from the dried roots of Aconitum napellus Linn

B. Aconitine

Biological Source: It is obtained from the dried roots of Aconitum napellus Linn. (Ranunculaceae) and other aconites. A. napellus in also known as aconite, blue rocket and monkshood. Usually it contains upto 0.6% of the total alkaloids of aconite, of which approximately one third is the alkaloid aconitine.

Chemical Structure

(1α, 3α, 6α, 14α, 15α, 16(β)-20-Ethyl-1, 6,-16-trimethoxy-4-(methoxymethyl) aconitane-3, 8, 13, 14, 15,-pentol 8-acetate 14-benzoate (C₃₄H₄₇NO₁₁).

Characteristic Features

1. It occurs as hexagonal plates having mp 204°C.

2. Its pKa value stands at 5.88.

3. Its specific rotation [α]_D + 17.3° (Chloroform).

4. It is slightly soluble in petroleum ether; but 1 g dissolves in 2 ml chloroform, 7 ml benzene, 28ml absolute ethanol, 50 ml ether, 3300 ml water.

Identification Tests Aconitine forms specific salts with HBr and HNO₃ having the following physical parameters.

(a) Aconitine Hydrobromide Hemipentahydrate (C₃₄H₄₇O₁₁.HBr.2½ H2O): The hexagonal tablets mp 200-207°C and the dried substance mp 115-120°C. Its crystals obtained from ethanol and ether with ½ H2O has mp 206-207°C. Its specific rotation [α]_D – 30.9°.

(b) Aconitine Nitrate (C₃₄H₄₇NO₁₁.HNO₃): The crystals have mp about 200°C (decomposes), [α]_D²⁰ -35⁰(c = 2 in H₂O).

Uses

1. It is exclusively used in producing heart arrythmia in experimental animals.

2. It has also been used topically in neuralgia.

Biosynthesis of Aconitine-Type Alkaloids Aconite is particularly regarded as extremely toxic, due to the presence of aconitine, and closely related C₁₉ nonditerpenoid alkaloids. It has been observed that the species of Delphinium accumulate diterpenoid alkaloids, for instance: atisine, which proved to be much less toxic when compared to aconitine. A vivid close resemblance of their structural relationship to diterpenes, such as: ent-kaurene, of course, little experimental evidence is available.

From the above course of reactions it appears quite feasible that:

(a) A pre-ent-kaurene carbocation usually undergoes Wagner-Meerwein Rearrangements,

(b) The atisine-skeleton is produced subsequently by incorporating an N–CH₂–CH₂–O fragment (e.g., from 2-aminoethanol) to form the resulting heterocyclic rings,

(c) The aconitine-skeleton is perhaps formed from the atisine-skeleton by further modifications as stated above,

(d) A rearrangement process converts two fused 6-membered rings into a (7 + 5)-membered bicyclic system, and

(e) One carbon from the exocyclic double bond is eliminated.
Source:Pharmacognosy And Pharmacobiotechnology By Ashutosh Kar