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.
