Tropane alkaloids

Tropane alkaloids are a class of alkaloids and secondary metabolites that feature a tropane ring in their chemical structure. These compounds are predominantly found in plants of the family Solanaceae, which includes well-known species such as belladonna, henbane, and mandrake. Tropane alkaloids are known for their effects on the nervous system, many of which are used medicinally as well as being recognized for their toxic properties.

Chemical Structure

Tropane alkaloids contain a bicyclic structure derived from pyrrolidine and piperidine, known as the tropane ring. This structure is characterized by a seven-membered ring system that includes nitrogen. The most common tropane alkaloids, such as atropine, scopolamine, and cocaine, vary in their functional groups attached to the tropane ring, which significantly influences their pharmacological properties.

Biosynthesis

The biosynthesis of tropane alkaloids in plants begins with the amino acid ornithine or arginine. These amino acids undergo a series of enzymatic transformations to form the tropane ring. The pathway involves several steps, including the formation of putrescine, which is then converted into N-methylputrescine. Subsequent oxidation and methylation reactions lead to the formation of the tropane skeleton.

Pharmacology

Tropane alkaloids act primarily on the muscarinic acetylcholine receptors in the nervous system. They are known for their anticholinergic properties, blocking the action of the neurotransmitter acetylcholine. This action results in various physiological effects, such as increased heart rate, dilation of the pupils, and decreased secretion of bodily fluids.

Medical Uses

Some tropane alkaloids have important medical applications. For example:

• Atropine is used to increase heart rate in bradycardia (slow heart rate) and as a preoperative medication to reduce salivation.
• Scopolamine is used for motion sickness and as an adjunct to anesthesia.
• Cocaine has a history of use as a local anesthetic, particularly in ophthalmology.

Toxicity and Safety

While some tropane alkaloids have medicinal value, they can be highly toxic at higher doses. Symptoms of tropane alkaloid poisoning include dry mouth, difficulty swallowing, dilated pupils, tachycardia, hallucinations, and potentially death. Plants containing these alkaloids have historically been used as poisons.

Cultural and Historical Aspects

Tropane alkaloid-containing plants have been used in various cultural rituals and folklore for their psychoactive and hallucinogenic effects. For example, the use of belladonna and mandrake in witchcraft and magic potions is well documented in European folklore.

See Also

• Alkaloid
• Solanaceae
• Psychoactive drug
• Poisonous plants