Alkaloids

Alkaloids are a heterogeneous group of natural organic compounds that occur in many plants, animals, fungi and microorganisms.

Definition and structure

Nitrogen-containing compounds: Alkaloids contain at least one nitrogen atom, which is usually incorporated into a heterocyclic ring system. This structure gives them basic properties, which means that they can absorb protons and therefore carry a positive charge.

Occurrence: Over 10,000 different alkaloids are known to occur, mainly in higher plants, particularly in families such as the poppy family (e.g. morphine), nightshade family (e.g. nicotine) and papilionaceous plants (e.g. quinoa).

Classification of alkaloids

Alkaloids can be classified according to their chemical structure or their effects:

By chemical structure:

• Pyridine alkaloids: For example nicotine.
• Isoquinoline alkaloids: For example morphine and codeine.
• Tropane alkaloids: For example, atropine and scopolamine.
• Indole alkaloids: For example psilocybin and serotonin.

After effect:

• Analgesics: Morphine, codeine.
• Stimulants: caffeine, cocaine.
• Antimalarial agent: quinine.
• Hallucinogens: psilocybin, mescaline.

Effects of alkaloids

Alkaloids often have strong effects on the human and animal organism. They can cause both therapeutic and toxic effects. Examples are

• Morphine: A strong painkiller.
• Caffeine: A stimulant of the central nervous system.
• Nicotine: Has stimulating properties and can be addictive.

Functions in nature

Plant defense: Alkaloids often serve as a defense against predators and diseases. Their bitterness can deter animals, while their toxic properties repel many insects.

Medicinal use: Alkaloids have a long history of medicinal use. Many alkaloids are still used in pharmacy today, both as medicines and in research to develop new therapeutic approaches.

• Pain relief: Morphine is often used to treat severe pain.
• Anesthesia: Cocaine is used as a local anesthetic, especially in ophthalmology.
• Antidepressants: Some alkaloids have mood-enhancing properties and are used in psychiatry.
• Blood pressure regulation: Rauwolfia alkaloids such as reserpine are used to treat high blood pressure.

Toxicity and side effects

The toxic effects of alkaloids can be serious:

• Overdose: Many alkaloids are toxic in high doses. Symptoms can range from nausea and cramps to respiratory arrest.
• Dependency potential: Some alkaloids, such as nicotine and morphine, have a high dependency potential and can lead to serious health problems if abused.

Research and development

The structure-activity relationship (SAR) plays an important role in pharmaceutical research. By understanding how small changes in the chemical structure can influence the effect of an alkaloid, work is being done on the development of new drugs. Innovative technologies such as computer-aided drug design help to identify new compounds that target specific receptors in the body.