alkaloid

Alkaloids are a diverse class of naturally occurring organic compounds that contain one or more basic nitrogen atoms, usually in heterocyclic rings. They are predominantly produced by plants as secondary metabolites, though some fungi, bacteria, and animals synthesize them as well. Because of their basic nitrogen, many alkaloids form salts with acids and are often soluble in organic solvents. They frequently exhibit potent pharmacological effects in humans and animals, even at low doses.

Biosynthesis and occurrence: Alkaloids are typically derived from amino acids such as tryptophan, tyrosine, phenylalanine, ornithine, or lysine, and are shaped by cyclization and other transformations into diverse ring systems. They occur widely in plants, especially in families such as Solanaceae, Rubiaceae, and Papaveraceae, and they are also produced by some fungi and bacteria. Many alkaloids serve ecological roles as defense compounds against herbivores and pathogens.

Classification and examples: Alkaloids are commonly grouped by their core ring systems. Indole alkaloids include reserpine and yohimbine. Isoquinoline alkaloids include morphine, codeine, and berberine. Tropane alkaloids include atropine and scopolamine. Other notable alkaloids include caffeine and theobromine (purine alkaloids), quinine and quinidine (quinoline alkaloids), and nicotine (pyridine alkaloid).

Applications and safety: Many alkaloids have important medical uses as analgesics, anesthetics, antimalarials, anticholinergics, stimulants, or bronchodilators. However, they can be highly toxic and have potential for dependence or abuse. Several are regulated as controlled substances (for example morphine, cocaine). Research continues to explore their biosynthesis, ecological roles, and therapeutic potential.