Alkaloidid

Alkaloids are a diverse class of nitrogen-containing natural products, produced by plants and, to a lesser extent, by some microorganisms. They are typically basic and form salts that are soluble in acids. Alkaloids often function as defense compounds against herbivores and pathogens, and many have potent physiological effects in humans and animals.

They are structurally diverse, with common skeletons including indole, isoquinoline, tropane, pyridine, piperidine, and steroidal frameworks. Most alkaloids are biosynthesized from amino acids such as tryptophan, tyrosine, ornithine, or lysine, via enzyme-catalyzed steps that build heterocycles.

Prominent examples range from medicines to poisons, such as morphine and codeine; atropine and scopolamine; quinine; nicotine; cocaine; caffeine; ephedrine; and the vinca alkaloids used in cancer therapy. Their uses span analgesia, anesthesia, antimalarial treatment, stimulants, and anticancer drugs, with toxicity and dependence possible at high doses.

Classification schemes distinguish true alkaloids—nitrogen-containing heterocycles of plant origin—from protoalkaloids, which lack a heterocycle, and pseudoalkaloids, which are amino-acid derivatives that do not fit conventional alkaloid structures.

Chemically, most alkaloids are weak bases and can be isolated as free bases or salts. They are often chiral and may require careful purification. Because of their bioactivity, alkaloids are heavily studied in pharmacology and natural product chemistry.