Alkaloids
Introduction
Alkaloids are a group of naturally occurring chemical compounds that mostly contain basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar structure may also be termed alkaloids. In addition to carbon, hydrogen and nitrogen, alkaloids may also contain oxygen, sulfur and more rarely other elements such as chlorine, bromine, and phosphorus.
Classification
Alkaloids are classified according to their chemical structure (such as indole, isoquinoline, and pyridine alkaloids) and also by their biological precursor (such as ornithine, lysine, tyrosine, tryptophan, and anthranilate). Some alkaloids are toxic to other organisms. They often have pharmacological effects and are used as medications, as recreational drugs, or in entheogenic rituals. Examples are the local anesthetic and stimulant cocaine; the psychedelic psilocin; the stimulant caffeine; nicotine; the analgesic morphine; the antibacterial berberine; the anticancer compound vincristine; the antihypertension agent reserpine; the cholinomimetic galantamine; the spasmolysis agent atropine; the vasodilator vincamine; the anti-arrhythmia compound quinidine; the anti-asthma therapeutic ephedrine; and the antimalarial drug quinine.
Biosynthesis
Alkaloids are produced by a large variety of organisms, including bacteria, fungi, plants, and animals, and are part of the group of natural products (also called secondary metabolites). Many alkaloids can be purified from crude extracts by acid-base extraction. Many alkaloids are toxic to other organisms. They often have pharmacological effects and are used as medications, as recreational drugs, or in entheogenic rituals. Examples are the local anesthetic and stimulant cocaine; the psychedelic psilocin; the stimulant caffeine; nicotine; the analgesic morphine; the antibacterial berberine; the anticancer compound vincristine; the antihypertension agent reserpine; the cholinomimetic galantamine; the spasmolysis agent atropine; the vasodilator vincamine; the anti-arrhythmia compound quinidine; the anti-asthma therapeutic ephedrine; and the antimalarial drug quinine.
Alkaloid Nomenclature
The nomenclature of alkaloids is complex and stems from the chemical names of the alkaloids, their botanical names, their common names, and certain chemical reactions that they undergo. The International Union of Pure and Applied Chemistry (IUPAC) has developed a systematic nomenclature, but it is not widely accepted and most alkaloids are still known by their common or trivial names.
Alkaloids in Medicine
Many alkaloids have found use in modern medicine: their isolation from plants and the study of their structure has been of immense value to medicinal chemistry. Many synthetic and semi-synthetic drugs are structural modifications of the alkaloids, which were designed to enhance or change the primary effect of the drug and reduce unwanted side-effects. For example, naloxone, an antagonist to the opioid receptors, is a derivative of thebaine that is present in opium.