Cactus alkaloids

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Cactus alkaloids are natural chemicals found in cacti. They fall into two main groups: phenethylamines and tetrahydroisoquinolines. The cactus family, especially the genus Lophophora, contains many of these compounds—more than 40 have been identified in Lophophora.

In Lophophora williamsii (peyote), mescaline is the most abundant alkaloid, with pellotine also present. In Lophophora diffusa and Lophophora fricii, pellotine is the main alkaloid; L. diffusa also has anhalamine, and L. fricii has anhalonidine.

Outside Lophophora, cactus alkaloids are less common, but some species contain mescaline, pellotine, or other related compounds such as hordenine or N-methyltyramine. Some psychoactive cacti are in the genus Echinopsis, including the San Pedro cactus.

Biosynthesis starts from the amino acid tyrosine and proceeds through tyramine and dopamine. By adding hydroxy groups and methylating them, mescaline is formed. A tetrahydroisoquinoline ring can be built from mescaline-related intermediates to make anhalamine and anhalonidine. Anhalonidine can become anhaline when a benzodioxole unit forms. Further methylation of the dopamine amino group can lead to pellotine and then lophophorin.

Chemists have several ways to synthesize these alkaloids. For the tetrahydroisoquinoline ring, a common method is the Bischler-Napieralski reaction. Starting from mescaline, researchers can make anhalamine, anhalidine, anhalonidine, and pellotine, among other compounds.

Mescaline is a psychedelic and is mainly responsible for the hallucinogenic effects of peyote. The other cactus alkaloids usually have milder effects and may have anticonvulsant properties. Pellotine was once used as a sedative in the early 20th century.