Beta-carboline

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β-Carboline (9H-pyrid-[3,4-b]-indole) is an organic amine that is the prototype of a class of compounds known as β-carbolines. β-carboline alkaloids are widespread in plants and animals, and frequently act as monoamine oxidase inhibitors (MAOI). As components of Banisteriopsis caapi, the β-carbolines harmine, harmaline, and tetrahydroharmine play a pivotal role in the pharmacology of the psychedelic brew ayahuasca. Some β-carbolines, notably tryptoline and pinoline, are formed naturally in the human body. The latter is implicated along with melatonin in the role of the pineal gland in regulating the sleep-wake cycle.

The structure of β-carboline is similar to that of tryptamine, with the ethylamine chain re-connected to the indole ring via an extra carbon atom, to produce a three-ringed structure. Indeed, biosynthesis of β-carbolines is believed to follow this route from analogous tryptamines. Different levels of saturation are possible in the third ring, which is indicated here in the structural formula by colouring the optionally double bonds red and blue. Some of the more important β-carbolines are tabulated by structure below.