Aporphine alkaloids
Alkaloid chemical compound
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Through Substituent and Biosynthesis
At least 85 aporphine alkaloids have been isolated from plants of 15 families. The best known representative is apomorphine. The aporphine alkaloids are of interest mainly because of their similarity to morphine.
Occurrence
The aporphine alkaloids are most commonly found in plants. For example, isoboldine can be found in the plants in the genera Beilschmiedia, Nandina (Nandina domestica), Glaucium (horn poppy), and other plants. As the name suggests, glaucine was first found in the horn poppy and usually the name of the alkaloids is derived from the plants in which they were first found.
Corydin as a further representative of the aporphine alkaloids is found in Corydalis (larkspurs) Dicentra (heart flowers), and also in the horn poppy.
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Examples
The aporphine alkaloids differ in their substituents and their position on the base structure. Furthermore, their stereochemistry is partly different; most often they are (R)-configured, but glaucine, bulbocapnine, and isothebaine, for example, are (S)-configured.
Biosynthesis
The method by which the central aporphine ring structure is constructed in nature is exemplified by the biosynthesis of bulbocarpin. First, reticuline 1 is oxidized, resulting in a mesomery-stabilized diradical with the boundary structures 2a and 2b. Cyclization results in a fourth six-membered ring, corytuberin 3, which then dehydrates to bulbocapnin 4.
Chemistry
The aporphine alkaloids are of particular interest because of their proximity to morphine and benzylisoquinoline alkaloids. For example, as the name suggests, morphine can be used to produce apomorphine. This can be done by adding an acid under the influence of heat.
The proaporphin alkaloids and the aporphin alkaloids share a framework isomerism.
The aporphine alkaloids usually have a stereocenter.
The (R)-configured glaucine can be synthesized from (S)-glaucine.
Pharmacology
Aporphine alkaloids, including nuciferine, dicentrine, isolaureline, and crebanine, tend to be antagonists or very weak partial agonists of the serotonin 5-HT2A and/or 5-HT2C receptors. However, an exception with higher-efficacy serotonin 5-HT2A receptor agonism is glaucine.
Uses
Apomorphine lowers blood pressure and is also a powerful emetic. It has been used to treat symptoms of Parkinson's disease because of its stimulating effect on dopamine receptors.
Cassytha filiformis, a plant used in African traditional medicine, contains many aporphine alkaloids and that the three main alkaloids actinodaphnin, cassythin, and dicentrin have an in vitro effect on cancer cells.