Allopumiliotoxin

Allopumiliotoxins are a structural division in the pumiliotoxin-A class of alkaloids. The compounds of the pumiliotoxin-A class are primarily found in the skins of frogs, toads, and other amphibians and are used as a chemical defense mechanism to ward off predators, microorganisms, and ectoparasites. The compounds were originally discovered in neotropical dendrobatid frogs, but are also found in the mantellid frogs of Madagascar, myobatrachid frogs of Australia, and bufonid toad of South America. Frogs possessing this defense mechanism have aposematic coloring.

The poison-dart frog family Dendrobatidae has yielded many different alkaloids categorized into several different classes, almost all of which have shown high pharmacological activity on muscle and nerve cells.

The pumiliotoxin-A class, specifically, contains many molecules which have had a favorable effect on the heart. Allopumiliotoxins, the most complex member of this class, have a wide range of biological activities, the full understanding of which has not been fully discerned due their incredible complexity and subsequent synthetic difficulties. Among allopumiliotoxins, those with a β-oriented C-7 hydroxyl group have shown greater activity in comparison to α-epimers of this position. Allopumiliotoxin 339A has been shown to stimulate sodium influx and phosphoinositide breakdown in the cerebral cortical synaptoneurosomes of guinea pigs and is one of the most active allopumiliotoxins. It is more biologically active than pumiliotoxin B, which has had similar biological effects on the secondary messenger system, causing muscle rigidity and some favorable effects on the heart.

Pumiliotoxins and allopumiliotoxins are very toxic in general. Pumiliotoxin B has caused death in mice when 20 μg was given in injections below the skin

There are three divisions within the pumiliotoxin-A class: allopumiliotoxins, pumiliotoxins, and homopumiliotoxins. Once the compound’s specific class is determined, it’s given a number based on its molecular weight. These biologically active compounds are complex and have structural variations that allow for specific molecular recognition. Therefore, the way 2 isomers are differentiated is by a letter after the number. Therefore, for example, allopumiliotoxin 339A is an allopumiliotoxin with a molecular weight of 339 g/mol but there are other isomers with the same molecular weight. Allopumiliotoxin 339A has an axially oriented hydroxyl group at the 7-position in the indolizidine nucleus that differentiates it from allopumiliotoxin 339B. A (+) or (-) sign preceding the name of an allopumiliotoxin refers to the compound’s optical activity. Compounds that rotate a plane of polarized light clockwise are referred to as dextrorotatory and are preceded by a (+) sign. Compounds that rotate a plane of polarized light counterclockwise are referred to as levorotatory and are preceded by a (-) sign.

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