The mysterious cembranoids

I have said before that nature is the best chemist. There is a wide variety of chemicals produced by living organisms that are used as weapons; some for defense and some for predation. Alternatively, some of these substances may be used to attract a mate; some plants even use chemicals to lure other organisms, like insects, so they can serve as pollinating agents. In insect societies like the ones represented by ants and termites, chemicals are used as a means of communication. The study of the interaction of chemicals and living organisms is an aspect of chemical ecology. The development of this scientific discipline has provided us with a wide variety of interesting chemical structures that have proven useful in both fundamental research and in practical applications as well.

One of the most interesting types of natural products are the cembranoids. These compounds were first described about 50 years ago, and they represent some of the more widespread type of compounds in nature, so it is strange that this kind of compounds is not widely known outside organic chemist’s circles. But before we go any further, what is a cembranoid? All members of this class of compounds display a chemical structure called a “cembrene” ring (below).

I love chemical structures…

This 14-carbon ring is the basis for more than 300 different naturally-occurring cembranoids that have been described. Here are some more examples:

As I said before, these compounds are widely distributed in nature. Cembranoids have been isolated from plants, like conifers and tobacco. They are also found in insects such as ants, where they show pheromone-like action and in termites, where they are part of their chemical defense mechanism. Cembranoids are not limited to plants or invertebrates, having also been found in the paracloacal glands of the male Chinese alligator (Alligator sinensis). Marine invertebrates are the richest cembranoid source having provided hundreds cembranoid derivatives. Most of these were isolated from West Indian gorgonians, in which cembranoids comprise about 25% of their total discovered metabolites.

Relatively few biological effects of the cembranoids have been described, but the most accepted interpretation is that they represent defensive molecules. Biochemically, cembranoids form corals are known to act as antitumor compounds. Tobacco plants also produce cembranoids, where they are responsible for the characteristic aroma of tobacco products. These tobacco cembranoids have been reported to inhibit prostaglandin synthesis in vitro, suggesting possible antiinflamatory effects. Also, some cembranoids seem to be neuroprotective, preventing cell death in animal models for stroke.

Some cembranoids have been found to inhibit the effects of nicotine, one of the most addictive substances known. Interestingly, one of the cembranoids (in red, above) capable of preventing the nicotine effects is produced in tobacco plants, the same source of nicotine!

Why would a plant produce two types of substances which may act as physiological antagonists of each other? This is kind or weird when you think about it; like giving a poison and its antidote at the same time. The physiological / evolutionary significance of the presence of these two substances in tobacco plants is a very interesting area of research which is currently under intensive study. Stay tuned!

If you want to know more

Eisner T and Meinwald J (eds.) Chemical Ecology: The Chemistry of Biotic Interaction. National Academy Press, Washington D.C. 1995.

Ferchmin PA et al. (2009) Actions of octocoral and tobacco cembranoids on nicotinic receptors. Toxicon 54:1174-1182.



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