Common Mushrooms as Synthetic Geniuses
Yellow pigments with unusual structures from common earthball and peppery bolete?
It's familiar to every child: the common earthball, the mushroom that gives off a cloud of powdery spores when you step on it. The peppery bolete is just as common. However, the substances in these fungi have gone nearly uninvestigated until now. Scientists at the University of Munich have been able to isolate two new yellow pigments with unusual structures from the two species of mushroom.
Researchers are interested in the substances in fungi because they keep finding more and more pharmacologically active substances, which can lead to new antibiotics and cytostatics. One prominent example is the strobilurins, whose strong fungicidal activity makes them useful in evirometally friendly plant protection.
After extracting the chopped up fruiting bodies of common earthballs and performing a complicated purification procedure, the researchers, led by Wolfgang Steglich, found a previously unknown pigment. They named it sclerocitrin, derived from the botanical name of the fungus, scleroderma citrinum. There is an astonishingly large amount of sclerocitrin in ripe earthballs; one kilogram of fresh mushrooms yields up to 400 mg of the bright yellow compound. Further research revealed that sclerocitrin is also one of the main pigments in the bright yellow stem bases and mycelia of another common fungus, the peppery bolete. In addition, the team found another previously unknown yellow pigment, that is closely related to sclerocitrin, in the peppery bolete. This new substance was given the name chalcitrin, which corresponds to the botanical name of the fungus, chalciporus piperatus. These discoveries are a further indication of the strong relationship between earthballs and boletes.
By means of spectroscopic techniques, it was possible to determine the structures of the two new pigments. Both are dimers of a third yellow fungal pigment, xerocomic acid. The researchers have developed a rational hypothesis for the biosynthesis of these and other related pigments. According to them, the common earthball and peppery bolete appear to be synthetic geniuses. Starting from xerocomic acid-which is easily generated from two molecules of the amino acid tyrosine-they produce a series of different dimers in a few synthetic steps.
The two new pigments differ in the central ring system that binds together the two units of xerocomic acid. The Munich chemists now hope to find interesting biological activity in the new substances.
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