Fungi are one of a number of species producing lots of secondary metabolites with a wide spectrum of biological activity. One of the latest to be isolated and identified is Dhilirolide L which is a member of a family of about 14 meroterpenoids possessing an unusual ring system. Anderson etal reported its structure in the Journal of Organic Chemistry. The structure of one of this class is shown below:
The authors investigated the fungus Penicillium purpurogenum isolated from fruit of the tree Averrhoa bilimbi The mature fruit of A. bilimbi is susceptible to infection by P. purpurogenum, which can lead to complete decay of individual pieces of fruit. It also seems as if insects do not like this particular fungus either as it stops development and feeding of the cabbage looper which is a virulent agricultural pest found in Sri Lanka.
So after culturing the fungus in, or should it be on, dextrose agar (50 petri dishes worth) it was cut into small pieces and extracted with ethyl acetate. This was concentrated and the residue chromatographed extensively on Sephadex LH20 and then on reverse phase silica. This ultimately produced the desired compounds in yields ranging from 30mg to 0.5mg. Structure determination followed, including x-ray and out popped the structures similar to the one above. These were tested for their efficacy against the insect and dhilirolide L proved to be the most active. The authors also fed the fungus 13C labelled acetate thus enabling them to propose a biosynthetic route for their formation.
The work of these “isolationists” is tremendous and requires as much patience as a synthetic chemist needs for a total synthesis. I admire their work and extensive knowledge of structural methodology. One question remains, why does the fungus produce such a complicated structure to dispose of an insect pest? Anyone?
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