213 



Depsides and Depsidones 



donia, parmelia and placodium species, grown alone in pure 

 culture, produced no depsides nor depsidones. Orsellinic and 



COOH 



R=H=Orsellinic Acid 



R^CHO=Haematommic Acid 



haematommic acids, simpler moieties which could not be shown 

 to be present as such in the parent lichens, were isolated. This 

 could indicate that these phenols are precursors, and that the 

 algae are necessary to effect coupling as well as final, charac- 

 teristic modifications. It is interesting that orsellinic acid (q.v. ) 

 has been isolated recently from other fungus cultures. Phenolic 

 acids of this sort are obviously acetate-derived. 



Depsidones probably are formed by phenol coupling of the 

 depsides. Phenol coupling (phenol dehydrogenation) is un- 

 doubtedly a widespread phenomenon among natural products. 

 It involves the removal of one electron from the phenol with 

 formation of a phenol-free radical. Such radicals are relatively 

 stable due to the resonance possibilities. In complex natural 

 products such phenol radicals can form new bonds by intra- 

 molecular attack. Thus the formation of a depsidone (in this 

 case protocetraric acid) from a depside might be represented 

 as follows: 



COOH 



COOH 



COOH 



Another example of intramolecular carbon-oxygen coupling was 

 noted earlier in this chapter in the formation of the geodin, 

 griseofulvin type of skeleton. 



Carbon-carbon bonds can be formed similarly (by coupling 



