Pfizer Handbook of Microbial Metabolites 212 



b. DEPSIDES AND DEPSIDONES 



Lichens are symbiotic partnerships of fungi and algae. While 

 this slow-growing combination is visible without the aid of 

 lenses, the extractable metabolites so resemble those of micro- 

 organisms that they are included in this listing for comparison. 



Lichens and the fruiting bodies of the higher fungi were long 

 used in folk medicine in the damp northern lands where they 

 are prominent members of the flora. It was only natural, then, 

 that the tool of organic chemistry was applied at an early date 

 in these locations to elucidate the structures of their metabolites. 

 Thus, historically, a large body of knowledge on such structures 

 existed long before systematic work was begun on the fungi and 

 streptomycetes, which have been so much more rewarding to 

 modem medicine. 



Depsides, e.g. microphyllic acid and olivetoric acid, frequently 

 contain aliphatic side-chains attached to their phenolic rings. 

 The fact that these invariably consisted of an uneven number 

 of carbon atoms was soon recognized and used as a rule in 

 structure determinations. It was considered a curious phenom- 

 enon until it became apparent that such molecules are particu- 

 larly obvious examples of derivation from acetate. 



Certain lichen metabolites, for example some of the anthra- 

 quinone pigments, have been found also in fungi. Moreover, 

 some of the fungal partners have been isolated from lichens and 

 grown alone in pure culture. In a few such cases the same 

 metabolites have been isolated which are produced by the part- 

 nership itself . Examples are the anthraquinones phy scion (pa- 

 rietin) and rhodocladonic acid, the dibenzofurans usnic and 

 didymic acids, as well as pulvic anhydride (stictaurin) and 

 the nidulins.^ - * 



In contrast there is evidence that depsides and depsidones 

 cannot be produced by the isolated fungus partner, but are the 

 unique products of a collaborative effort.* In the work just 

 cited it was found that the fungal components of various cla- 



^ E. Thomas, Beitr. 2. Kryptogamenfiora der Schweiz 9 1 (1939). 



-Hempstead Castle and Flora Kubsch, Arch. Biochem. 23 158 

 (1949). 



^ F. M. Dean, A. D. T. Erni and Alexander Robertson, /. Chem. 

 Soc, 3545 (1956). 



* Dieter Hess, Z. Naturforsch. 14b 345 (1959). 



