170 CARBON METABOLISM III 



formed from it by oxidation arc more closely related biologically 

 than are two differently substituted benzene compounds. The fol- 

 lowing division of the aromatic products synthesized by fungi, taken 

 largely from Raistrick (430), should be considered as a formal classifica- 

 tion only. Examples of the major types are illustrated in Table 4. 



Group I, substituted benzenes, is the largest single group of aromatic 

 compounds, and presents a bewildering array of possible biological 

 interrelations. Some of the members of this group are soluble metab- 

 olites of the culture filtrate, others occur in the mycelium, and still 

 others are associated with reproductive structures (214, 243). 



Members of Group II, substituted benzoquinones, often have an 

 obvious metabolic relation, as oxidation products, to phenolic com- 

 pounds of Group I. Many are derivatives of toluquinone. 



Anthraquinones, Group III, are pigments and are known also in 

 lichens and in higher plants (280). The fungal anthraquinones may 

 be considered as derivatives of chrysophanic acid. 



Group IV, the xanthones, is represented in the fungi by only a few 

 certain examples. Rubrofusarin, formed by Fusarium spp. (389), is 

 probably the same methyl xanthone as asperxanthone of Aspergillus 

 niger (355). 



Group V comprises the naphthoquinones. In addition to javanicin, 

 other fungal products of this type have been identified as products of 

 Fusarium spp. (104, 451) and other fungi (40, 161). Solanione (552) 

 and oxyjavanicin (21) are probably identical with, respectively, javani- 

 cin and fusarubin (63). 



Derivatives of tropolone, Group VI in Table 4, are only quasi- 

 benzenoid, inasmuch as the ring contains seven carbons. Such higher 

 plant products as thujaplicin and colchicine are tropolones (412). An 

 origin of tropolones from phenolic compounds has been suggested 

 (371). 



The depsides, Group VII, are known so far only from lichens; it may 

 be presumed, by analogy with other lichen products (112), that the 

 fungus component of the lichen is responsible for their formation. 



Nidulin illustrates the depsidones (Group VIII). The lichen depsi- 

 dones are similar; some, e.g., gangaleoidin and diploicin, are chlo- 

 rinated, most are not (24). 



The physiological importance of the aromatic compounds is largely 

 unknown, most effort to date having been concentrated on problems 

 of identification. In what follows, three topics will be briefly con- 

 sidered: pathways of biosynthesis, enzymatic transformations, and the 

 possible metabolic significance of the aromatic compounds. 



