Pfizer Handbook of Microbial Metabolites i go 



and irreversible intermediate for the terpenoid side-chain. 

 There was no incorporation of mevalonic acid into the aromatic 

 nucleus. Mevalonic acid also was incorporated exclusively into 

 the isopentene side-chain of auroglaucin. 



Both bacteria and fungi are able to hydroxylate aromatic 

 rings, and the acetate pattern of alternate oxidation often is 

 confused by further oxidations of this sort. 



Other details remain to be determined. The predominance 

 of metabolites indicating derivation from an even number of 

 acetate units has led to speculation concerning a four-carbon 

 intermediate such as acetoacetate. Even larger intermediates 

 have been proposed, such as orsellinic acids as precursors of 

 anthraquinones." So far this possibility has not been ruled out 

 in each case- by rigorous experimental evidence although there 

 is an intuitive tendency to favor the simplest and most flexible 

 unit and to apply the accumulated body of knowledge about in- 

 termediary metabolism. The co-occurrence in a natural source 

 of the anthraquinone and related phenanthrenequinone men- 

 tioned in the introduction to the section on quinones is pre- 

 sumptive evidence against orsellinic acid intermediates, since 

 the two quinone molecules appear to be formed merely by a 

 different mode of folding or arrangement on an enzyme surface 

 of the same intermediate polyketomethylene chain. On the 

 other hand the isolation of such orsellinic acids from isolated 

 fungus members of lichens incapable of completing the anthra- 

 quinone synthesis is interesting. 



The structural relationships (some obvious, others more ob- 

 scure) among the mold products fulvic acid, citromycetin, fu- 

 sarubin, purpurogenone, etc.^- ^' argue in favor of a flexible 

 intermediate in the sense of a single polyketomethylene chain 

 that could be folded and modified in various ways to give re- 

 lated metabolites. Comparison of the structures of the lactone 

 moieties of the macrolide antibiotics with those of the tetracy- 

 clines (both classes of compounds produced by streptomycetes) 

 also seems to point to intermediates of this type. While this is 

 a good working hypothesis, such intermediates have not been 

 isolated and in fact could not long exist in the free state. Per- 

 haps eventually a better knowledge of enzymes will let us know 



" K. Aghoramurthy and T. R. Seshadri, J. Sci. Ind. Research 

 (India) 13A 114 (1954). 



^^ F. M. Dean, R. A. Eade, R. A. Moubasher and A. Robertson, 

 Nature 179 366 (1957). 



"W. B. Whalley, Chem. and Ind., 131 (1958). 



