Pfizer Handbook of Microbial Metabolites 214 



of the ortho and para resonance isomers of the phenol-free 

 radical). Biphenyl, binaphthyl and fois-anthraquinone skele- 

 tons might be formed in this way. 



A combination of the two types of bond formation (i.e. first 

 an intermolecular carbon-carbon coupling followed by an intra- 

 molecular oxygen-carbon coupling) probably occurs in the bio- 

 synthesis of compounds such as the dibenzofurans, etc. 



More thorough considerations of phenol coupling as a bio- 

 synthetic process have been published. ' '' 



In vitro couplings of phenolic compounds have been accom- 

 plished in the laboratory, by using simple electron acceptors 

 such as molecular oxygen or ferric chloride, and natural prod- 

 ucts have been prepared in this way. Yields under such condi- 

 tions are generally low, and the orienting influence of the en- 

 zyme surface seems to be required for real efficiency. 



Referencing of this section is lean because of the very thor- 

 ough existing work.' In general the final structure determina- 

 tion or synthesis is mentioned. 



441 Diploicin, C16H10O5CI4, colorless crystals, m.p. 232°. 



^' OCH. 



CI '-' CH3 



Buellia canescens (Dicks.) DeNot. 



Thomas J. Nolan, Joseph Algara, Eugene P. McCann, Wm. 

 A. Manahan and Niall Nolan, Sci. Proc. Roy. Dublin Soc. 24 

 319 (1948). 



442 Variolaric Acid (Ochrolechaic Acid, Parellic Acid), C16H10O7, 

 colorless crystals, m.p. 296°. 



OH 



^D. H. R. Barton and T. Cohen, Festschrift Arthur Stoll, 111 

 (1957). 



** Holger Erdtman and Carl Axel Wachmeister, ibid., 144 (1957). 



" Yasuhlko Asahina and Shoji Shibata, "Chemistry of Lichen Sub- 

 stances," Japan Society for the Promotion of Science, Tokyo, 1954. 

 (In English) 



