272 ESSENTIAL FATTY ACIDS 



purity for use as analytical standards, and White and Brown^^ and Herb 

 et al}^ have isolated arachidonate by chromatography for the same purpose. 

 Of the methods available, chromatography yields the purest product, but 

 can handle only small amounts. Bromination-debromination is most con- 

 venient for preparing large quantities, but the product contains isomers of 

 the desired unsaturated acid. 



B. SYNTHESIS 



Only linoleic acid of the polyunsaturated acids has yielded to a total 

 synthesis. Noller and Girvin^^ and Baudart^^ have succeeded in the synthe- 

 sis of an unnatural isomer of 9 , 12-octadecadienoic acid by condensation 

 methods. More recently Walborsky et al}^ synthesized natural cis,cis- 

 linoleic acid through acetylenic compounds: 



OCH2 



C5H„C=CCH2Br + BrMgC=C(CH2)7CH _Cu2Br^ 



\ 



OCH2 



OCH2 



/ 

 CsHiiC^C— CH2C=C(CH2)7CH 



\ 



OCH2 



hydro 

 AgNOa 



lysis 



CsHiiC^C— CH2— C=C(CH2)7COOH 



CsHuC^C— CHo— C^C (CH2)7CHO 



xl2 



cis, «s-9, 12-octadecadienoic acid 



This latter synthesis will be useful in the preparation of radioactively 

 labeled linoleic acid for use in pertinent metabolic studies. 



C. COMMERCIAL PREPARATIONS 



The investigator should be critical of the source of commercially available 

 linoleic, linolenic, or arachidonic acids. Products available commercially 

 under the name of linoleic acid are far from pure and in all likelihood are 

 merely corn oil or cottonseed oil fatty acids. One such preparation labeled 

 C.P. linoleic acid was analyzed in the author's laboratory and found to 



IS M. F. White and J. B. Brown, J. Am. Chem. Soc. 70, 4269 (1948). 



1^ S. F. Herb, R. W. Riemenschneider, and J. Donaldson, /. Am. Oil Chemists' Soc. 



28,55 (1951). 

 " C. R. Noller and M. D. Girvin, /. Am. Chem. Soc. 59, 606 (1937). 

 '8 P. Baudart, Bull. soc. chim. [5] 11, 336 (1944). 

 13 H. M. Walborsky, R. H. Davis, and R. Howton, J. Am. Chem. Soc. 73, 2590 (1951). 



