CLASSIFICATION AND STUUCTUHE OF FATTV ACIDS 25 



MacLean^^ do not agree with the interpretation of the above investigators 

 as to the structure of arachidonic acid. 



Arachidonic acid is the only 20-carbon acid wliich is ordinarily detectable 

 in normal animal fat. Its saturated derivative, arachidic acid, has been 

 reported in hog fat, after the excessive ingestion of peanuts,*^ since peanut 

 oil is an excellent source of this fatty acid. 



The source of the arachidonic acid normally present in the animal 

 lipids is undetermined. It is not believed that the animal body can de- 

 saturate the ordinary saturated fats to this extent, and moreover ara- 

 chidic acid is not ordinarily a component of food fats. Since arachidonic / 

 acid belongs to the category of essential fatty acids,^-"^" it is obvious that it I 

 cannot be synthesized in the animal body de novo. "^ 



{6) Ethynoic Acids 



This class of compounds includes acids which contain a triple bond. 

 Although many ethynoic (or ethinoic) acids have been prepared syntheti- 

 cally, only two are components of natural fats. Most of the triple-bonded 

 acids which are known have the unsaturated linkage either at the a or co 

 position in the hydrocai'bon chain, as for example propyolic or a-propynoic 

 acid, HC : CCOOH, and dehydroundecylinic or co-undecynoic acid, HC : C- 

 (CH2)8COOH. In the case of the three naturally occurring acids which 

 have 18 carbons, the unsaturated linkage (or linkages) occur elsewhere in 

 the molecule. The octadecynoic acids are frequently referred to as stear- 

 olic acids. 



a. Tariric Acid. Arnaud*'''*^ was the first to prepare tariric acid from 

 tariri seed or bitterbush oil (Picramnia Sow). It is 6-octadecynoic acid; 

 however, it is more frequently referred to as 6-stearolic acid. The position 

 of the triple bond is established by the fact that on oxidation it yields lauric 

 and adipic acids. The structural formula for this acid is CH3(CH2)ioC:- 

 C(CH,)4C00H. 



The best source of tariric acid is the fat of the seeds of Picramnia Sow,^^ 

 a plant indigenous to Guatemala. Vongerichten and Kohler^" have 



81 N. R. Ellis and H. S. Isbell, J. Biol. Chem., 69, 219-238 (1926). 



'2 E. M. Hume, L. C. A. Nunn, I. Smedlev-Maclean, and H. H. Smith, Biochem. J., 

 34, 879-883 (1940). 



83 1. Smedlev-MacLean and L. C. A. Nunn, Biochem. .J., 34, 884-902 (1940). 



8^ O. Turpeinen, J. Nutrition, 15, 351-366 (1938). 



8^ G. O. Bui)', J. B. Brown, J. P. Kass, and W. O. Lundberg, Proc. Soc. Exptl. Biol. 

 Med., 44, 242-244 (1940). 



8'i F. W. Quackenbush, F. A. Kummerow, and H. Steenbock, /. Nutrition, 24, 213- 

 224 (1942). 



87 A. Arnaud, Compt. rend., 114, 79-81 (1892). 



88 A. Arnaud, Bull. soc. chirn. [3], 7, 233-234 (1892). 



89 A. Steger and J. Van Loon, Rec. trav. chini., 52, 593-600 (1933). 

 9" E. Vongerichten and A. Kohler, Ber., 42, 1638-1639 (1909). 



