CLASSIFICATION AND STRUCTURE OF FATTY ACIDS 37 



acid chains under such conditions have an odd nimiher of carbons. The 

 Cio to C28 members of this series were isolated. As a result of a study of 

 the x-ray diffraction patterns of a series of these acids (12-methyltride- 

 canoic, 14-methylpentadecanoic, IG-methylheptadecanoic, 18-methyl- 

 nonadecanoic, 20-methylheneicosanoic, and 22-methyltricosanic acids) 

 N'elick^^" clearly demonstrated homology in the series. The long crystal 

 spacings were shown to increase linearly with the carbon content. 



The second of the series of homologous acids, the so-called anleiso series, 

 consists of members with an odd number of carbon atoms containing a 

 single methyl side chain attached to the antepenultimate (second from the 

 last) carbon atom. In this case the fatty acid chains are composed of an 

 even number of carbon atoms. The C9 to C31 members in this series were 

 isolated by Weitkamp.^ ^'elick and English^ ^' succeeded in synthesizing 

 rf-14-methylpalmitic acid, CH3CH2CH(CH3)(CH2)i2COOH, which was 

 shown to be identical with the natural product from wool wax. It is there- 

 fore believed that the anteiso series consists of the rf-isomers of even- 

 chained acids with a single methyl group in the antepenultimate position. 

 On the basis of x-ray diffraction studies, the series was shown to be homol- 

 ogous. ^^^ 



{8) Cyclic Acids 



Interest in the cyclic fatty acids has been stimulated by the report of their 

 use in the treatment of leprosy. Several such cyclic acids are present in the 

 seed oils of tropical plants of the family Flacourtiaceac, and especially of the 

 genus Hijdnocarpus. The principal sources are chaulmoogra oil, lukrabo 

 oil, and gorli seed oil. The best known cyclic fatty acids are chaulmoog- 

 ric, C18H.S2O2, hydnocarpic, C16H28O2, and gorlic, C18H30O2. AH of these 

 acids have a terminal cyclopentenyl ring, and they vary from each other 

 only in the nature of the side chain. 



Although it has been recognized for many years that such oils are specific 

 for the treatment of leprosy, no satisfactory method of biological testing 

 has been available until recently. It has been shown^^- that the thera- 

 peutic activity can be judged by the bactericidal action upon the leprosy 

 bacillus, B. leprae. Such an in vitro test has been widely employed by the 

 Adams group in testing the structural requirements for activity in a 

 number of naturally occurring and synthetic acids. 



a. Chaulmoogric Acid. Although the specific action of chaulmoogra 

 oil (Gynocardia odoraia) upon leprosy was known to the Chinese, the 

 nature of the fatty acids present in this oil was not understood until the 



'«> S. F. Velick, J. Am. Chem. Soc, 69, 2317-2322 (1947). 



'«' S. F. Velick and J. Enp;lis]i, Jr., J. Biol. Chem., 16^, 473-480 (1945). 



1" E. L. Walker and M. A. .Sweeney, J. Injeclious Diseases, 26, 238-264 (1920). 



