THE RESOLUTION OF PHYTO-HORMONE ACIDS BY 



MEANS OF THEIR OPTICALLY ACTIVE 



PHENYL/^OPROPYLAMIDES. 



RESOLUTION OF a-(l-NAPHTHYL)PROPIONIC ACIDt 



J. M. F, Leaper and J. R. Bishop 

 American Chemical Paint Company, Ambler, Pa. 



HISTORY OF THE RESOLUTION OF PHYTO-HORMONE ACIDS 



The term 'hormone acids' will be used here to include two main groups: 



(a) Acids actually derived from plant sources, or closely related chemically 

 to these; e.g. indole-3-acetic acid, a-(indole-3)propionic acid, and 

 a-(indole-3)«-butyric acid. 



(b) Acids not related to these and arising solely from synthetic sources, 

 e.g. the substituted and unsubstituted phenoxy- and naphthoxyacetic acids 

 and homologues and their related imino and thio derivatives. Also in this 

 category will be the a- and /:?- naphthylacetic acids and their homologues. 



Some of both these classes have an asymmetric carbon atom and are 

 capable of being resolved into their optically active enantiomorphs. 



It was fairly obvious from the start and in fact might be considered axio- 

 matic that when such resolutions were brought about, the resulting two 

 isomers would produce different physiological responses in the appropriate 

 plant tissue. I say appropriate advisedly since some plant response can often 

 be found that does not differentiate between the two isomers, e.g. the 

 variations observed by Kogl (1944) in the pea test and the Avena test 

 using indole-a-propionic acid isomers. However, these are comparatively 

 rare exceptions. 



As has often been pointed out, the parallel cases in animal physiology 

 involving the optical isomers of such compounds, both naturally occurring and 

 synthetic, as thyroxine, hyocyamine, adrenaline, ascorbic acid, amphetamine, 

 and many others, where very striking differences in biological reactions are found 

 as between the isomers, would seem to make it obvious that similar differenti- 

 ations would be the case with compounds having phytobiological activity. 



Actually, the first resolution of what we are calling 'hormone acids' was 

 made as far back as 1925 by Fourneau and his co-workers (Fourneau and 

 Balaceano, 1925) at the Pasteur Institute, who resolved a-(2-naphthoxy)- 

 propionic acid. However, this was many years before the phytobiological 

 activity of 2-naphthoxyacetic acid was disclosed by Irvine (1938) and the 

 relative activity of the isomers of a-(2-naphthoxy)propionic acids studied by 

 Smith and Wain (1951). Fourneau was primarily interested in producing 

 a cheap and readily available optically active acid for use in resolving 

 synthetic adrenaline and related vasoconstrictors. 



It is worthy of note that whereas most of the useful medicinal compounds 

 found naturally are optically active, the only well-defined phyto-hormone 



■fThis paper was read at the Conference by J. M. F. Leaper. 



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