Plant Qroivth'Suhstances 



First Syntheses 



Emil Fischer's method of ring-closure was used by Ellinger 

 (1904) for the first synthesis of indole-3-acetic acid. The 

 phenylhydrazone of methyl aldehydo-propionic acid, on 

 heating with zinc chloride, or, better, by prolonged heating 

 with alcoholic sulphuric acid (Wislicenus), yielded methyl 

 indole-3-acetate. The aldehydo-propionic acid was prepared 



HC=C.COOH 

 in fair yield by boiling aconic acid | | with water. 



O.CO.CH2 

 The aconic acid was prepared from commercial itaconic acid ; 

 for details and references, the original should be consulted. 

 In his next paper, Ellinger (1905) described a preparation of 

 the now usual indole-propionic ([3-3-indole-propionic) acid by 

 a tedious and probably uncommercial process, having 

 y-aldehydobutyric acid as intermediate. In the same paper 

 Ellinger also described a similar preparation from aldehydo- 

 wo-butyric acid of the compound isomeric in the side-chain 

 (a-3 -indole-propionic acid), for which he used the strange- 

 sounding name indole-methylacetic acid.^ 



Relation to Animal Physiology 



It is of interest that several of the more recent preparations 

 of indole acids — some of which are now known to have remark- 

 able effects upon the growth of plant organs — had their 

 genesis in a study of the role of tryptophan in animal diets. 

 Jackson (1929) devised a diet deficient in tryptophan, in 

 substitution for which various indole compounds were tried. 

 Indole-pyruvic acid was the only one of these compounds cap- 

 able of replacing tryptophan in rats' diet ; it caused resumption 

 of growth in animals deprived of tryptophan. A mixture of 

 pyruvic acid and ammonium pyruvate leads to the formation 

 (de Jong, 1900, 1904) of the type of amino acids most 



^ The name is correct provided that the methyl group has not wandered 

 into either ring. It suggests an interesting chemical catch. Q. What is 

 methyl-acetic acid ? Ans. Propionic acid. Q. Is, then, indole-methyl-acetic 

 acid identical (for any one point of substitution in the indole nucleus) with 

 indole-propionic acid? — Try it on your friends! 



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