Plant Qrowth'Suhstances 



Ehrlich's original method of preparation of indole-ethyl 

 alcohol involved the use of tryptophan (which is expensive) 

 and a large excess of sugar. Ethyl alcohol can be employed as 

 source of energy for the yeast, the purification of the desired 

 product being thereby made more easy than when sugar is 

 used. Ehrlich {loc. cit., p. 889) gave details of the preparation 

 of indole-ethyl alcohol from tryptophan and ethyl alcohol in 

 presence of a yeast. The requisite amount of alcohol is much 

 smaller than the massive dose of sugar required for the sugar 

 preparation. 



It is not clear whether the ability to deaminize tryptophan 

 in laboratory culture is peculiar to strains of yeast similar 

 to those used by Ehrlich. The biological method, however, 

 appears to have interesting possibilities and is probably sus- 

 ceptible of further refinement. It might be worth while to 

 explore the potentialities of the microbiological deamination 

 of casein or of its crude products of hydrolysis, the latter 

 being obtained by either chemical or biological means. See 

 also p. 103. 



A substance probably identical with 3-indole-acetic acid 

 has been formed in minute amounts by the action of legume 

 nodule bacteria on tryptophan (Link et al. (1937) ; Chen 

 (1938); Georgi and Beguin (1939) ); it may help to account 

 for the auximonic effect of leguminous nodules observed by 

 Bottomley (191 5- 17, E). 



Higher Indole-Acids 



Details of a synthesis of 3-indolyl-propionic acid from 

 CO w-diethoxy-propyl diethyl-malonate (from ^-chlorpro- 

 pionacetal and sodium diethyl malonic ester ) are given by 

 Davies, Atkins, and Hudson (1937). The acid prepared in 

 this way is free from the lower homologue. 



Manske and Leitch (1936) have described in considerable 

 detail the syntheses of 8-(3-indolyl)-valeric acid and the 

 related 6^-alkyl-p-(5-methyl-indolyl) -propionic acid. Both 

 these have been shown to possess the plant-physiological 

 properties of a growth-regulating substance. 



The indole-valeric acid was synthetized by the application 



108 



