Synthesis 



common among protein derivatives — ^the a-amino acids; 

 this suggests an explanation of the values of indole-pyruvic 

 acid as a substitution for tryptophan. 



The immediate chemical interest of Jackson's 1929 paper 

 lies in its preliminary description of new or improved methods 

 of preparation of several indole compounds, amongst them the 

 following: indole-3 -butyric acid from application of the 

 Fischer ring-closure to the phenylhydrazone of ethyl 

 hydrogen a-ketopimelate (full details of this synthesis were 

 published by Jackson and Manske (1930) ); indole-3- 

 propionic acid was prepared according to Kalb, Schweizer, 

 and Schimpf (1926) ; indole-3-pyruvic acid was prepared 

 by the method of Granacher, Gero, and Schelling (1924). 



Berg, Rose and Marvel (1929-30), who also were interested 

 in the animal metabolism of tryptophan, reported the prepara- 

 tion of indole-3 -propionic acid from adipic acid. Diethyl 

 adipate was prepared and condensed with itself (van Ryssel- 

 berge, 1926) to give ethyl r^c/opentanone-2-carboxylate. 

 Indole-3 -propionic ^^id was then formed by the procedure of 

 Kalb, Schweizer, and Schimpf (1926) as modified by Manske 

 and Robinson (1927). 



The same authors prepared indole-3 -pyruvic ^cid by apply- 

 ing the Grignard reaction to indole to give indole-aldehyde 

 (Putochin's (1926) modification of the method of Majima and 

 Kotake (1922): the method was further modified by Berg 

 et al. in that di-«-butyl ether was used as a solvent). The 

 aldehyde was converted to the pyruvic acid according to the 

 procedure of Ellinger and Matsuoka (1920). 



Recent Indole-Acetic Acid Syntheses 



Two syntheses of indole-3 -acetic acid and one synthesis 

 each of indylene-i : 3-diacetic acid and of two other indole 

 acids, were reported by Jackson and Manske (1935). One of 

 the indole-acetic acid syntheses was from diethyl-^-cyano- 



H2O HCl 



propionacetal — >- acid — ►- semi-aldehyde of succinic acid 

 ( +H2O); this, without isolation, was condensed with phenyl- 

 hydrazine; the product was subjected to the Fischer indole 



105 



