Synthesis 



•CH2COOH 



Fluoreneacetic add. 



Early Work on Indole Compounds 



Indole-acetic and -propionic acids bear a close relationship 

 to the tryptophan constituents of proteins. An excellent 

 outline of the earlier researches on the constitution and 

 synthesis of indole-acetic acid and its congeners is given in the 

 article "Tryptophan," by Martha A. Whiteley, in Thorpe's 

 Dictionary of Chemistry (191 6 edition). Tryptophan is 

 3-indole-a-amino-propionic acid. It is somewhat surprising 

 to learn that tryptophan, discussion of which now occupies a 

 prominent place in many textbooks on biochemistry, was 

 discovered so recently as 1901 (Hopkins and Cole), though the 

 name dates from 1890. Skatole is 3-methyl-indole. A sub- 

 stance called skatole-acetic acid was isolated by Nencki in 

 1889. The synthesis of indole-3 -acetic acid was not accom- 

 plished until Ellinger in 1904 performed it to follow up some 

 problems of constitution raised by the work of Nencki and of 

 Hopkins and Cole. Ellinger showed that it was identical with 

 what Nencki had called skatole-carboxylic acid. In 1905 

 Ellinger further showed that the substance called skatole- 

 acetic acid by Nencki was identical with indole-3 -propionic 

 acid. The preparation by Hopkins and Cole (1903) of indole- 

 acetic acid from /-tryptophan by the agency of an anaerobic 

 bacterium has now only a historical interest for chemists, but 

 as it introduces the time factor, it retains an interest for 

 those concerned with the biological production of growth- 

 substances. 



103 



