Degradation within plant tissues 



/5-oxidation to yield 2:4-D. The production of 2:4-D from the propionic, 

 valeric, and heptanoic nitriles {n ■= 2, 4, 6), however, is not explicable by 

 this two-stage reaction mechanism. At the same time, there is no reason to 

 suppose that in wheat tissue these three compounds are not subject to 

 hydrolysis followed by /3-oxidation, which in their case would lead to 2:4- 

 dichlorophenol as the end product. On the other hand, evidence of their 

 conversion to 2:4-D in wheat tissue indicates that some other type of break- 

 down must also be involved. To produce 2:4-D from the valeronitrile, 

 for example, it is clear that a single carbon atom must have been lost from 

 the side chain at some stage. This may occur as follows : 



OCH„CH,CR,CH„ 



CI 



CN OCH„CH,CHX;OOH OCHoCOOH 



CI 



/3-oxiclation 



> 



CI 



CI 



CI 



(valeronitrile) 

 « = 4 



CI 



2:4-D 



Now there is already evidence that the — CH2CN grouping can be degraded 

 to carboxyl in the animal body. Thus, for example, /?-chlorobenzylnitrile 

 fed to dogs is excreted in the urine as a derivative of /?-chlorobenzoic 

 acid (Adeline et al., 1926). Further evidence of the loss of a one- carbon 

 fragment from the — CHgCN grouping arises from the work of Pattison 

 (1953) in his studies on the toxicity of co-fluoroalkanenitriles to rats. 

 A similar biochemical degradation would explain our results with oj-(2:4- 

 dichlorophenoxy)alkanenitriles in wheat coleoptile tissue. 



In this connection, it is of considerable interest that a separate investiga- 

 tion which was proceeding here with indole compounds has provided strong 

 confirmatory evidence that nitriles can be so degraded in plant tissue with the 

 loss of one carbon atom. In this work, which is referred to in one of our 

 other contributions to this Conference (Seeley et al., 1956), indole-3-aceto- 

 nitrile has been shown to be converted to indole-3-carboxylic acid in presence 

 of wheat coleoptile or pea stem tissues, i.e. 



\/\NH 



-CH2CN 



/ 



\/\NH/ 



COOH 



This clearly provides another example of the type of nitrile degradation 

 which we suggest occurs in the phenoxy nitriles. Since, in this breakdown, 

 the a-methylene grouping becomes oxidized, the process may be conveniently 

 referred to as a-oxidation of nitriles. 



Finally, since we have shown that pea tissue can convert indole-3-aceto- 

 nitrile to indole-3-carboxylic acid, and since there is evidence of the presence 

 in germinating peas of a compound with properties similar to that of 

 indole-3-acetonitrile (Cartwright et al., 1956), it was logical to look for the 

 carboxylic acid as a natural constituent of this tissue. Dr. Cartwright has in 

 fact found this acid to occur in young pea plants (Cartwright et al., 1956). 



193 



