Chemical structure and biological activity 



These were placed in water and a biological assay was carried out using 

 either wheat coleoptile sections or split pea stem segments. Authentic 

 compounds were run for comparison in all experiments. 



o)- (2 : A-dichlorophenoxy) alkanecarboxylic acids 



Whether pretreated with wheat or with pea tissue, assessment of the 

 chromatogram segments in both the wheat and pea tests revealed the 

 formation of 2:4-dichlorophenoxyacetic acid (2:4-D) (i?^ 0-35-0-45) from 

 the butyric and caproic acids (n = 3 and 5), but not from the propionic, 

 valeric, and heptanoic acids (ra = 2, 4, and 6). These results are readily 

 explicable on the basis of /^-oxidation. 



CO- (2 : A-dichlorophenoxy) alkanecarbonamides 



The chromatograms obtained from the first, third, and fifth members of 

 the series {n ^ 1, 3, 5) pretreated with wheat or pea tissue showed two 

 peaks of activity both with the wheat and the pea bio-assay methods. The 

 first of these peaks (/?^ 0-35-0-45) represented 2:4-D, and the second, 

 residual amide (i?^ 0-75-0-85), present as such on the paper but presumably 

 converted to 2:4-D in the bio-assay. Since other homologues {n = 2, 4, 6) 

 yielded no 2:4-D in these experiments, the results indicate strongly that 

 amide to acid hydrolysis can occur in both the wheat and pea tissues and 

 that the acid produced then undergoes /j-oxidation. 



CO- (2 : A-dichlorophenoxy) alkanenitriles 



When these compounds were pretreated with pea tissue, only the first 

 member (w = 1) yielded 2:4-D. Two peaks of activity were revealed on this 

 chromatogram when both the wheat and pea tests were used for bio-assay 

 and these peaks corresponded with the R^ values of 2:4-D {R^ 0-35-0-45) and 

 2:4-dichlorophenoxyacetonitrile (/?^ 0-8-0-9). With other members of the 

 series, the chromatograms assayed in the pea test showed uniform inactivity 

 over the whole paper, thus confirming that hydrolysis of these higher nitriles 

 to the acids cannot occur in pea tissue. As already noted, all the nitriles 

 showed activity in the wheat test {Figure 2). The chromatographic and wheat 

 cylinder bio-assay investigations of nitrile solutions pretreated with wheat 

 tissue showed that all members of the series yielded 2:4-D in amounts which 

 are related to their activity in the wheat cylinder test. In all these chromato- 

 grams there was also a second peak of activity representing residual nitrile 

 (i?^0-8-0-9). With a pea test bio-assay, however, these chromatograms 

 showed no second peak of activity in the higher R^ regions since the higher 

 nitriles are inactive in the pea test. 



The methods employed in this work, then, provide a means whereby the 

 growth-regulating activity of compounds can be related to their conversion 

 to known active auxins within the tissues of the biological material employed. 

 It is significant that in all cases where activity is shown the active acetic acid 

 (2:4-D) is produced (cf. Seeley et al., 1956). 



One of the most interesting features of this work is the activity of all the 

 nitriles in the wheat cylinder test {Figure 2). The greatest activity is again 

 shown by the acetic, butyric, and caproic derivatives {n = \, 3, 5) and 

 this is explicable on the basis of hydrolysis of — CN-> — COOH followed by 



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