F. G. TEUBNER^ 

 S. H. WITTWER 

 JANE Y. SHEN- 



Michigan State University 



Relationship of Molecular Structure to 



Biological Activity In the 

 H-Arylphthalatnlc Adds' 



The activity of a number of substituted iV-phenylphthalamic acids in 

 stimulating fruit set of tomato was reported by Hoffmann and Smith 

 in 1949 (8). Since then, these chemicals have received only infrequent 

 attention as fruit setting agents (3), although the closely related iV-1- 

 naphthylphthalamic acid has shown considerable promise as a se- 

 lective herbicide (4). The action of iV-m-tolylphthalamic acid in caus- 

 ing increased flower formation in the tomato (23) has led to the prac- 

 tical use of this chemical to obtain increased flower and fruit num- 

 bers and, thereby, higher yields of greenhouse grown tomatoes (33). 

 It was subsequently found that a number of the chloro- and methyl- 

 substituted iV-phenylphthalamic acids possessed flower forming activ- 

 ity and that the structural requirements of these compounds for alter- 

 ing flower formation apparently differed from those for auxin ac- 

 tivity in the substituted benzoic and phenoxyacetic acids (24). 



At present, only two other synthetic growth regulators, a-(2- 

 naphthoxy)phenylacetic acid (17) and the 2,3,5-triiodobenzoic acid 

 (6, 31, 34, 35), have been clearly demonstrated to increase flower forma- 

 tion in the tomato. Although 2,3,5-triiodobenzoic acid has been con- 

 sidered an auxin antagonist (5), or auxin synergist (26), it also has 

 auxin properties (1, 13). Similarly, a-(2-naphthoxy)phenylacetic acid 

 is highly active in stimulating parthenocarpic fruit set (18) but has not, 

 to our knowledge, been evaluated for auxin activity in any of the more 

 classical assays. This report deals with the molecular structure of the 



1 Subsequently: Department of Horticulture, University of Nebraska, Lincoln, 



= Subsequently: Division of Biological and Medical Research, Argonne National 

 Laboratory, Lemont, Illinois. 



^Journal article No. 2485 from the Michigan Agricultural Experiment Station. 



[259] 



