Synthesis and Biological Activities of 4-Trifluoromethylindole-3-acetic Acid : A New Fluorinated Indole Auxin

In our studies on the development of new promoters for the root formation of tree cuttings, 4-trifluoromethylindole-3-acetic acid (4-CF3-IAA), a new fluorinated auxin, was synthesized via 4-trifluoromethylindole and 4-trifluoromethylindole-3-acetonitrile by using 2-methyl-3-nitrobenzotrifluoride as the starting material. As a control compound for comparing biological activities, 4-methylindole-3-acetic acid (4-CH3-IAA) was also synthesized by using 2,3-dimethylnitrobenzene as the starting material. The biological activities of these compounds were compared by three bioassays with those of indole-3-acetic acid and 4-chloroindole-3-acetic acid (4-Cl-IAA), which, like 4-CF3-IAA and 4-CH3-IAA, has a substituent at the 4-position of the indole nucleus. 4-CF3-IAA showed strong root formation-promoting activity with black gram cuttings which was 1.5 times higher than that of 4-(3-indole)butyric acid at 1×10−4 M. 4-CH3-IAA, however, only weakly promoted root formation in spite of its strong inhibition of hypocoty...