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-CF(3)-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-CH(3)-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-CF(3)-IAA and 4-CH(3)-IAA, has a substituent at the 4-position of the indole nucleus. 4-CF(3)-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 1x10(-4) M. 4-CH(3)-IAA, however, only weakly promoted root formation in spite of its strong inhibition of hypocotyl growth in Chinese cabbage and promotion of hypocotyl swelling and lateral root formation in black gram. On the other hand, 4-CF(3)-IAA demonstrated weaker activities than 4-CH(3)-IAA and 4-Cl-IAA in these two bioassays.