4-Chloro-3-indoleacetic acid

Organohalogens also serve as hormones. Vegetables such as lentils, beans, and peas synthesize the growth hormone 4-chloro-3-indoleacetic acid. A cockroach produces two chlorine-containing steroids as aggregation pheromones. Female ticks use 2,6-dichlorophenol as a sex attractant. Thyroid hormones (see Figure 1) contain iodine, and an organobromine is involved in the mammalian sleep phenomenon. 

Other well-known indoles that have various natural sources are skatole (3-methylindole) (2), serotonin (3), L-tryptophan (4), tryptamine (5), the plant growth hormones 3-indoleacetic acid (6) and 4-chloro-3-indoleacetic acid (7) [19], the mushroom hallucinogen psilocin (8), and the indole-derived ancient dyes indigo (9) [20] and Tyrian Purple (10) [19] (Scheme 1). 

Audus and Quastel (4) have found that the presence of p-aminobenzoic acid exerts an antagonism, though a relatively feeble one, to the root growth inhibitory actions of 2,4-dichlorophenoxyacetic acid, 2-chloro-4-methylphenoxyacetic acid, 2-naphthoxyacetic acid, and 2-indoleacetic acid. For any marked degree of antagonism the concentration ratio of p-aminobenzoic acid to the growth substance must be of the order of 10,000. This relatively feeble action is ii marked contrast to the effect of p-aminobenzoic acid on the... 

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