Inhibitory Activities of Rhodanine Derivatives on Plant Growth

Rhodanine (1), rhodanine-3-acetic acid (2), methylrhodanine (3), and aminorhodanine (4) inhibited the growth of plants. Among them, 4 was the strongest inhibitor of the roots of all the tested plants. On the other hand, N-acetylaminorhodanine (5) and N-benzoylaminorhodanine (6) greatly decreased the inhibitory activity. The results suggest that the free amino group at N-3 of 4 is essential to the greater inhibitory activity of rhodanine derivatives. The plant-growth inhibition of 1–6 is related to the chlorophyll content of the plant treated with them and their acute toxicities in mice.