Phytotoxicity of Perlatolic Acid and Derivatives

Abstract

Perlatolic acid (1), methyl perlatolate (2), and the products of perlatolic acid alcoholysis —namely, methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, and n-hexyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (3-11)—were evaluated for their herbicidal potential on Lactuca sativa L. (lettuce) and Allium cepa L. (onion) seeds. The compounds exhibited low phytotoxicity on L. sativa germination. Perlatolic acid (1) proved the most active compound (20%). Activity was lowest for n-hexyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (11) (3.5%). The esters iso-propyl and sec-butyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (6 and 8, respectively) inhibited root (35% e 43%, respectively) and hypocotyl growth (59% e 56%, respectively). The esters n-butyl, n-pentyl, and n-hexyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (7, 10, and 11, respectively) proved phytotoxic to A. cepa, delaying and reducing seed germination (27%), while n-pentyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (10) was the most inhibitory for root (42%) and coleoptile growth (24%). The behaviors of iso-propyl, sec-butyl, and n-pentyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (6, 8, and 10, respectively) suggest the potential utility of these esters as natural herbicides. The esters iso-propyl and sec-butyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (6 and 8, respectively) may serve as model molecules in the investigation of potential herbicides for dicotyledon control, while n-pentyl 2-hydroxy-4-methoxy-6-n-pentylbenzoate (10) may serve the same function for monocotyledon species.