Synthesis and antifungal activity of 2-allylphenol derivatives against fungal plant pathogens

Abstract 2-Allylphenol (2-AP) is an effective fungicide against a number of plant pathogens, which can be metabolized and bio-transformed to four chemical compounds by Rhizoctonia cerealis . To determine if its degradation affects antifungal activity, two major metabolites derived from 2-AP including 2-(2-hydroxypropyl) phenol and 2-(3-hydroxypropyl) phenol were synthesized. Inhibition of mycelial growth of several plant pathogens by the metabolites was evaluated, and structures of two metabolites were determined by hydrogen nuclear magnetic resonance ( 1 H NMR). Among these metabolites, only 2-(2-hydroxypropyl) phenol inhibited test pathogens effectively. EC 50 values of 2-(2-hydroxypropyl) phenol for inhibition of mycelial growth of R. cerealis , Pythium aphanidermatum , Valsa mali and Botrytis cinerea ranged from 1.0 to 23.5 μg/ml, which were lower than the parental fungicide 2-AP that ranged from 8.2 to 48.8 μg/ml. Hyphae of R. cerealis and P. aphanidermatum treated with 2-(2-hydroxypropyl) phenol were twisted. Newly developed hyphae were slender, twisted and swollen on the tip, while old hyphae were hollow and ruptured. This is the first report indicating the formation of 2-(2-hydroxypropyl) phenol may have contributed to toxicity of 2-allylphenol in control of plant pathogens.