Abstract
Isothymol, thymol and eugenol in the essential oil of Alpinia speciosa possess strong antifungal activity against plant pathogenic fungi. Although these active constituents are volatile in the natural environment, they can be changed into nonvolatile phosphorothionates by reaction with thiophosphoric agents using triethylamine or aq. NaOH as a base. Twenty-eight kinds of thiophosphorus esters were synthesized. During volatile testing, phenethyl alcohol and isothymol were almost volatilized in 9 and 14 days, respectively and eugenol was volatilized 89.2% in 14 days. Dimethyl isothymyl phosphorothionate (17), dimethyl eugenyl phosphorothionate (19), dimethyl phenethyl phosphorothionate (20), and diethyl phenethyl phosphorothionate (25) derived from each essential oil were scarcely volatilized and the volatility of 17, 19, 20, and 25 were 4.0, 2.3, 12.6, and 7.6% in 14 days, respectively. Among the synthesized compounds, 20 showed the strongest antifungal activity, 39.6 and 56.6% inhibition at 10ppm against Pythium sp. and Corticium rolfsii, respectively. Compound 20 had activity as potent as Iprobenfos.
