The thirty-four N-methyl-2)-methoxy(substituted)benzanilides were synthesized and their preventive activities against rice blast were studied by the pot test. The substitution at the para-position of benzoyl moiety varied the activity to various extents.The inhibitory activity of N-methyl-2)-methoxy-4-substituted benzanilides on the penetration of infection pegs from appressoria of Pyricularia oryzae were also measured by using cellophane film as a model of plant cell walls and the structure-activity relationships were analyzed using the physicochemical parameters and regression analysis. The inhibitory activities were related to the bulkiness and electronic effect of the substituents and parabolically to the hydrophobicity of the molecules.
A few synthetic methods of N-substituted-carbamimidoylformic acid (6) were examined. Among them, condensation of ethyl 1-carbethoxyformimidate or ethyl thiooxamidate with amines and followed by partial hydrolysis gave unsuccessful results, except of the case of benzylamine in the latter reaction. Direct substitution of potassium thiooxamidate (9) with alkylamines in water gave 6, potassium and/or alkylammonium N-substitutedthiooxamidate in fairly good yield, depending on conditions used. The presence of heavy metal ions in the reaction system caused an extensive decomposition of 9, however, the substitution proceeded smoothly by treatment of alkyl- and aryl-ammonium N-unsubstituted- or N-substituted-thiooxamidate in methanol with mercuric oxide or lead oxide to give in a good yield 6 or N,N-disubstituted-carbamimidoylformic acid, respectively.
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