Effect of esterification and side-chain alkylation on alteration of translocation characteristics of methamidophos.

1. The phloem mobility and systemic activity of methamidophos (I); propanedioic acid 1-phosphoramidothionic acid O,S-dimethyl ester, 2-methyl, 3-0monoethyl ester (II); propanedioic acid, 1-phosphoramidothionic acid O,S-dimethyl ester, 2,2-dimethyl, 3-monoethyl ester (III); and butenoic acid, 1-monoethyl ester, 2,3,-E & Z, 3-phosphoramidothionic acid O,S-dimethyl ester (IV) were investigated in soybeans (Glycine max L.) with a bioassay using cabbage looper (Tricoplusia ni Hüber) larvae to determine the impact of side-chain alkylation on the translocation of propanedioic acid 1-phosphoramidothionic acid O,S-dimethyl ester 3-monoethyl ester (V). 2. The ethyl ester of ethanedioic acid, 1-phosphoramidothionic acid OS,-dimethyl ester 2-monoethyl ester (VI) was compared with a bukly ester analogue, the 2-(methyl)butyl ester (VII). 3. Monoethylation of the alpha-carbon of II resulted in enhanced insecticidal and systemic activity, which was interpreted as a steric hindrance to fatty acid oxidation of the propanedioic moiety of III, but not of II and V. 4. Compound IV was an effective insecticide by topical and feeding response, but was not a systemic. 5. A large bulky ester (VII) blocked deesterification and the systemic insecticidal response was lost when compared with VI. 6. This study suggests that the utilization of the malonate semialdehyde-pathway enzymes found in plants but not in insects may be fruitful in the molecular design of new insecticides.