Why Does m-Methyl Substituted Pesticides Show Higher Insecticidal Activity? On the Phenyl N-methylcarbamate and m-xylyl-N-methylcarbamate Derivatives

왜 m-methyl 치환 살충제들은 강한 살충작용을 나타낼까? -Phenyl N-methylcarbamate와 m-xylyl-N-methylcarbamate 유도체들에 관하여-

In order to seek the molecular basis of higher insecticidal activity of the carbamates with two methyl groups, m-xylyl-N-methylcarbamate(MXNMC) than the corresponding unsubstituted phenyl N-methylcarbamate(PNMC), these two derivatives have been studied by molecular orbital(MO) theoretically using extended $H\ddot{u}ckel$ theory(EHT), and analysis of regression and linear free energy relationship(LFER). The most stable stereo structure(Z, Z) shows that the phenyl group occupies vertical(${\theta}=90^{\circ}$) position on the plane of the N-methylcarbamyl group. Regression analysis shows that especially good correlation exists between the $pI_{50}$ values and the calculated MO quantities when the hydrogen atomic charge of metaposition and of m-methyl groups, and LUMO energy are taken as variables. The LFER analysis on the carbamylation indicates that field(F) effect(60%) is slightly larger than resonance(R) effect(40%) in PNMC(E>R), whereas, in case of MXNMC, R effect(98.6%) is much larger than F effect(1.4%)($R{\gg}F$). From the basis on the findings, the enhancement of insecticidal activity of MXNMC may be the result of hyperconjugation by m-methyl groups.

2개의 m-methyl group이 치환된 m-xylyl N-methylcarbamates(MXNMC)가 비치환된 phenyl N-methylcarbamates(PNMC)보다 높은 살충작용을 나타내는 이유를 알아보기 위하여 이들 두 유도체들이 확장 $H\ddot{u}ckel$(EHT) 이론에 따른 분자궤도(MO) 이론과 회귀 및 자유에너지 관계(LFER) 분석에 의하여 연구되었다. 가장 안정한 입체구조는 phenyl group이 N-methylcarbamyl group의 면에 대하여 수직(${\theta}=90^{\circ}$)인 형태(Z,Z)이었으며, 회귀분석은 $pI_{50}$ 상수들과 meta-위치 및 m-methyl group의 수소원자 하전과 LUMO에너지의 계산된 MO량을 변수로 취했을 경우가 가장 좋은 상관관계를 나타내었다. Carbamylation 반응에 관한 LFER분석 결과, PNMC에서는 공명(R)-효과(40%)보다 장 (F) 효과(60%)가 약간 컸으나(F>R), MXNMC의 경우에는 R-효과(98.6%)가 F-효과(1.4%)보다 월등히 큰 값($R{\gg}F$)을 보였다. 이와 같은 사실로부터 MXNMC의 살충작용이 증진되는 것은 m-dimethyl group에 의한 hyperconjugation의 결과라고 믿어진다.