ALACHLOR AND ITS ANALOGS AS METABOLIC PROGENITORS OF FORMALDEHYDE - FATE OF N-METHOXYMETHYL AND OTHER N-ALKOXYALKYL SUBSTITUENTS

Alachlor, metolachlor, butachlor, and several analogues yield 20-60 mol% formaldehyde on incubation with the mouse liver microsomal mixed-function oxidase system under standard conditions. Studies with N-CD2- and N-13CH2-labeled alachlor established that 70-80% of the metabolically generated formaldehyde is from the N-methylene group. The remainder is from the O-methyl group, a result confirmed by parallel studies with [O-13CH3]alachlor. In mechanistic terms this implies that the spontaneous decomposition of the side chain following O-CH3 hydroxylation accounts for only about half of the total formaldehyde liberated from alachlor and therefore the remainder must arise via an alternative process. This need to invoke a mechanism other than O-CH3 hydroxylation is supported by the observation that the O-tert-butyl and O-phenyl analogues of alachlor are also metabolic progenitors of formaldehyde. One plausible mechanism involves one-electron oxidation at nitrogen followed by loss of methoxy radical to form the methylene iminium ion and ultimately the N-hydroxymethyl derivative. The latter compound is a formaldehyde progenitor with a half-life of approximately 8 min in pH 7.4 aqueous solution at 18-degrees-C.