Microsomal metabolism of N,N-diethyl-m-toluamide (DEET, DET): the extendednetwork of metabolites

1. The aim was to set out to establish the complete network of metabolites arising from the phenobarbital-treated rat liver microsomal oxidation of N, N-diethyl-m-toluamide (DEET). The products formed from DEET and all its sub sequent metabolites were identified by HPLC retention times, UV spectroscop y, mass spectrometry and by comparison with authentic standards. 2. DEET (1a) produces three major metabolites, N-ethyl-m-toluamide (1b), N, N-diethyl-m-(hydroxymethyl)benzamide (2a) and N-ethyl-m-(hydroxymethyl)benz amide (2b), and, at low substrate concentrations or extended reaction times , two minor metabolites, toluamide (1c) and N,N-diethyl-m-formylbenzamide ( 3a). 1b and 2a are primary metabolites and their formation follows Michaeli s-Menten-type kinetics. At low DEET concentrations, ring methyl group oxida tion is favoured; at saturation concentrations, methyl group oxidation and N-deethylation proceed at similar rates. The rate of formation of 2b decrea ses with increasing DEET concentration; 2b is therefore a secondary metabol ite of DEET and DEET acts as a competitive inhibitor of the metabolism of 1 b and 2a. 3. Except for the primary amides, where N-dealkylation is impossible, metab olism of all subsequent compounds, 1b,c, 2a-c, 3a-c and 4a,b, involves an N -deethylation (NEt2 --> NHEt or NHEt --> NH2) competitive with a ring subst ituent oxidation (CH3 --> CH2OH, CH2OH --> CHO or CHO --> CO2H). Surprising ly, the aldehydes 3a-c are also reduced to the corresponding alcohols 2a-c (CHO --> CH2OH); CO inhibits the oxidative metabolism of 3a-c, bur reductio n to 2a-c continues uninhibited. 4. The outcomes of this work are that (1) previously unreported aldehydes 3 b and 3c form part of the DEET network of metabolites, (2) the reduction of the aldehydes 3a-c has the potential to inhibit the formation of the more highly oxidized DEET metabolites, (3) amide hydrolysis was not observed for any substrate acid (4) no evidence was obtained for N-(1-hydroxyethyl)amid e intermediates.