METABOLITES OF N-ETHYLBENZAMIDE, N,N-DIETHYLBENZAMIDE AND RELATED-COMPOUNDS DETECTED IN RAT URINE BY NMR-SPECTROSCOPY

In rats treated ip with N-ethylbenzamide (EB) at doses of 250-500 mg/k g, this amide was metabolized by hydrolysis to ethylamine and benzoic acid, the latter detected in the urine as hippuric acid. Proposed meta bolic pathways were investigated by treatment of male Wistar rats with EB and N-ethyl-alpha-C-13-benzamide followed by examination of urine samples by high-resolution NMR spectroscopy. Ethylamine was detected b y H-1 and C-13 NMR techniques. Estimation of metabolite levels in 24-h r posttreatment urine by H-1 NMR spectroscopy with an internal standar d of 3-(trimethylsilyl)-1-propanesulfonic acid and correction for back ground levels of hippuric acid in control urine showed that the percen tage of the dose excreted as hippuric acid was 52-75%. The correspondi ng range for the excretion of ethylamine (detected as an ethylammonium cation) was 27-41%. Signals for EB, benzamide, and benzoic acid were not above the background in urine of treated animals. A similar NMR st udy with unlabeled p-chloro-N-ethylbenzamide (p-Cl EB) resulted in the detection of p-chlorohippuric acid and ethylamine. Treatment of rats with N,N-diethylbenzamide and p-chloro-N,N-diethylbenzamide gave the s ame detectable metabolites in the urine as those found in experiments with EB and p-CI EB. These observations could be rationalized with a m etabolic pathway involving an initial oxidative mono-N-deethylation re action followed by enzymatic hydrolysis of the secondary amides to eth ylamine and benzoic acids and conjugation of the latter with glycine. N-Methylbenzamide was also found to be eliminated in the urine as hipp uric acid.