Abstract
The well-established herbicide, asulam (methy14-aminobenzenesulphonylcarbamate; M&B 9057) is used widely for control of weed species including docks and bracken. The compound resembles sulphonamides in structure. Most of an oral dose of asulam is eliminated from rats mainly in the urine (75%) and faeces (19%) within 24 hours. Biotransformation in the intact animal is similar to the N-acetylation of some sulphonamides. The major metabolite is N4-acetylasulam which is excreted rapidly in the urine (15% male; 9% female) and also appears in faeces (4%). Induction of rats with asulam does not effect overall metabolism and excretion except that decarbamoylation is increased in the gut. N4-acetylsulphanilamide is also produced ( 2%) by decarbamoylation in the gut. N4-acetylasulam formation in vitro is located in the cell-membrane fraction of liver. Asulam is not eliminated in the bile (1% dose) in vivo. No binding spectrum is obtained with microsomal cytochrome P450. Continuous perfusion through liver for 6 hours does not increase biliary elimination, but at least three water-soluble unidentified compounds (4.5%) are formed in plasma. In contrast to the in vivo state asulam causes rapid oxygen uptake in vitro with microsomes producing an isolatable colored metabolite (max = 330 nm) which contains ring-substituted hydroxy sulphonamido and nitrogen substituted carbamate groups. Mass spectrometry shows this not to be 2-hydroxyasulam.