METABOLISM OF FLUMETSULAM (DE-498) IN WHEAT, CORN, AND BARLEY

Flumetsulam (N-[2,6-difluorophenyl]-5-methyl(1,2,4)-triazolo[1,5-a]pyrimidine-2-sulfonamide) was metabolized by similar hydroxylation and glucose conjugation pathways in tolerant corn, wheat, and barley seedlings. Two primary monohydroxylated metabolites, N-[2,6-difluoro-4-hydroxyphenyl]-5-methyl(1,2,4)-triazolo[1,5-a]pyrimidine-2-sulfonamide (M 1) and N-[2,6-difluorophenyl]-5-hydroxymethyl(1,2,4)-triazolo[1,5-a]pyrimidine-2-sulfonamide (M 2) and a dihydroxylated metabolite N-[2,6-difluoro-4-hydroxyphenyl]-5-hydroxymethyl(1,2,4)-triazolo[1,5-a]pyrimidine-2-sulfonamide (M 3) were isolated and identified by negative FAB/MS and proton NMR spectroscopy. Isolated secondary O-glucosides of metabolites M 1, M 2 and M 3 were tentatively identified by negative FAB/MS and/or β-glucosidase hydrolysis. Microsomal cytochrome P450-dependent monooxygenases responsible for flumetsulam hydroxylation were isolated from naphthalic anhydride- and ethanol-induced shoot tissues of etiolated corn, wheat, and barley seedlings. Enzyme activity required NADPH and molecular oxygen and was inhibited by carbon monoxide in the dark and by other cytochrome P450 inhibitors. Inhibition by carbon monoxide was reversed by light. Enzyme kinetic and inhibition studies suggested that different cytochrome P450 forms may be involved in flumetsulam hydroxylation at the 4-position on the 2,6-difluorophenyl ring (M 1) and the methyl group on the substituted pyrimidine moiety (M 2). © 1993 Academic Press.