Identification of a reactive intermediate of furazolidone formed by swine liver microsomes

Furazolidone (N-(5-nitro-2-furfurylidene)-3-amino-2-oxazolidone) is metabolized by swine liver microsomes under aerobic and anaerobic conditions (rate: 2.55 and 3.25 nmol/mg protein/min, respectively). Covalent binding to microsomal protein amounted aerobically to 0.29 nmol/mg protein/min. Of all amino acids tested, only addition of cysteine to the incubation mixture decreased microsomal protein binding of furazolidone, indicating that covalent binding may occur at protein thiol groups. Two known metabolites of furazolidone, 3-(4-cyano-2-oxobutylidene-amino)-2-oxazolidone and 2,3 dihydro-3-cyano-methyl-2-hydroxyl-5-nitro-1 alpha,2-di(2-oxo-oxazolidin-3-yl) iminomethyl-furo[2,3-b] furan, were minor metabolites. At least 50% of total metabolites is formed by swine liver microsomes via a reductive process of furazolidone as indicated by the formation of a furazolidone-mercaptoethanol conjugate after the addition of mercaptoethanol to the incubation mixture. The conjugate was identified as 3-(4-cyano-3-beta-hydroxyethylmercapto-2-oxobutylidene amino)-2-oxazolidone, indicating that the open-chain acrylonitrile-derivative is the reactive intermediate of furazolidone which also may be responsible for interaction with protein.