APPARENT INTRAMOLECULAR ACYL MIGRATION AND HYDROLYSIS OF FUROSEMIDE GLUCURONIDE IN AQUEOUS-SOLUTION

The stability of furosemide glucuronide (FG) was investigated in buffe r solutions ranging from pH 1 through 10. This glucuronic acid conjuga te was the major metabolite of furosemide (F) excreted in human urine. FG, obtained by extraction from human urine, was purified by ion-exch ange chromatography. The concentration of FG, acyl migration isomers o f FG (FG-iso), and F were determined simultaneously with an HPLC metho d that included fluorescence detection and gradient elution. FG was fo und to be unstable in highly acidic and in neutral to alkaline solutio ns. Hydrogen ion and hydroxy ion catalyzed the hydrolysis of FG below pH 2.8 and above pH 5.6, respectively. Above pH 3.7, FG instability le d to the formation of eight FG-iso compounds. Though beta-glucuronidas e cleaved FG, the PG-iso compounds were resistant to the enzyme. The h alf-life of FG in a buffer solution at pH 7.4 and 37 degrees C was 4.4 h. The maximum stability of FG (half-life about 62 d) occurred at app roximately pH 3.2. Below pH 3.7, acyl migration products of FG were no t detected. Instead, the hydrolysis of FG to F and glucuronic acid was followed by the formation of 4-chloro-5-sulfamoylanthranilic acid (CS A), a secondary product in acidic media.