FORMATION OF 3-HYDROXY-4,5-DIMETHYL-2(5H)-FURANONE (SOTOLONE) FROM 4-HYDROXY-L-ISOLEUCINE AND 3-AMINO-4,5-DIMETHYL-3,4-DIHYDRO-2(5H)-FURANONE

The proposed formation of 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotol one) from 4-hydroxy-L-isoleucine (1) and the corresponding lactone 3-a mino-4,5-dimethyl-3,4-dihydro-2(5H)-furanone (2) by thermally induced oxidative deamination was corroborated. The formation of sotolone was studied in model systems by reacting 1 or 2 with different carbonyl co mpounds in a phosphate buffer at pH 5 at 100 degrees C for 1 h. The am ount of sotolone was quantified by stable isotope dilution assays usin g C-13(2)-labeled sotolone as internal standard and GC-MS operating in the selected ion monitoring mode. In general, alpha-ketoaldehydes wer e found to be more reactive than alpha-diketones. Methylglyoxal gave r ise to about 64 mu g sotolone per mg 1 (7.4 mol %) compared to less th an 1 mu g (<0.1 mol %) when reacted with 2,3-pentanedione. Using 2 as the starting material, the yields were increased to 274 mu g (35.9 mol %) and 5.4 mu g (0.7 mol %), respectively. The optimum pH of the reac tion with HIL was 5, representing the best compromise between the lact onization step and the amino-carbonyl reaction. Significant amounts of sotolone were generated only at temperatures higher than 70 degrees C . The yield increased over a period of 10 h to about 210 mu g/mg 1 (23 .8 mol %). The Strecker degradation of 1, resulting in 3-hydroxy-2-met hylbutanal, was a competitive reaction to the formation of sotolone.