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

Abstract

The proposed formation of 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolone) from 4-hydroxy-l-isoleucine (1) and the corresponding lactone 3-amino-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 compounds in a phosphate buffer at pH 5 at 100 °C for 1 h. The amount of sotolone was quantified by stable isotope dilution assays using 13C2-labeled sotolone as internal standard and GC-MS operating in the selected ion monitoring mode. In general, α-ketoaldehydes were found to be more reactive than α-diketones. Methylglyoxal gave rise to about 64 μg sotolone per mg 1 (7.4 mol %) compared to less than 1 μg (<0.1 mol %) when reacted with 2,3-pentanedione. Using 2 as the starting material, the yields were increased to 274 μg (35.9 mol %) and 5.4 μg (0.7 mol %), respectively. The optimum pH of the reaction with HIL was 5, representing the best compromise between the lactonization step and the amino−carbonyl reaction. Significant amounts of sotolone were generated only at temperatures higher than 70 °C. The yield increased over a period of 10 h to about 210 μg/mg 1 (23.8 mol %). The Strecker degradation of 1, resulting in 3-hydroxy-2-methylbutanal, was a competitive reaction to the formation of sotolone. Keywords: 3-Hydroxy-4,5-dimethyl-2(5H)-furanone (sotolone); 4-hydroxy-l-isoleucine; oxidative deamination; Strecker degradation; quantification by isotope dilution assay; model system studies; synthesis

Sotolone Production by Hairy Root Cultures of Trigonella foenum-graecum in Airlift with Mesh Bioreactors

“…On the other hand, Blank et al (27) found that sotolone was generated in model systems by thermally induced oxidative deamination of HIL through 3-amino-4,5-dimethyl-3,4-dihydro-2(5H)-furanone, using different carbonyl compounds as carbonyl reactant. In the present work we were unable to find the HIL oxidative deamination product (10). However, the compound 3-amino-4,5-dimethyl-2(5)-furanone, previously found in L. helvus (29), with a molecular weight and mass spectrum close to those of sotolone, was clearly present in the hairy root cultures ( Figure 5; Table 2).…”

“…From the synthetic pathways postulated for sotolone formation (12,26,(56)(57)(58), it has been suggested that this compound might originate from HIL. This hydroxylated amino acid is usually present in T. foenumgraecum (59,60) and L. helvus (29), a mushroom from Europe.…”

“…On the other hand, 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolone), a furanone component of the characteristic aroma of Trigonella foenum-graecum (fenugreek) seeds (10,11), is one of the most important highvalue natural flavoring substances (12,13). Because of its strong reminiscent odor, sotolone has been widely used as an aroma in the food (14) and tobacco industries (15).…”

Characterisation of volatile compounds in Tunisian fenugreek seeds

“…This molecule has great flavouring potential, with an estimated threshold value of 0.02 ng L À1 in air and of 0.3 lg kg À1 in water, which are quite low (Blank & Schieberle, 1993;Blank et al, 1997). Its precursors in the seeds are suspected to be 4-hydroxyisoleucine, which is the major amino acid present and whose content decreases during germination, and its lactone [3-amino-4,5-dimethyl-3,4-dihydro-2(5H)-furanone] (Blank, Lin, Fumeaux, Welti, & Fay, 1996;Blank et al, 1997;Girardon et al, 1986). However, other molecules are also involved in the strong odour characteristic of fenugreek, as other potent aroma compounds have been reported in fenugreek using different modes of 0308-8146/$ -see front matter Ó 2009 Elsevier Ltd. All rights reserved.…”

Volatiles responsible for the seasoning‐like flavour of cell cultures of Laetiporus sulphureus

“…L-Isoleucine, found in micromolar concentration (189 μM; Table 1) in the culture liquid, is an obvious precursor of L-hydroxyisoleucine, which was identified in the culture medium (Figure 2). This compound may, in turn, have served as a precursor of the corresponding oxoacid, which would then cyclize to sotolon (9) and the related furanone (10) (Figures 1, 3c). [15] The same oxoacid could explain the presence of 4,5-dimethyl-dihydrofuran-2-one (4).…”