2,5-dimethyl-4-hydroxy-3 -furanone formation

Scheme 13.14 Formation of 4-hydroxy-2,5-dimethyl-(2H)-furanone from rhamnose...

Naim, M., S. Wainish, U. Zehavi, H. Peleg, R.L. Rouseff, S. Nagy, Inhibition by thiol compounds of off-flavor formation in stored orange juice. I. Effect of L-cysteine and N-acetyl-L-cysteine on 2,5-dimethyl-4-hydroxy-3(2H)-furanone formation, J. Agric. Food Chem., 41(9), p. 1355, 1993. 

The reaction of a-bromoacetals with trimethylsilylenolates catalyzed by titanium tetrachloride provides /3-alkoxy-y-bromoketones, which are useful furan precursors (Scheme 33) (75CL527). A new synthesis of acylfurans is exemplified by the formation of the 3-acetyl derivative (146) by heating the brdmoalkene (145) (78JOC4596). 2,2-Dimethyl-3(2//)-furanone (148) has been synthesized from 3-hydroxy-3-methylbutan-2-one treatment with sodium hydride and ethyl formate gave the hydroxymethylene derivative (147), which was cyclized and dehydrated to the furanone (148) with hydrochloric acid (Scheme 34) (71TL4891). O... 

Blank, I., Lin, J., Fumeaux, R., Welti, D.H., and Fay, L.B. 1996. Formation of 3-hydroxy-4,5-di-methyl-2(5H)-furanone (sotolone) from 4-hy-droxy-L-isoleucine and 3-amino-4,5-dimethyl-3,4-dihydro-2(5)-furanone. J. Agric. Food Chem. 44 1851-1856. 

FIGURE 7.11 Formation of Sotolon (3-hydroxy-4,5-dimethyl-2(5H)-furanone) in wines by aldol condensation of acetaldehyde and 2-oxobutanoic acid followed by lactoni-zation (Kobayashi, 1989). 

A maltol-ammonia browning reaction produced thirteen pyrazines, two pyrroles, two oxazoles, and one pyridine (12). The major products of this system were 2-ethyl-3-hydroxy-6-methylpyridine and 2-ethyl-3,6-dimethylpyrazine. It is difficult to construct possible formation mechanisms for these compounds from maltol and ammonia. All the carbon atoms must come from maltol. It is possible, then, that maltol degrades into smaller carbon units and that these fragments recombine to form larger carbon units, producing these compounds. Recently, the formation of thiophenones and thiophenes from the reaction of 2,5-dimethyl-4-hydroxy-3(2H)-furanone and cysteine or cystine was reported (13. 14). All these reaction mixtures were reported to possess a cooked meat-like flavor. 

Dimethoxy Phenol 3,4-Dimethyl 1,2-Cyclopen tandione 5-Ethyl 3-Hydroxy 4-Methyl 2(5H)-Furanone 3-Ethyl Pyridine Furfuryl Mercaptan Geranyl Isovalerate 2,3 -Heptandione (Z)-3-Hexenyl Butyrate (Z)-3-Hexenyl Formate Hexyl Butyrate Hexyl Hexanoate Isoamyl Isobutyrate Isobutyl Formate Isobutyl Hexanoate Linalool Oxide... 

Fig. 3.26 Formation of4-hydroxy-2,5-dimethyl-3(2H)-furanone from 1-deoxyhexosone 3.2.3.3.2 Lipid Oxidation...

Blank, I., Fay, L.B. Formation of 4-hydroxy-2,5-dimethyl-3(2//)-furanone and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2//)-furanone through MaiUard reaction based on pentose sugars. J. Agric. Food Chem. 1996, 44, 531-536. 

In addition, other work showed that 3-hydroxy-4,5-dimethyl-2(5H)-furanone can be formed thanks to a Maillard reaction of hexoses and pentoses in the presence of cysteine 20). Due to the non-linear structure of Sotolon, its formation cannot simply be explained directly from sugar cyclization during tire Maillard reaction, like other furanones such as Furaneol. Hence, it is likely tliat Sotolon results from rearrangement of Amadori products of low molecular weight like butan-2,3-dione (diacetyl) and hydroxyacetaldehyde, via an aldol condensation (Figure 6). 

In addition to terpenes, carbohydrates serve as a precursor of furanones in plants. The formation of 2,5-dimethyl-4-hydroxy-2H-furan-3-one (DMHF) is an example. This compound, and various forms thereof, are key to the aroma of strawberry. Several researchers have studied the biochemical pathways responsible for the formation of this compound [34,35]. The pathway presented in Figure 4.10 illustrates DMHF formation from its key precursor, 6-deoxy-D-fructose. 

Among other compounds, C-3 fragments are also precursors for the formation of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (II, furaneol), which can be formed, e. g., from 2-hydroxypropanal and its oxidation product, 2-oxopropanal (I in Formula 4.47). The substitution of 2-oxobutanal for 2-oxopropanal yields the homologous ethylfuraneol. In a similar way, 3-hydroxy-... 

In the course of the Maillard reaction, de-oxyosones and reductones, e. g., acetylformoin (cf. Ill, Formula 4.67), are formed. They cttn react to give enol and triketo compounds via an addition with disproportionation (Formula 4.86). Redox reactions of this type can explain the formation of products which are not possible according to the reactions described till now. In fact, it has recently been found that, for example, glucose 6-phosphate and fructose-1,6-diphosphate, which occur in baker s yeast and muscle, form 4-hydroxy-2,5-dimethyl-3(2H)-furanone to a large extent. Since the formation from hexoses (or hexose phosphates) is not explainable, reduction of the intermediate acetylformoin (Formula 4.87) must have occurred. As shown, this reduction can proceed through acetylformoin itself or other reductones, e. g., ascorbic acid. Such re-... 

I. Blank, J. Lin, L. B. Fay, and R. Fumeaux, Formation of 3-hydroxy-4,5-dimethyl-2(5fl)-furanone (sotolon) from 4-hydroxy-L-isoleucine, Bioflavour 95 (P. X. Etie-vant and P. Schreier, eds.), INRA Editions (Les Colloques, no. 75), Paris, 1995, p. 385. 

T. Koenig, B. Gutsche, M. Hartl, R. Huebscher, P. Schreier, and W. Schwab, 3-Hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon) causing an off-flavor elucidation of its formation pathways during storage of citrus soft drinks, J. Agric. Food Chem. 47 3288 (1999). 

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