Odor Detection Thresholds and Enantiomeric Distributions of Several 4-Alkyl Substituted γ-Lactones in Australian Red Wine

Abstract

The individual enantiomers of gamma-octalactone (1), gamma-nonalactone (2), gamma-decalactone (3) and gamma-dodecalactone (4) have been synthesized. The (R) series of enantiomers was prepared from L-glutamic acid by a strategy involving deamination and reduction to (S)-5-oxo-2-tetrahydrofurancarboxaldehyde (S)-7. The different length side chains were introduced by a series of Wittig reactions, varying in the choice of phosphorane used. Hydrogenation then gave the final gamma-lactones 1-4. The (S) series of enantiomers was prepared in an analogous fashion beginning with d-glutamic acid. Aroma detection thresholds for all eight enantiomers were determined in a "bag in a box" dry red wine by the application of ASTM method E 679, employing a panel of 25 members. The lowest threshold determined was 8 microg/L for (R)-dodecalactone (4) while the highest threshold was 285 microg/L for (R)-nonalactone (2). With the exception of gamma-decalactone (3) there were statistically significant differences (at the 5% level) in aroma detection thresholds between the two enantiomers of the same lactone. A stable isotope method developed for quantification of the lactones 1-4 has been extended for use with chiral phase GC (Rt-betaDEXcst capillary column) allowing quantification of the individual enantiomers. The enantiomeric distribution of gamma-octalactone (1) and gamma-nonalactone (2) in seven botrytized wines and of 2 in a total of 34 red wines were thus determined; with few exceptions, the (R) enantiomer of gamma-nonalactone (2) was found to be more prevalent than its (S) counterpart in the dry red and botrytized white wines analyzed. The same was true for gamma-octalactone (1) in the botrytized white wines.

Gold-catalyzed stereoselective cycloisomerization of allenoic acids for two types of common natural γ-butyrolactones

“…It has been established that the two enantiomers of γ-alkylic γ-butyrolactones made some differences in odor quality and odor intensity 11 , 52 , 53 . Thus, we tried to synthesize both ( R ) and ( S )-γ-lactones by utilizing the current strategy.…”

“…7c ) 56 . ( R )-4-Decalactone is a sex pheromone of Osmoderma eremite released mainly or exclusively by male beetles 57 , which has also proven to be cytotoxic 58 , 59 , and synthesized with biocatalysts 26 , 58 , 59 or by other strategies 29 , 53 , 60 . Gram scale synthesis of ( R )-4-decalactone was also realized easily in 43% total yield for 4 steps with 94% ee (Fig.…”

Aromatic Potential of Bordeaux Grape Cultivars: Identification and Assays on 4-Oxononanoic Acid, a γ-Nonalactone Precursor

“…In fact, the intermediate 2 was found to be unstable and rapidly converted to compound 1 during the storage for a few days. In this step, Dess–Martin oxidation was preferred to Swern oxidation initially proposed by Cook et al Indeed, Dess–Martin periodinane use offers the safety and facilities of reaction and workup procedures. For the deuterium introduction in step c, isopropyl 4-oxononanoate ( 3 ) was carefully purified by column chromatography and treated under acidic conditions.…”

“…Racemic γ-nonalactone, reminiscent of a complex mixture of “coconut”, “peach”, and “cooked fruit”, has an aroma detection and recognition threshold of 9.7 and 27 μg/L, respectively, in model solution . Although both enantiomers have the similar cooked peach aroma descriptor in wine, the S enantiomer aroma detection threshold determined in red wine ( D th of 91 μg/L) was 3 times lower than for its R counterpart (284 μg/L) . Despite this compound being present at a low concentration, below its individual aroma detection threshold, this lactone together with the other lactones (with similar aroma properties) can contribute to the wine aroma as a result of additive effects .…”

“…n -Alkyl-substituted lactones are natural aroma compounds reminiscent of pleasant “coconut”, “fruity”, and “sweet” aromas. The absolute and relative configurations of lactones are used to influence their descriptors and detection thresholds. − In general, the R enantiomer exhibits a more intense aroma than S , antipode . Lactones have been detected in a wide variety of foods and beverages, such as vegetables, fruits, bread, butter, milk, coffee, and beer. ,, With their pleasant descriptors, they also play a key role in the flavor and fragrance industry …”