Sotolon (1) and maple furanone (2) are naturally occurring chiral furanones. These 5-substituted-2(5H)-furanones are industrially significant aroma compounds due to their characteristic organoleptic properties and extraordinarily low odor thresholds. Each enantiomer of 1 and 2 was successfully obtained by preparative enantioselective supercritical fluid chromatography. The absolute configuration of 1 was confirmed as (R)-(-)-1 and (S)-(+)-1 by adopting the vibrational circular dichroism (VCD) approach. The absolute configuration of 2, which has remained ambiguous since its discovery in 1957, was determined as (R)-(+)-2 and (S)-(-)-2 for the first time by the VCD technique. Surprisingly, the signs of the optical rotation of 2 are opposite of those of 1 regardless of their identical absolute configurations. This observation emphasizes the risk in absolute configurational assignments based on comparison of optical rotation signs of similar structures. Odor evaluation of the enantiomers of 2 revealed different odor intensities.

We produced low temperature (15 °C) processed green tea (LTPGT) with higher aroma contents than normal green tea (Sencha). Normal temperature processed green tea (NTPGT), involved storing at 25 °C, and Sencha had no storing process. Sensory evaluation showed LTPGT had higher levels of floral and sweet odorants than NTPGT and Sencha. Aroma extract dilution analysis and gas chromatography-mass spectrometry-olfactometry indicated LTPGT had 12 aroma compounds with high factor dilution values (FD). Amongst LTPGT's 12 compounds, indole, jasmine lactone, cis-jasmone, coumarin, and methyl epijasmonate contributed to floral, fruity and sweet characters. In particular, indole increased initially, peaking at 16 h, then gradually decreased. Feeding experiments suggested [(15)N]indole and [(15)N]oxygenated indoles (OX-indoles) were produced from [(15)N]anthranilic acid. We proposed the increase in indole was due to transformation of anthranilic acid during the 16 h storage and the subsequent decline in indole level was due to its conversion to OX-indoles.

Chiral naturally occurring aroma compounds often exhibit enantiomeric excesses due to their stereoselective biogenesis. In general, significant organoleptic differences are perceived between these enantiomers. Chiral 2-substituted-3(2H)-furanones, featuring a unique keto-enol tautomer, the cause of their racemization, have been known to play an important role in flavor because of their extremely low threshold values and their burnt sugar odor characteristics. Since the discovery of these important aroma chemicals, they have been used in large quantities as raw materials in the flavor and fragrance industry. However, absolute configurations of these furanone derivatives have remained ambiguous for the past 40 years. Here optical resolutions of 2,5-dimethyl-4-hydroxy-3(2H)-furanone, 2,5-dimethyl-4-methoxy-3(2H)-furanone, and 4-acetoxy-2,5-dimethyl-3(2H)-furanone were accomplished using chiral CO(2) supercritical fluid chromatography (SFC). Their absolute configurations were unraveled for the first time using the vibrational circular dichroism (VCD) technique as well as by chemical relay reactions. Odor evaluation of each enantiomer revealed relationships between their configurations and odor activities.

A mixture of tautomers with unique keto-enol structures, 5-ethyl-4-hydroxy-2-methylfuran-3(2H)-one and 2-ethyl-4-hydroxy-5-methylfuran-3(2H)-one (EHMF, homofuraneol, 1a and 1b), comprises four structural isomers including their enantiomers. The four isomers were successfully separated by chromatographic optical resolution, and their odor evaluation was performed. Determination of the absolute chemistry of 1a and 1b were accomplished for the first time by direct measurement of the VCD spectra of their methyl ether derivatives 4a and 4b compared with the calculated ones as well as chemical relay reaction. The relationship between odor characteristics and stereochemistry was also examined.

2-Substituted-3(2H)-furanone derivatives are industrially significant aroma compounds possessing a unique keto-enol tautomeric feature causing their racemization. Absolute configurations of two flavorous furanones, which have remained unclear for the past 40 years since their discovery, were clarified by the vibrational circular dichroism technique as well as chemical relay reactions. Odor evaluation of each enantiomer revealed relationships between their configurations and their odor activities.The naturally occurring furanones represented by 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF, 1), 2,5-dimethyl-4-methoxy-3(2H)-furanone (DMMF, 2), and 2(or 5)-ethyl-4-hydroxy-5(or 2)-methyl-3(2H)-furanone (EMHF, 3a or 3b) are major flavor components in numerous fruits such as pineapples and strawberries. 1 (Compounds 1 and 2 have frequently been called "Furaneol" as a commodity name and "mesifuran", respectively. "Furaneol" is a registered trademark of Firmenich SA, Switzerland.) They have also been found in a range of highly cooked foodstuffs as pleasant odor components that are formed mainly via Maillard reactions between sugars and amino acids during heating. 1 These furanones are known to play an important role in flavor because of their extremely low threshold values and their burnt sugar odor characteristics. For instance, odor threshold values in water for 1, 2, and 3 are 60, 0.4, and 20 ppb, respectively. 2 Therefore, these compounds have been investigated extensively as significant flavor chemicals. Since the discovery of these important aroma chemicals, large quantities have been utilized as raw materials in the flavor and fragrance industry, with worldwide annual consumption of up to almost 100 t. 3 These flavor-related furanones are believed to be biosynthesized via a glycoside from 6-deoxy-L-mannose in plants. 1a,4 However, most of the naturally occurring ones were isolated as optically inactive compounds 1a,5 due to their unique keto-enol tautomeric structures causing racemization. † Takasago International Corporation.