Yoshihiro Yaguchi

A Vibrational Circular Dichroism Approach to the Determination of the Absolute Configurations of Flavorous 5-Substituted-2(5H)-furanones

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.

Characterisation of odorant compounds and their biochemical formation in green tea with a low temperature storage process

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 LTPGTs 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.

Stereochemical studies of odorous 2-substituted-3(2H)-furanones by vibrational circular dichroism.

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.

Stereochemical study of a novel tautomeric furanone, homofuraneol

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.

Stereochemical Study of Chiral Tautomeric Flavorous Furanones by Vibrational Circular Dichroism

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.

Volatile Compounds from the Different Organs of Houttuynia cordata and Litsea cubeba (L. citriodora)

The volatile compounds obtained from the different organs of Houttuynia cordata (Saururaceae) and Litsea cubeba (Lauraceae) were analyzed by Gas Chromatography/Mass Spectrometry (GC/MS), Headspace Solid Phase Micro Extraction-Gas Chromatography/Mass Spectrometry (HS-SPME-GC/MS), and GC/olfactometry (GC/O). The major component of all parts of H. cordata is assigned as 4-tridecanone. Each organ produces myrcene as the major monoterpenoid. The major monoterpene in the rhizomes and roots was β-pinene instead of myrcene. 1-Decanal which was responsible for the unpleasant odor of this plant, was the predominant polyketide in both leaves and stems. The presence of 1-decanal was very poor in flowers, stem collected in summer, rhizomes, and roots. GC/MS analyses were very simple in case of the crude extracts of flowers. The content of sesquiterpenoids was extremely poor. (8Z)-Heptadecene, geranial, and neral were detected as the major components in Litsea cubeba. Odor-contributing components by GC/O analysis of the ether extract of the fresh flowers of L. cubeba were neral and geranial which played an important role in sweet-lemon fragrance of the flowers. The role of a high content of (8Z)-heptadecene was still unknown but it might play a significant role in the dispersion of the volatile monoterpene hydrocarbons and aldehydes. The flower volatiles of the Japanese L. cubeba were chemically quite different from those of the Chinese same species.

Characteristic Scent from the Tahitian Liverwort, Cyathodium foetidissim um

The volatile components of the Tahitian liverwort Cyathodium foetidissimum was analyzed using headspace solid phase micro-extraction (SPME) and GC-MS. Three volatile components, 4-methoxystyrene (24.4%), 3,4-dimethoxystyrene (28.7%), and skatole (15.9%) were identified as the major components from the fresh C. foetidissimum, along with several aliphatic aldehydes, n-octanal, n-nonanal, and n-decanal. However, (E)-2-nonenal recognized as aged malodor was not identified. In GC-O analysis, 2-aminoacetophenone was detected as one of the minor components with a strong aging note. In fact, C. foetidissimum showed the characteristic aging odor reminiscent the damp smell from old chest of drawers, or the civet like note with very strong feces and urine odor. The mixture consisted of 4-methoxystyrene, 3,4-dimethoxystyrene, and skatole in the detected ratio showed the sedative effect on CNV (contingent negative variation) measurement.

Comparative Study on Volatile Compounds of Alpinia japonica and Elettaria cardamomum

The volatile compounds obtained from the ether extracts, headspace gases and steam distillates of Alpinia japonica and Elettaria cardamomum were analyzed by GC/MS. Both species were rich sources of naturally rare fenchane-type monoterpenoids, fenchene, fenchone, fenchyl alcohol and its acetate, together with 1,8-cineole. The distributions of volatile sesquiterpenoids were very poor in both species. Chiralities of fenchone in A. japonica and E. cardamomum were 99% of (1S,4R)-(+)-form. Camphor in A. japonica is composed of a mixture of (1R,4R)-(+)-form (94.3%) and (1S,4S)-(-)-form (5.7%). On the other hand, E. cardamomum produced only (1R,4R)-(+)-camphor (99%).