Linalool oxide pyranoid

The biotransformation of (/f,5)-Iinalool by fungi is a useful method for the preparation of natural linalool oxides. The stereospecific conversion of (J ,5)-linalool by Corynespora cassiicola DSM 62475 led to 5/f-configured furanoid linalool oxides and 55-configured pyranoid linalool oxides, both via bS -configured epoxylinalool as postulated intermediate (Figure 12.6). The biotransformation protocol affords an almost total conversion of the substrate with high enantioselectivities and a molar conversion yield close to 100% (Table 12.4). Pure linalool oxides are of interest for lavender notes in perfumery. ... 

Using a chiral column, coated with a definite modified cyclodextrin as the chiral stationary phase, the elution orders of furanoid and pyranoid linalool oxides are not comparable [11, 12]. Consistently, the chromatographic behaviour of diastereomers and/or enantiomers on modified cyclodextrins is not predictable (Fig. 17.1, Table 17.1). Even by changing the non-chiral polysiloxane part of the chiral stationary phase used, the order of elution may significantly be changed [13]. The reliable assignment of the elution order in enantio-cGC implies the coinjection of structurally well defined references [11-13]. 

Kreis P, Dietrich A, Mosandl A (1996) Elution order of the furanoid linalool oxides on common gas chromatographic phases and modified cyclodextrin phases. J Essent Oil Res 8 339 Weinert B, Wiist M, Mosandl A Hanssum H (1998) Stereoisomeric flavour compounds LXX-Vlff. Separation and structure elucidation of the pyranoid linalool oxide stereoisomers using common gas chromatographic phases, modified cyclodextrin phases and nuclear magnetic resonance spectroscopy. Phytochem Anal 9.T0... 

The biotransformation of linalool by Botrytis cinerea has also been described [60]. After addition of linalool to botrytised must, a series of transformation products was identified (E)- (49) and (Z)-2,6-dimethyl-2,7-octadiene-l,6-diol (48), trans- (76) and cw-furanoid linalool oxide (77), trans- (78) and c/s-pyranoid linalool oxide (79) and their acetates (80, 81), 3,9-epoxy-p-menth-1 -ene (75) and 2-methyl-2-vinyltetrahydrofuran-5-one (66) (unsaturated lactone), Fig. (11). Quantitative analysis however, showed that linalool was predominantly (> 90%) metabolised to ( )-2,6-dimethyl-2,7-octadiene-l,6-diol (49) by B. cinerea. The other compounds were only found as by-products in minor concentrations. 

Figure 9. Structures of additional glycoconjugates isolated from Riesling wine during this study B-D-glucopyranosides of 3-methylbutanol 21, 2-methyl-butanol 22, benzyl alcohol 23, 2-phenylethanol 24, furanoid linalool oxides (two diastereoisomers) 25, pyranoid linalool oxides (two diastereoisomers) 27, 3-oxo-7,8-dihydrc>-a-ionol 28, 3-oxo-a-ionol 29, 4,5-dihydro-vomifoliol 30, vomifoliol 31, and 7,8-dihydro-vomifoliol as well as the 6-O-B-D-apiofurano-syl-fi-D-glucopyranosides of furanoid linalool oxides (two diastereoisomers).

Isomers of 6,7-Epoxy-linalool as Precursors of Linalool Oxides. Previously, the triol (21) had been proposed as a possible precursor of the hydroxy ethers (14) and (15), the so-called linalool oxides(Fig-ure 8). At an acidic pH (<3.5) and/or during heat treatment (e.g., steam distillation/extraction), the triol (21) had been found to be decomposed to (14) and (15) (23,24). In these previous experiments no formation of the corresponding pyranoid linalool oxides (22) and (23) was observed. We evaluated the hypothesis that linalool oxides are formed from triol (21) under natural conditions of papaya pulp (i.e. pH 5.6) and could find no formation of linalool oxides. Even in model experiments carried out at pH 3.5, only traces of linalool oxides were detected after incubation of (21) for three days. As a result of these experiments the isomers of 6,7-epoxy-linalool have to be considered as the natural precursors of linalool oxides (14, 15) as recently suggested by Ohloff et al. (25). The latter s proposal was based on earlier findings obtained in a series of chemical reactions (9). 

In minor amounts ( <10 %) the corresponding (Z)-iso-mer, 2-vinyl-2-methyl-tetrahydrofuran-5-one, the four isomeric linalool oxides in their furanoid and pyrano-id forms, the isomeric acetates of pyranoid linalool oxides as well as 3,9-epoxy-p-menth-l-ene were identified as linalool metabolization products. Quantitative variations depending on the B cinerea strain used were observed. 

Conceptually, it is interesting to speculate on the bioconversion of inexpensive secondary metabolites to others of greater value. Along these lines, Schreier and co-workers use Botrytis cinera to convert linalool to a series of other terpenoids as well as to the furanoid and pyranoid linalool oxides. Reactions of this type are good examples of converting inexpensive, available aroma chemicals to higher valued products. 

FIGURE 19.18 Four stereoisomers of pyranoid linalool oxides. 

SSjOil-cA-pyranoid linalool oxide (3/J,6/f)-cw-pyranoid linalool oxide (-)-nerol oxide... 

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