Linalool enantiomers

Linalool is a major component in essential oils such as those of coriander, palmarosa, mace, petitigrain, Lippia alba and sweet orange flowers. (3i )(—)-Linalool is a main component in the oils of Ocimum species, including sweet basil, and in the oils of neroli, linaloe, bergamot, lavender and others. Linalool enantiomers in... 

Experimental investigations concerning the differences between sensory properties of linalool enantiomers were performed [61]. Its enantiomers display different spectra of sensory properties. The same authors [61] carried out estimations of the above-mentioned compoimds on human beings. The therapeutical effects of aroma of each optically active linalool were investigated before and after hearing environmental... 

This experiment was performed with a view to proving the effect of linalool enantiomers on the level of beta wave. The authors arrived at a conclusion that (-)-linalool influences the decrease of beta wave in contrast with (+)-linalool. 

The attained results may generally be well correlated with detection frequency method results and, to a lesser extent, with dilution methods. In the aforementioned research performed on the essential oils of Brazilian rosewood, this method was also used to give complementary information on the intensity of the linalool enantiomers [76]. 

Enantiomerically pure (5)-(+)-linalool was the main constituent in the extracts of the solitary bee Colletes cunicularius L. (Hymenoptera Col-letidae). Field tests using pure enantiomers and the racemate of linalool showed that the highest activity for male bees was for (5)-(+)-linalool. ... 

Properties. (zb)-Linalool [22564-99-4] is, like the individual enantiomers, a colorless liquid with a flowery-fresh odor, reminiscent of lily of the valley. However, the enantiomers dilfer slightly in odor [33]. Together with its esters, linalool is one of the most frequently used fragrance substances and is produced in large quantities. 

Single receptor neurons were tuned to a few structurally related components [383-384], while neurons in the antennae of individual insects were more responsive to speciflc enantiomers, e.g. (-i-)-linalool [377, 386]. 

Hotrienol was found for the first time in Ho leaf oil as the S enantiomer [7], but has been found since then in many natural sources for instance, the R enantiomer was found in black tea and in green tea. The product can be used in many flavours, such as eldertlower, grape, berry and honey flavours. It can be prepared from linalool obtained from citrus oils or Chinese Ho oils, but most linalool is obtained by synthesis from isoprene from petrochemical sources. 

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]. 

Linalool (3,7-dimethyl-l,6-octadien-3-ol) (62) occurs as one of its enantiomers in many essential oils, where it is often the main component. (/ )-(-)-Linalool for example occurs at a concentration of 80-85% in Ho oils from Cinnamomum camphora rosewood oil contains ca 80%. (S)-(+)-Linalool makes up 60-70% of coriander oil [26]. 

In the case of linalool the enantiomeric ratio was more variable between plants. In majority of investigated plants (R)-(-)-linalool dominates. The plants of the highest optical purity of (-)-Iinalool have been fovmd lavender Lavandula angustifolia), bergamot Citrus auranthium Bergamia), thyme Thymus vulgaris) and basil Ocimum basilicum). In a group of plants in which (S)-(+)-linalool dominates a practically pure enantiomer has been revealed in Robinia flowers Robinia pseudoacacia). 

An interesting variability is observed in plants from Rutaceae family. In bergamot (Citrus auranthium Bergamia), neroli and petitgrain (Citrus auranhtium ssp. amara), and lime oils (Citrus aurantifolia) the prevalence of (-)-linalool has been found. In orange (Citrus sinensis) and tangerine (Citrus reticulata) (+)-linalool is the dominant enantiomer, while in lemon (Citrus limon) and grapefruit (Citrus paradisi) the enantiomeric ratio of linalool is close to racemate [31,40]. 

Enantiodifferentiation Limonene is present in a purity exceeding 99% as the R(-i-)-enantiomer [45, 58]. Linalool is present in an enantiomeric excess of over 93% S(-H)-lina-lool. 

While limonene, analogous to Citrus sinensis oils, is present in an enantiomeric purity exceeding 99%, the ratio of the linalool antipodes is inverted. Of its enantiomers, R(-)-linalool is present in values exceeding 70% [48, 80, 90]. 

On-line coupling of enantio cGC with IRMS (enantio cGC-IRMS) is one of the latest developments in originspecific analysis of flavouring and fragrance compounds. Enantio-IRMS detects enantiomers of the same source with identical 5 C levels. As outlined in Fig. 6.45, linalool from Coriander oil is detected as an R(20%) S(80%) enantiomeric ratio with identical isotope levels of the enantiomers. 

Tacke et al45 synthesized the enantiomers of sila-linalool (61) as shown in Figure 11. The starting material 60 was converted into ( )-61, which was resolved by GC to give both (+)-61 and (—)-61. Both enantiomers were bioactive as tested by electroantennographic detection (EAD) on the males of the vernal solitary bee Colletes cunicularius. There was no major difference between the bioactivity of the sila-pheromone 61 and the natural linalool. The substitution of a carbon atom by silicon provides a good example of bioisosterism. 

Similarly, the synthesis of both enantiomers of linalool oxide was achieved... 

What really makes this synthesis useless is that it would give the wrong enantiomer of grand-isol (see the ring junction stereochemistry). While (/ )-( )-linalool is available in 100% ee, the (S) -(+)-enantiomer is both more expensive and available in only 64% ee. 

Although the structure and relative stereochemistry were easily determined by classical degradative and, later, synthetic studies, the absolute stereochemistry of the two enantiomers proved more challenging. Oxidative ozonolysis of (-i-)-ipomeamarone afforded a lactone, [a]o +7.4° (39), which had similar rotation to the same lactone (42) ([a]o +6.3°) prepared from / -linalool (43) (In this work (39) the sign of the optical rotation quoted was wrong, because, as determined later, the lactone prepared in this way has a negative rotation). On this basis, C-4 of (+)-ipomeamarone was... 

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