Carvone, chirality

The difference m odor between (R) and (S) carvone results from their different behavior toward receptor sites m the nose It is believed that volatile molecules occupy only those odor receptors that have the proper shape to accommodate them Because the receptor sites are themselves chiral one enantiomer may fit one kind of receptor while the other enantiomer fits a different kind An analogy that can be drawn is to hands and gloves Your left hand and your right hand are enantiomers You can place your left hand into a left glove but not into a right one The receptor (the glove) can accommodate one enantiomer of a chiral object (your hand) but not the other... 

The oil possesses moderate antibacterial and strong antifungal properties. Thus the appHcation of the oil to the cmst of cheese could serve to prevent the formation of mycotoxia ia the cheese. The optical purity of the carvone ia caraway has been determined usiag a chiral gc column (72). It was found to be (i )(+) = 97.64% and (5 )(—) = 2.36%. 

The example given above of the selection of deoxycholic acid as a SM for the synthesis of cortisol also illustrates the use of a chiral natural substance as synthetic precursor of a chiral TGT. Here the matching process involves a mapping of individual stereocenters as well as rings, functional groups, etc. The synthesis of helminthosporal (105) from (-i-)-carvone (106)21 and the synthesis of picrotoxinin (107) from (-)-carvone (108)22 amply demonstrate this approach employing terpenes as chiral SM s. 

Each of the molecules below (carvone, ibuprofen anc limonene) incorporates a single chiral center. Identify ii and draw both R and S forms of each. 

Construction of the A ring fragment starts with epoxidation of chiral d-carvone (114) to afford epoxide 115. 

Figure 8. Equatorial el,e2, e3 and axial al,a2, a3 conformations of the carvone molecule. The asymmetric (chiral) carbon is shaded light gray, the =CH2 carbon in the isopropenyl tail is shaded mid-gray and the carbonyl oxygen atom is shaded dark gray. Taken from Ref. [38].

Figure 10. The CMS-Xa predictions for cross-section, the anisotropy parameter —P/2), and the chiral parameter in the carbonyl C li photoionization of (R)-carvone (I) and its indicated derivatives.

Results for these CEBEs are presented in Table 1. As can be seen, for the carvone variants I-V the various substitutions have absolutely no effect at the carbonyl C=0 core, and are barely significant at the chiral center that lies between the carbonyl and substituent groups in these molecules. Only upon fluorine substitution at the tail (molecule VI) does the C=0 CEBE shift by one-half of an electronvolt the second F atom substitution adjacent to the C=0 in the difluoro derivative, VII contributes a further 0.6-eV shift. This effect can be rationalized due to the electron-withdrawing power of an F atom. Paradoxically, it is these fluorine-substituted derivatives, VI, VII, that arguably produce b curves most similar to the original carvone conformer, I, yet they are the only ones to produce a perturbation of the ground-state electron density at the C li core. This contributes further evidence to suggest that, at least for the C li... 

The list of molecules whose PECD has been experimentally studied is quickly expanding, and in the VUV valence shell region now includes the prototypical chiral species camphor [36, 64, 65], bromocamphor [65, 80], fenchone and carvone [38], methyl oxirane [62, 63], glycidol [37, 38], and 3-hydroxytetrahy-drofuran [61]. Studies of camphor [56], fenchone [38], and carvone [55] have all been extended to cover the SXR C li core region. 

Equation (81)), while the other two C=C double bonds in the structure are intact. Under the same reaction conditions, the racemic carvone is also resolved kinetically with a KR/KS ratio of 33 1. Asymmetric hydrogenation of a,/Tacetylenic ketones to chiral propargylic alcohols is still unavailable. 

At the cellular level, the various types of receptor, transporter, enzyme and ion charmel are all chiral in form. Thus although the enantiomers of a drug may have identical physicochemical properties, the way in which they may interact with chiral targets at the level of the cell will give rise to different pharmacod)mamic and pharmacokinetic properties. A few simple examples will illustrate how taste and olfactory receptors can differentiate between enantiomers. Thus R-carvone tastes like spearmint whereas the S-isomer tastes like caraway. Similarly, R-limolene smells like lemon whereas the S-enantiomer tastes of orange. 

Ravid U, Putievsky E, Katzir I, Weinstein V, Ikan R, Chiral GC analysis of (5)(- -)- and (i )(—)-carvone with high enantiomeric purity in caraway, dill and spearmint oils. Flavour Fragr/7 289—292, 1992. 

Figure 2.1 Examples of chiral molecules where the enantiomers have different biological activity. ( -Carvone tastes of caraway while the (R)-enantiomer tastes of spearmint. The (S)-form of asparagine tastes...

FIGURE 1-23 Stereoisomers distinguishable by smell and taste in humans, (a) Two stereoisomers of carvone R) carvone (isolated from spearmint oil) has the characteristic fragrance of spearmint (S)-carvone (from caraway seed oil) smells like caraway, (b) Aspartame, the artificial sweetener sold under the trade name NutraSweet, is easily distinguishable by taste receptors from its bitter-tasting stereoisomer, although the two differ only in the configuration at one of the two chiral carbon atoms. 

For example, our ability to taste and smell is regulated by chiral molecules in our mouths and noses that act as receptors to sense foreign substances. We can anticipate, then, that enantiomers may interact differently with the receptor molecules and induce different sensations. This appears to be the case. The two enantiomers of the amino acid, leucine, for example, have different tastes—one is bitter, whereas the other is sweet. Enantiomers also can smell different, as is known from the odors of the two carvones. One has the odor of caraway and the other of spearmint. 

Epoxide is an important intermediate for various bioactive compounds, so the demand for the chiral epoxide is increasing. Epoxide hydrolase can hydrolyze epoxide enantioselectively (Figure 20).21 For example, Aspergillus niger was used for the hydrolysis of carvone epoxide (Figure 20(a)).2 11 In the reaction of styrene oxide, the... 

In semipreparative chromatography, the second eluted enantiomer is prone to contamination by the first eluted enantiomer. The second eluted enantiomer can be reverted to the first eluted enantiomer when a CSP of opposite chirality is used. Since both enantiomers of carvone are readily available as starting material for the preparation of the CSP Ni-(CAR)2 one of the two enantiomeric columns can be selected in an effort to elute the enantiomer of interest as a first fraction. 

The receptor site for (+)-carvone and (-)-carvone must be chiral such that the... 

Both a- and P-pinenes are popular starting materials for the synthesis of other monoterpene chiral synthons such as carvone, terpineol, and camphor (vide infra). Reactions leading to other monoterpenes are briefly summarized in Figure 5.1. Treatment of a-pinene with lead tetraacetate followed by rearrangement gives trans-verbenyl acetate (7), which is hydrolyzed to yield trans-verbenol (8) 8 Subsequent oxidation of 8 gives verbenone (9), which can be reduced to give cw-verbenol... 

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