598
Chirality in Biology
aging process for wines and spirits. The
major natural odor material is the (3
S
,4
S
)-
cis
-compound (Fig. 12c) with a coconut,
lactonelike odor. Some flowery, lactonelike
(3
S
,4
R
)-
trans
-component is also present
(Fig. 12d). Substitution of one or both
oxygen atoms with sulfur gave signi±cant
odor changes.
While many enantiomeric odor discrim-
inations involve pleasant, floral, or fruity
odors, nature also produces many foul
odors. For instance the microbial prod-
uct,
geosmin,
trans
-1,10-dimethyl-
trans
-
decalol, is known for its unpleasant moldy,
earthy odor, with the (
) enantiomer be-
ing more odoriferous than the (
+
)form
.
The odor thresholds in water are also very
different: (
), 9
.
5
±
1
.
3ngL
1
,and(
+
),
78
±
12 ng L
1
. Enantio-MGDC analysis
(see later) of wines with an earthy odor
revealed signi±cant levels of (
)-geosmin.
This enantiomer was also found in some
grape juices, probably from the growth of
microorganisms.
Gas chromatography has been a valu-
able tool in studying the volatile compo-
nents of the widely used essential oils.
Column packings able to separate enan-
tiomers (‘‘chiral chromatography’’) have
greatly expanded the scope and value
of this technique, as have ‘‘hyphenated’’
techniques,
using
mass
spectrometry;
for example, enantioselective multidimen-
sional
gas-chromatography
mass
spec-
trometry (enantio-MDGC-MS), and gas-
chromatography
pyrolysis-isotope
mass
spectrometry. One group, using various
gas chromatographic techniques, has pub-
lished a series of papers titled ‘‘Stereoiso-
meric Flavor Components’’ that reached
number LXXXII in 1999.
These techniques yield important basic
scienti±c information and have practical
applications. By comparing an authentic
natural oil sample with other samples, the
presence of unnatural, often chemically
synthetic, components can be detected.
The important lavender oil has several
odorants, including linalool and linalyl
acetate; (
R
)-(
)-linalool has the character-
istic lavender odor, (
S
)-(
+
)-linalool, has a
petitgrain-like odor (i.e. an odor of bitter
or sour orange). For these materials, gen-
uine lavender oil must contain at least 85%
enantiomeric excess of (
R
)-(
)-linalool and
at least 95% enantiomeric excess of (
R
)-
(
)-linalyl acetate. In a recent study, ±ve
samples of ‘‘lavender oil’’ were found to be
adulterated with racemic, synthetic mate-
rials (see Table 1).
Tab. 1
Enantiospecifc analysis oF samples oF oil oF
lavender.
Sample
Linalyl acetate
Linalool
(R)
(S)
(R)
(S)
15
2
.
9
a
47.1
70.7
29.3
2
55.7
44.3
55.5
44.6
3
51.8
48.2
62.0
38.0
4
52.0
48.0
69.7
30.3
5
53.3
46.7
60.8
39.2
Authentic
95.0 (minimum)
85.0 (minimum)
a
The values given are percentage compositions.
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