596
Chirality in Biology
levels of impurities in materials under in-
vestigation. Testing differences also arise
from variations in individual physiology,
past experience with a given odor, and
fatigue
among
members
of
a
testing
panel. Nevertheless, careful experiments
have established a spearmint odor for
(
R
)-carvone and a caraway odor for (
S
)-
carvone. These materials are the major
components of respectively oil of pep-
permint and oil of caraway. Important
evidence was obtained by ingenious chem-
ical inversions of one enantiomer into
the other, the inversions resulting in very
speciFc changes of odor; one sequence
was (
R
)-(
)-carvone
(
spearmint
)
(
S
)
-
(
+
)-carvone
(
caraway
)
(
R
)
-(
)-carvone
(spearmint). The inversion was repeated
similarly, starting with (
S
)-(
+
)-carvone.
Recent, careful testing has conFrmed
that the carvone enantiomers are dis-
tinguishable by odor, and this was also
true for enantiomers of
α
-pinene and
limonene. Most members of this panel
(20 subjects), however, could not distin-
guish enantiomers of 2-butanol, camphor,
β
-citronellol, fenchone, menthol, rose ox-
ide, and
α
-terpineol. The discriminatory
ability between enantiomers is apparently
substance-speciFc and is not a general
phenomenon. There are probably speciFc
enantioselective odor receptors for some
but not all volatile enantiomers. Squirrel
monkeys showed discriminatory abilities
similar to those of humans; unlike hu-
mans, they could distinguish the fenchone
enantiomers.
Rats readily discriminated the carvone
enantiomers and, unlike humans, also
distinguished enantiomers of fenchone,
2-butanol, and 2-octanol. In a study of the
rat olfactory bulb, each enantiomer pro-
duced a widespread and distinct pattern
of active glomeruli. Each member of an
enantiomeric pair preferentially activated
one or more glomeruli. In mole rats
(
Spalax ehrenbergi
), some differential re-
sponses were observed to enantiomers
of
carvone,
citronellol,
and
fenchone.
The animals responded to one enan-
tiomer but were indifferent to or did
not smell the other [(
S
)-(
+
)-carvone, (
)-
citronellol, (
+
)-fenchone]. (
R
)-(
)-Carvone
was attractive to both sexes and females
were attracted to (
)-fenchone. Both sexes
were
repelled
by
(
+
)-citronellol.
±ree-
flying honeybees discriminated carvone,
β
-citronellol, limonene, menthol, and
α
-
pinene enantiomers but not those of
2-butanol, camphor, fenchone, rose oxide,
and
α
-terpineol.
±or the
cis
-methyl jasmonates, two di-
astereoisomeric pairs have been tested
(±ig. 11). Only the (3
R
,7
S
)and(3
R
,7
R
)di
-
astereoisomers have an odor described as
‘‘typically floral, jasminic, slightly fruity,’’
and the odor of natural ‘‘methyl jas-
monate’’ is due largely to the (3
R
,7
S
)-
(
+
) material (±ig. 11a). The (3
S
,7
R
)and
(3
S
,7
S
) materials were odorless.
The ‘‘musk’’ odor is important in per-
fumery, and several synthetic odorants
are used commercially. ±or the naturally
occurring
(3
R
)-(
)-muscone
(±ig. 11b),
t
h
em
u
s
kn
o
t
ew
a
s‘
v
e
r
yn
i
c
e
,r
i
c
h
,
and powerful’’ but for the enantiomer,
(3
S
)-(
+
)-muscone, the note was ‘‘poor
and less strong.’’ The compound shown
in ±ig. 11(d) ‘‘has an animalic tonality
with camphoraceous aspects,’’ while the
enantiomer (±ig. 11e) had a musk note
‘‘with a sandalwood tonality.’’ Both are
found in
Angelica
root oil in a ratio of
29 : 72 for structures (d) and (e) (±ig. 11).
In another case, (12
R
,9Z)-12-methyl-14-
tetradec-9-enolide (trade name, Nirvano-
lide,
±ig. 11c)
possessed
an
‘‘intense
musky, fruity, powdery odor with lactonic
nuances.’’ Its enantiomer was odorless.
The commercially important polycyclic
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