Chirality in Biology
597
COOCH
3
O
7
3
O
O
O
R
O
O
S
O
R
O
O
7
4
(a)
(b)
(c)
(d)
(e)
(f)
R
Fig. 11
Enantiomeric fragrances.
(
a
)
=
(
3
R
,7
S
)methy
l
jasmonate;
(
b
)
=
(
3
R
)-muscone;
(
c
)
=
(
12
R
)
-Nirvanolide; (d),
(
e
)
=
Angelica
root oil compounds;
(
f
)
=
Galaxolide.
musk odorant with the trade name Galax-
olide (Fig. 11f) has four diastereoisomers
rated as follows: (4
S
,7
R
)-(
)–verypleas-
ant musk character; (4
R
,7
S
)-(
+
)–weak
,
uncharacteristic; (4
S
,7
S
)-(
)–musky,but
dry aspects; and (4
R
,7
R
)-(
+
)–very weak,
mainly fruity.
A new flavor material, 3-mercapto-2-
methylpentanol, has an odor described
as brothlike, leeklike, and sweaty – quite
a combination! It has been isolated from
volatiles of raw onions and in some
processed foods. With two chiral centers,
there are four stereoisomers; while all
apparently have the same general odor,
there are remarkable differences in their
odor thresholds in water and air. The
two
anti
enantiomers (2
R
,3
S
)and(2
S
,3
R
)
(Fig. 12a) had thresholds in water of 0.03
to 0.04
µ
gL
1
.Inair
,the(2
R
,3
S
)material
has an extremely low threshold, 0.00007
to 0.0002 ng L
1
and is ‘‘among the most
potent flavor compounds.’’ Its less-potent
enantiomer has air threshold of 0.003 to
0.007 ng L
1
. The air threshold values for
the
syn
enantiomers (2
R
,3
R
)and(2
S
,3
S
)
(Fig. 12b) could not be determined since
they were contaminated with 0.1 to 0.3%
of the very potent
anti
compounds.
Another odorant with two chiral centers
is ‘‘whiskey lactone,’’ 2-methyl-4-octalone,
extracted from oak woods during the
Fig. 12
Enantiomers of
3-mercapto-2-methylpentanol and
‘‘whiskey lactone.’’
(
a
)
=
anti
(2
R
,3
S
)-3-mercapto-2-methylpentanol;
(
b
)
=
syn
(2
R
,3
R
) diastereoisomer;
(
c
)
=
(
3
S
,4
S
)-2-methyl-4-octalone;
(
d
)
=
(
3
S
,4
R
) diastereoisomer.
OH
SH
3
2
1
(a)
OH
SH
(b)
(c)
O
O
3
4
(d)
O
O
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