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leads to the rose-like phenyl ethyl alcohol [10.35] and phenylacetaldehyde
[10.26], which are in turn precursors to the cheesy phenylacetic acid
[10.36].
[10.34] [10.26] [10.35] [10.36]
The 'C6 wound gases', i.e.
cis
-3-hexenol [10.13],
trans
-2-hexenal [10.37] and
trans
-2-hexenol [10.38], are produced by plants as a by-product of cellular
damage, as molecular oxygen, a deadly cytotoxin, is 'trapped' by reaction with the
highly unsaturated carboxylic linolenic acid. We can use the same chemistry in
the manufacture of these aroma chemicals. Linoleic acid [10.39], readily available
from vegetable oils, is treated with lipoxygenase and the resulting hydroperoxide
[10.40] cleaved with (unsurprisingly) hydroperoxide lyase to give
cis
-3-hexenal
[10.41], which rearranges to
trans
-2-hexenal [10.37]. This can then be reduced by
bakers' yeast (Seebach
et al.
1985) to the alcohol [10.38], which in turn can be
converted to esters such as the acetate [10.42].
Cis
-3-hexenal can also be reduced
to give
cis
-3-hexenol [10.13], but at the moment this is not economic compared
with its isolation from mint oil - though, of course, the production of this by the
mint plant utilises exactly the same chemistry!
[10.39]
[10.40]
[10.13] [10.41] [10.37]
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