Biomedical Engineering Reference
In-Depth Information
OH
HO
H
EDDA, Et
3
N
Xylene, reflux, 48 h
65%
OHC
+
H
OH
O
O
O
220
221
(+)-Machaeriol B
222
SCHEME 9.37
Synthesis of machaeriol
222
by Lee and coworkers.
(
using a catalytic amount of EDDA in the presence of Et
3
Nin
refluxing xylene to afford
)-(3
S
)-citronellal
221
in 65% yield (Scheme 9.37).
Spinosyns such as spinosyn A (
222
), which are sold as a
3:1 mixture, are very powerful insecticides that are characterized by their very low
toxicity toward mammals, fish, and bees. They are produced by fermentation of the
microorganism
Saccharopolyspora spinosa
. In an effort to overcome developing
resistances, Tietze and coworkers are preparing analogues [83]. Since it has been
shown that sugar moieties are necessary for the bioactivity of these compounds, they
developed a three-component domino process for the synthesis of (
223
) and spinosyn D (
224
)-forosamine
(
230
). For the preparation, a mixture of nitroacetone
225
, formaldehyde
226
, and
ethyl vinyl ether
was treated with a catalytic amount of ethylenediammonium
diacetate. It can be assumed that first an 1,3-oxa butadiene
227
is formed by a
Knoevenagel condensation that then reacts with the enol ether to give dihydropyran
229
228
. It follows a hydrogenation of the double bond and a reduction of the nitro group
using NaBH
4
. The final step in the synthesis after resolution by chromatography on a
chiral support is the anomeric deprotection using acid (Scheme 9.38).
Recently, Tietze and coworkers developed inductor
for the asymmetric
allylation of methyl ketones. The latter can be obtained via an enantioselective
reduction followed a silylation of benzyl phenyl ketone [84]. Then they used
233
233
in the enantioselective total synthesis of the reported structure [85] of
OEt
O
OEt
O
227
O
O
OH
steps
80°C, 3 h
37%
+
O
O
2
N
O
2
N
O
2
N
Me
2
N
H
225
228
229
230
H
226
OMe
O
MeO
O
NMe
2
MeO
O
H
H
O
O
O
Spinosyn A (R = H;
223
)
Spinosyn D (R = Me;
224
)
O
H
H
R
SCHEME 9.38
Synthesis of forosamine
230
by Tietze and coworkers.
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