Biomedical Engineering Reference
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Ph
O
Ph
Ph
TMSO
233
Ph
231
O
OH
steps
TfOH (20 mol%)
+
BzO
CH
2
Cl
2
, -78°C, 15 h
85%
TMS
234
235
232
SCHEME 9.39
Synthesis of (
R
)-(+)-orizaterpenyl benzoate
235
by Tietze and coworkers.
(
R
)-(
þ
)-orizaterpenyl benzoate
235
[86]. Hence, reaction of ketone
231
with
allylsilanes
232
and
233
in the presence of a catalytic amount of TfOH led to
234
as the main product in a 9:1 ratio. Further manipulation of
234
gave the desired
compound
(Scheme 9.39).
Several new polyoxygenated cembrenes such as
235
have been isolated from
terrestrial and marine sources over the last years [87]. They all formally derive from
(
241
)-cembrene [88] and show anti-HIV activity, anti-inflammatory properties,
and neuro- and cytotoxicity [89]. For the enantioselective synthesis of
þ
, Tietze
et al. [90] used a similar facial-selective domino allylation/ether formation [91]
to that described for
241
235
to construct one of the tertiary alcohol moieties in
241
(Scheme 9.40). Here, the earlier developed norpseudoephedrine derivative
237
was
used. Thus, reaction of allylsilane
232
with ketones
236
and
237
led to homoallylic
ether
238
in a 95:5 selectivity. Further transformations of
238
afforded
240
via a
highly selective metathesis of
239
to form the 14-membered ring system present
in
241
.
(
is a metabolite of the marine dinoflagellate
Sym-
biodinium
sp [92]. Compounds of this type show low toxicity but strong effects on
osteoclast cells and they might be of interest in the development of antiosteoporosis
drugs [93]. In their synthesis of
242
, Maier and Varseev [94] used a domino Wittig-
Horner/cycloaddition process employing
243
and
244
as substrates. The obtained
product
þ
)-Neosymbioimine
242
246
, which is formed via the probable transition state
245
in 86% yield, was
further transformed to give
242
(Scheme 9.41).
O
O
CF
3
Ph
OTBDPS
NH
Ph
236
O
N
O
+
OTBDPS
TMSO
TMS
CF
3
238
237
232
O
OH
AcO
AcO
S
S
S
S
steps
O
OPMB
OPMB
HO
241
240
239
SCHEME 9.40
Synthesis of (+)-cembrene
241
by Tietze and coworkers.
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