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PO(OEt)
2
CO
2
Et
PO(OEt)
2
CO
2
Et
a
O
c
185
186
b
OH
OTHP
O
137
187
OTHP
CHO
O
OTHP
d
e
f
CO
2
Et
O
CO
2
Et
CO
2
Et
O
188
189
190
g
h
i
O
CO
2
R
CH
2
OH
CH
2
OH
191
R = Et
192
R = H
193
194
O
33
Reagents and Conditions: (a) i. NBS, THF-water, 0
C; ii. K
2
CO
3
, MeOH, 72%; (b) i. DHP, p-TsOH,
CH
2
Cl
2
, rt; ii. O
3
,Py,CH
2
Cl
2
,
78
C, 61%; (c) LDA,
78
C, 30 min then aldehyde 187,
78
C
23
C., 61%; (d) LiClO
4
,C
6
H
6
,reflux, 75%; (e) i. p-TsOH, MeOH, 23
C; ii. MnO
2
, n-Hexane, 23
C,
71%; (f) TiCl
4
, Zn, THF, reflux, 42%; (g) i. KOH, EtOH-H
2
O, reflux, 90%; ii. LiAlH
4
,Et
2
O, 23
C, 90%;
(h) Ti(O
i
Pr)
4
, L-(
þ
)-DET, t-BuOOH, 20
C, 92%; (i) i. Ph
3
P, I
2
, imidazole, Py, Et
2
O-CH
3
CN (3:1), 0
C;
ii. NaBH
3
CN, HMPA, THF, 60
C, 80%.
Scheme 6-20
the epoxide of 181 remains undetermined and was assumed as (11S,12S) by the
authors. Pseudoplexaurol (182), a novel cembrenoid, was first isolated from the
Caribbean gorgonian Pseudoplexaura porosa by Rodr´guez and Mart´nez in
1993.
108
Although the chemical structure of 182 was characterized on the basis
of spectral data and chemical degradation, the relative as well as the absolute con-
figurations of three stereogenic centers (C-1, C-3, and C-4) remained to be assigned
unambiguously. And 182 has been shown to exhibit significant cytotoxic antitumor
activities against several human tumor cell lines. Pseudoplexaural (183) and pseu-
doplexauric acid methyl ester (184)
109
have also been found in other Caribbean
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