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O
HO
O
O
11,12-Epoxy-
cembrene C (
28
)
(-)-7,8-Epoxy-
cembrene C (
33
)
(-)-13-Hydroxy-11,12-
Epoxy-neocembrene (
51
)
O
O
R
O
OH
(+)-3,4-Epoxy-
cembrene A (
56
)
(+)-11,12-Epoxy-
sarcophytol A (
181
)
R = CH
2
OH, Pseudoplexaurol (
182
)
R = CHO, Pseudoplexaural (
183
)
R = CO
2
Me, Pseudoplexauric acid
methyl ester (
184
)
Figure 6-10
Sarcophyton crassocaule and then isolated from the soft coral Eunicea spp.
15
in
1993 by Shin and Fenical. Although its chemical structure was characterized spec-
troscopically,
27
the absolute configuration of the epoxide moiety remains undeter-
mined so far. (
)-13-Hydroxy-11, 12-epoxyneocembrene (51), isolated in 1988 by
Suleimenova et al. from the soft coral Sarcophyton trocheliophorum, has been
shown to be an effective inductor of the release of labeled glucose from the
lecithincholesterol liposomes and to exhibit cytostatic activities.
104
It was charac-
terized spectroscopically. The absolute configuration of C-1 and C-13 has been
defined to be (1S,13S) by chemical transformation, but the absolute configuration
of the epoxide of 51 remains undetermined. (
þ
)-3,4-Epoxycembrene A (56), a
naturally occurring epoxy derivative of cembrane diterpene R-(
)-cembrene A
(59), was first isolated in 1981 by Bowden et al. from the Australian soft coral
Sinularia facile,
105
and it was subsequently found in various marine soft coral,
that is, Nephthea brassica (Formosan),
28
and Sarcophyton spp. The absolute con-
figuration of 56 was determined as (1R,3S,4S) by means of extensive spectroscopic
techniques and chemical degradation. And 56 has been shown to be a potent cyto-
toxic contituent against A549, HT29, KB, and P388 cell lines by Duh et al.
106,107
(
þ
)-11,12-Epoxysarcophytol A (181), an epoxy cembrane diterpene, was first iso-
lated by Bowden et al. in 1983 from an Australian marine soft coral Lobophytum
sp.
100
and characterized spectroscopically and chemically as (1Z,3E,7E)-14-hydro-
xyl-11,12-epoxy cembra-1,3,7-triene. The configuration of 14-hydroxyl was
confirmed as S by a zinc-copper couple-mediated reductive elimination of the epoxide
moiety leading to the formation of a known cembrane diterpenoid sarcophytol A (3), a
possible
biosynthesis
precursor
of
181.Howeve ,theabsolute
configuration
of
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