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O
O
HO
HO
O
O
10
HO
HO
O
O
O
O
(TfO)
2
O
Bu
4
NBH
4
tBu
1
tBu
O
O
Me
Me
HO
HO
OH
OTf
O
O
O
O
GC
7-
O
-triflate GB
O
HO
O
HO
O
O
tBu
O
Me
HO
O
O
GB
During the structural studies of ginkgolides, several analogs were synthesized. The so-
called iso-ginkgolide derivatives, which stem from a translactonization of ring E, are of
particular interest. In 2002, an x-ray crystallographic structure of an iso- ginkgolide deri-
vative, 1,6,10-triacetate-isoGC, was obtained, and a mechanism for the formation of iso-
derivatives that includes opening of ring E, stabilization of the intermediate by hydrogen
bonding to 3-OH, and capture by acetic anhydride was suggested.
70
O
O
HO
AcO
O
O
10
10
HO
AcO
O
O
O
O
1
t
Bu
1
t
Bu
3
3
O
O
Me
7
Me
7
HO
6
AcO
HO
6
OH
O
O
O
O
GC
iso-ginkgolide
Base
Ac
2
O
O
O
HO
HO
O
O
10
10
HO
HO
O
O
O
O
1
1
t
Bu
t
Bu
3
3
O
O
Me
Me
7
7
6
O
HO
O
O
O
O
H
O
O
7.2
GINKGOLIDES AND THE PAF RECEPTOR
The first direct interaction of ginkgolides with an important biological target was
shown in 1985 when it was discovered that ginkgolides, particularly GB, are
antagonists of the PAF receptor.
71-73
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