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O
O
Sharpless
A
E
O
O
C
12
H
25
H
O
O
O
HO
CO
2
Me
OTBS
HO
O
C
12
H
25
20
21
22
C
12
H
25
C
12
H
25
allenylboronic acid
O
O
D-(-)-DIPT
OTBS
OMOM
HO
MOMO
23
14
O
O
( )
5
O
O
O
26
O
O
O
( )
5
O
( )
7
CO
2
Me
O
O
( )
5
24
25
O
27
OH
14
+
26
O
C
12
H
25
O
10
HO
(10
R
)-corossolin
O
HO
OH
14
+
27
O
C
12
H
25
O
10
HO
O
HO
(10
S
)-corossolin
Scheme 10-8. Total synthesis of (10R)- and (10S)-corossolin by Wu et al.
almost the same. Therefore, they could not judge which one should be the natural
product. In 1999, we also completed the synthesis of both C-10 isomers. The
rotation comparison of our samples showed that (10R)-corossolin
ð½
a
D
¼
19
:
1
Þ
was close to the natural product
ð½
a
D
¼
19
Þ
, whereas that of (10S)-corossolin
ð½
a
D
¼
24
:
6
Þ
is more different. In addition, NMR data of our synthetic (10R)-
corossolin was completely in accord with those of the natural one. So natural
corossolin should have a 10R configuration. By comparison with physical data
of known acetogenins, (10S)-corossolin was strongly suggested to be Howiicin C
isolated by Zhang et al. in 1993.
35
Our synthesis of corossolin started from the cheap sugar material, D-glucono-d-
lactone, whose C-3 and C-4 stereogenic centers were introduced into the target as
C-19 and C-20, respectively. Subsequent introduction of C-15 and C-16 was
achieved by Sharpless epoxidation of an allylic alcohol intermediate, and then
the THF core 14 was established through a couple steps of transformations. On
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