Chemistry Reference
In-Depth Information
H
H
H
O
O
O
phosphate buffer
O
O
O
lipase (Amano PS)
H
H
H
OCOC
3
H
7
OH
OH
racemic
racemic
ee > 99%
Scheme 6
O
Cl
N
MeO
R
O
N
Hon
43
avenaciolide
N
O
N
NH
2
O
O
OH
O
OH
O
Ol iv o
41
(-) -
homo
Carbovir
1
R
OH
O
O
O
D
IBAL-
H
O
O
OH
O
HO
O
OH
Roberts
32b
: (+)-BrefeldinA
OH
2
OH
LiAlH
4
R
OH
OH
OH
Pd
HO
4
OH
O
OH
3
O
N
t-Bu
OH
OH
Carba nucleosides
N
HO
HO
N
Rhee
36
(1S, 2R)-guanine
analogues
O
NH
HN
Rhee
37
(-)
carbaguanine
H
2
N
HO
N
OH
O
N
N
O
Roberts
36
Mevinic acid
HO
OO
N
N
HOOC
O
NH
2
HO
O
NH
2
HO
OH
OH
NH
N
N
Aggarwal
44
polyoxin C
To yo ta
38
(+/-)-epinor-BCA
HO
Grieco
40
(+ /-)-sesbanimide A
O
HO
N
N
O
OTMD
N
Fourrey
39
carba DNA
NH
Roberts
35
(-) - c a r b o v i r
HO
N
N
NH
2
P
N
CN
O
Scheme 7
Concerning the asymmetric approach, Jorgensen has published a
series of articles dealing with the use of copper(II) bisoxazoline as
asymmetric catalyst of the HDAR
27
and the ene-reaction
28
with glyoxylate
esters. In the presence of cyclopentadiene, ethyl glyoxylate led with a high
endoselectivity to a single cycloadduct with an ee of 60% (72% yield). The
rearrangement was induced by the alkaline hydrolysis of the compound
and the (-)-a-hydroxy-g-lactone was finally obtained with an ee of 99.5%
after recrystallisation. This method appeared superior to the enzymatic
resolution because of the complete endoselectivity.
Finally, the a-hydroxy-g-lactones could be obtained optically pure, by
esterification with acetyllactyl chloride and the resulting acetyllactyl
derivatives were separated.
29
Recently, a kinetic resolution of the a-
hydroxy-g-lactones has been described by Shiina,
30
using an asymmetric
acyl-transfert catalyst ((R)-BTM) in the presence of an acetylating agent.
Search WWH ::
Custom Search