Chemistry Reference
In-Depth Information
Novozym 435
vinyl acetate
p
OH
p
O
n
m
OH
OH
n
m
O
Scheme 14
Tuning of polymer properties by enantioselective enzymatic transesterification of
O
O
OR
O
X
O
A
O
Novozym 435
R-OH
+
O
B
O
O
O
A
B
O
O
R
O
O
Scheme 15
used for the enzymatic grafting of vinyl acetate, no reaction was observed over a
period of 24 h. In contrast, when a backbone containing 100%
-secondary al-
cohol groups was used, the enzymatic esterification of vinyl acetate occurred from
75% of the alcohol groups within 24 h. This is the first example in which chiral infor-
mation stored in a polymer chain can be “read out” by an enantioselective enzymatic
reaction.
In a related approach, Padovani et al. prepared copolymers of styrene and a
styrene derivative containing two pendant ester bonds using free-radical poly-
Novozym 435 as the catalyst and benzyl alcohol or (
rac
)-1-phenylethanol as the
nucleophile. Interestingly, the ester bond closest to the polymer backbone (posi-
98% to the corresponding benzyl ester. The transesterification was not only highly
chemoselective but also enantioselective. Conversion of (
rac
)-1-phenylethanol in
the transesterification reaction amounted to a maximum conversion of 47.9% of the
(
(
R
)
-alcohol, and only at the ester position B.
Yashima et al. showed an example where the polymer helicity was controlled
phenylacetylenes containing hydroxyl or ester groups were obtained by the kinetic
resolution of the corresponding racemic hydroxy-functional phenylacetylene (see
poly(phenylacetylene) with a high molecular weight
R
)
(
M
n
=
89 kDa; PDI
=
2
.
0
)
and
