Chemistry Reference
In-Depth Information
Recombinant
whole-cell catalyst,
containing:
racemase,
L-hydantoinase,
L-carbamoylase
O
rac
NH
2
N
HN
NH
N
CO
2
H
+2 H
2
O
-CO
2
-NH
3
O
(
S
)-
79
rac
-
78
Scheme 6.30.
O
1. Alcalase,
pH 8.0
2. 6N HCl
Ph
Lipase from
Mucor miehei
Ph
NH
NH
2
N
H
3
C
H
3
C
H
3
C
H
3
C
O
CO
2
n
-Bu
CO
2
H
H
3
C
H
3
C
n
-BuOH,
NEt
3
,
to luen e
3. Aberlite
IRA-67
(free base)
CH
3
CH
3
O
CH
3
(
S
)-
81
94% yield
99.5% ee
(
S
)-
82
44% yield
99.5% ee
(
S
)-
80
In situ
racemization
Ph
N
O
H
3
C
H
3
C
O
CH
3
(
R
)-
80
Scheme 6.31.
of substrate
80
due to easy racemization of azlactones under conditions of lipase-cata-
lyzed resolution via azlactone ring opening with an alcohol (Scheme 6.31) [109,110].
Using this resolution concept,
N
- benzoyl L -
tert
- leucine butyl ester, (
S
) -
81
, has been
synthesized with 94% yield and with 99.5% ee in the presence of a lipase from
Mucor
miehei
. The ring-opening reaction has to be carried out in a nonaqueous system due to
a competing nonenzymatic ring opening of the azlactone with water. The product (
S
) -
81
was converted into L-
tert
- leucine, (
S
) -
82
, via chemoenzymatic two-step hydrolysis (alca-
lase, pH 8.0, followed by 6 N HCl, refl ux) and subsequent neutralization of the hydro-
chloride of (
S
) -
82
.
A further class of hydrolases used in the resolution of amino acid precursors are
lactamases. In the presence of an
α
- amino -
ε
- caprolactam hydrolase (ACL - hydrolase),
racemic 3 -
-caprolactam was enantioselectively hydrolyzed under the forma-
tion of enantiomerically pure L-lysine [111]. Notably, this enzymatic resolution step was
coupled with an
in situ
racemization of the substrate by means of an ACL-racemase.
The resulting dynamic kinetic resolution proceeds with a high substrate input of 100 g/L
α
- amino -
ε
