Industrial Biotransformations

Aminoacylase
Aspergillus niger
● The hydrolysis is performed by slow addition of hydroxide solution, maintaining the mixture
at pH 9–10; at this pH the initial product undergoes decarboxylation; this causes a reduction
in pH and, by careful control of the base addition, the resulting mixture can be kept approximately
neutral.
● The neutral solution can be directly used for the biotransformation.
● The product is extracted directly from the aqueous reaction mixture with methyl-tert-butyl
ether (MTBE) and is of high enantiomeric purity.
● The d-isomer can be recycled via an oxazolinone that tautomerizes to the enol:
N
1 = N-acetyl-3-(4-thiazolyl)alanine
2 = oxazolinone (azlactone)
3 = enol
Fig. 3.5.1.14 – 3
● Since the enzyme is immobilized and employed in a packed bed reactor it can be used several
times resulting in a protein-free solution after down-stream processing.
● The process can be applied to other unnatural alanine derivatives, e.g.:
Fig. 3.5.1.14 – 4
404
S
D-1
CO 2H
NHAc
1 = 2-naphthylalanine
2 = 4-cyanophenylalanine
3 = 2-pyridylalanine
4 = allylglycine
Ac 2O, OH -
N
N
S
S
2
N
N
3
O
OH
O
O
Me
Me
L-1 L-2
N NH2
L-3
NH2
CO2H
CO2H
NC
NH 2
L-4
NH2
N
CO2H
S
D,L-1
CO2H
EC 3.5.1.14
CO 2H
NHAc