Industrial Biotransformations

3.13 Amino Acids
In general, most of these approaches have been demonstrated on a practical scale and
many of the enzymes are commercially available. A variety of amino acids can also be
prepared enzymatically from b-chloroalanine [29].
Several dynamic resolution approaches have been reported for the synthesis of amino
acids. For example, the wrong enantiomeric amino ester can be epimerized by forming a
Schiff-base with pyridoxal-5-phosphate or some other aldehydes [36].
R
O
NH 2
OR'
R = alkyl, aryl
hydrolases
R
pyridoxal-5-phosphate
Lipase-catalyzed dynamic resolution of oxazolin-5-ones can also be accomplished successfully,
as the a-proton is sufficiently acidic for in situ racemization. In this particular
case, both enantiomers can be produced depending on the lipases used [37].
R
N
O
O
Ph
R = alkyl, aryl
pH 7.6
lipase A
lipase B
HN
Ph
HN
Ph
O
NH2
COOH
O
COOH
O
OH
L-form
D-form
Similar approaches have been developed for hydantoins and thiazoline derivatives [38].
The use of a hydantoin racemase for dynamic resolution has also been reported [39].
+
+
+
R
R
R
O
NH2
N
N
O
OR'
O
Ph
O
O
Ph
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