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710 Chapter 21
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b.
Recall that imine formation is best carried at a pH about 1.5 units lower than the p
K
a
of the protonated
ammonium ion (Section 16.8), that is, at about pH
=
8. Therefore, the carboxyl groups will be in their
basic forms. If reductive amination is carried out in the laboratory, both the d- and l-isomer (a racemic
mixture) of each amino acid will be formed.
+
O
O
O
_
pyruvic acid
1. NH
3
, trace acid
2. H
2
, Pd/C
O
O
_
alanine
NH
3
+
O
O
_
alanine
NH
3
+
O
O O
O
O
O
O NH
3
_
O
_
_
O
_
aspartate
oxaloacetic acid
+
+
1. NH
3
, trace acid
2. H
2
, Pd/C
O
O
O
O NH
3
_
_
aspartate
+
+
1. NH
3
, trace acid
2. H
2
, Pd/C
O
O
O
O
_
O
_
-ketoglutaric acid
O
O
O
O
_
_
glutamate
NH
3
+
O
O
O
O
_
_
glutamate
NH
3
+
22.
Notice that the R group attached to the Br is the same as the R group attached to the
a
-carbon of the amino
acid.
CHCOO
−
R
corresponds to
Br
R
NH
3
+
a.
leucine
b.
methionine
23.
As in Problem 22, the R group attached to the Br is the same as the R group attached to the
a
-carbon of the
desired amino acid.
a.
4-bromo-1-butanamine
b.
benzyl bromide
24.
Notice that the R group attached to the carbonyl group of the aldehyde is the same as the R group attached
to the
a
-carbon of the amino acid.
CHCOO
−
R
corresponds to
CH R
NH
3
+
O
a.
alanine
b.
isoleucine
c.
leucine