32 1 Amino Acids, Peptides, Proteins
industrial processes for a number of amino
acids.
1.2.5.1 GlutamicAcid..........................................
Acrylnitrile is catalytically formylated with
CO/H 2 and the resultant aldehyde is transformed
through aStreckerreaction into glutamic acid
dinitrile which yieldsD,L-glutamic acid after
alkaline hydrolysis. Separation of the racemate
is achieved by preferential crystallization of
theL-form from an oversaturated solution after
seeding withL-glutamic acid:
(1.60)A fermentation procedure with various selected
strains of microorganisms (Brevibacterium
flavum, Brev. roseum, Brev. saccharolyticum)
providesL-glutamic acid in yields of 50 g/lof
fermentation liquid:
(1.61)1.2.5.2 AsparticAcid...........................................
Aspartic acid is obtained in 90% yield from fu-
maric acid by using the aspartase enzyme:
(1.62)1.2.5.3 Lysine.................................................
A synthetic procedure starts with caprolactam,
which possesses all the required structural fea-
tures, except for theα-amino group which is in-
troduced in several steps:(1.63)Separation of isomers is done at theα-amino
caprolactam (Acl) step through the sparingly sol-
uble salt of theL-component withL-pyrrolidone
carboxylic acid (Pyg):(1.64)More elegant is selective hydrolysis of the
L-enantiomer by anL-α-amino-ε-caprolactamase
which occurs in several yeasts, for example
in Cryptococcus laurentii. The racemiza-
tion of the remaining D-isomers is possible
with a racemase of Achromobacter obae.
The process can be performed as a one-step
reaction: the racemic aminocaprolactam is
incubated with intact cells of C. laurentii
and A. obae, producing almost 100% L-
lysine.
In another procedure, acrylnitrile and ethanal
react to yield cyanobutyraldehyde which is
then transformed by a Bucherer reaction
into cyanopropylhydantoin. Catalytic hy-
drogenation of the nitrile group, followed
by alkaline hydrolysis yields D,L-lysine.