Environmental Engineering Reference
In-Depth Information
4.1 Possible Reactions of Amino Acids
Reactions, both chemical and enzymatic, involving amino acids have been exten-
sively reported in the literature though the context of such studies have concentrated
on the effects of amino acid conversion on nutrition, significance on physiologi-
cal behaviour and medicine and origins of life. Such studies were not reported as
a preparative method for the synthesis of those compounds. From these studies it
is apparent that a number of the products that are (or can be) produced are also
prepared industrially for various (technical) applications. For example in leucine
degradation in the mevalonate pathway, dimethylallyl pyrophosphate (DMAPP), a
pre-cursor to isoprene used in rubber manufacture, is formed. With the aid of the
enzyme isoprene synthase, found in the leaves of a number of tree species [26-28],
DMAPP may be converted to isoprene. Such observations are not limited to leucine
and indeed for a large majority of amino acids show interesting product formation
[22] including aspartic acid and arginine.
Acrylamide and acrylic acid are respectively synthesised by the hydroly-
sis reaction of acrylonitrile and the Reppe reaction using acetylene and are
used as monomers for the production of the corresponding polymeric materials
poly(acrylamide) and poly(acrylic acid) [29]. However, articles investigating the
formation of acrylamide in food products have described that Maillard reactions,
particularly in the presence of asparagine, had lead to the formation of acrylamide
[30-33] while others report the formation of acrylic acid from an aspartic acid path-
way [34]. Other reactions of aspartic acid are also known such as
-deamination
under elevated temperatures in the presence of water resulting in the formation
of fumaric and maleic acid [35]. Both these compounds have applications in the
formation of unsaturated polyesters. The
α
α
-decarboxylation to
β
-alanine has also
been reported [36]. Although
-alanine has somewhat limited use in its own right, it
does make a potentially interesting precursor for the synthesis of a number of other
compounds.
Diamines such as 1,6-hexanediamine (HMDA) and 1,4-butanediamine (BDA)
are produced by the chemical industry. In the case of BDA production is carried
out using reactions requiring propylene, ammonia and hydrocyanic acid. Diamines
are used in the synthesis of nylon engineering polymers such as nylon-6,6 and
nylon-4,6. Interestingly 1,4-butanediamine is the final product in arginine hydroly-
sis and decarboxylation (decomposition). Arginine is hydrolysed using the arginase
enzyme [37, 38] to ornithine (and urea) which can then undergo decarboxylation
resulting in formation of 1,4-butanediamine [39].
Based on the current knowledge as to possible reaction transformations of amino
acids coupled with an overview of products and processes of the chemical industry
one may envisage a synthetic scheme that leads to a number of interesting products,
Fig. 4.
Synthesis of industrial products starting from either arginine or aspartic acid
involves some hurdles to overcome. In the pathway A described above, it has
β
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