2009_Book_FoodChemistry

18 1 Amino Acids, Peptides, Proteins
These are highly reactive intermediary products
which form a mesomerically stabilized anion.
The anion can then react, for example, with
aldehydes. This reaction is utilized in amino acid
synthesis with glycine azlactone as a starting
compound:
The aryl sulfonyl derivatives are very stable
against acidic hydrolysis. Therefore, they are
suitable for the determination of free N-terminal
amino groups or free ε-amino groups of peptides
or proteins. Dansyl derivatives which
fluoresce in UV-light have a detection limit in
the nanomole range, which is lower than that of
2,4-dinitrophenyl derivatives by a factor of 100.
Dimethylaminoazobenzenesulfonylchloride
(DABS-Cl) and 9-fluoroenylmethylchloroformate
(FMOC) detect amino acids (cf. Formula 1.27
and 1.28) including proline and hydroxyproline.
The fluorescent derivatives can be quantitatively
determined after HPLC separation.
(1.24)
(1.27)
(1.28)
(1.25)
Acylation of amino acids with 5-dimethylaminonaphthalene-1-sulfonyl
chloride (dansyl chloride,
DANS-Cl) is of great analytical importance:
1.2.4.2.2 Alkylation and Arylation
N-methyl amino acids are obtained by reaction
of the N-tosyl derivative of the amino acid with
methyl iodide, followed by removal of the tosyl
substituent with HBr:
(1.26)
(1.29)
The N-methyl compound can also be formed by
methylating with HCHO/HCOOH the benzylidene
derivative of the amino acid, formed initially
by reaction of the amino acid with benzaldehyde.
The benzyl group is then eliminated