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:
(1.24)(1.25)Acylation of amino acids with 5-dimethylami-
nonaphthalene-1-sulfonyl chloride (dansyl chlo-
ride, DANS-Cl) is of great analytical importance:
(1.26)The aryl sulfonyl derivatives are very stable
against acidic hydrolysis. Therefore, they are
suitable for the determination of free N-terminal
amino groups or freeε-amino groups of pep-
tides 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.(1.27)(1.28)1.2.4.2.2 AlkylationandArylation
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:(1.29)The N-methyl compound can also be formed by
methylating with HCHO/HCOOH the benzyli-
dene derivative of the amino acid, formed ini-
tially by reaction of the amino acid with ben-
zaldehyde. The benzyl group is then eliminated