Amino acid formamidene butyl
esters are optimally prepared by heating
amino acids with
dimethylformamide dimethylacetal (
DMF-DMA) for 2 minutes at 65 degrees C and then with
n-butanol/
hydrogen chloride for 15 minutes at 65 degrees C. The formamidene butyl
esters of simple alpha-
amino acids and beta-
amino acids afford between 1.1 and 20 times the signal intensity of the corresponding butyl
esters during electrospray ionization tandem mass spectral analysis. Complex alpha-
amino acids, such as
ornithine,
arginine and
citrulline, and gamma-
amino acids are better analyzed as butyl
esters. Secondary alpha-
amino acids, such as
proline and
sarcosine, give a mixture of two iminium
salts with the
DMF-DMA derivatization method. A derivative incorporating two molecules of the
amino acid predominates at higher derivatization temperatures. Contrary to a previous report, N-formylamino
acids were not detected. The presence of
secondary amino acids in
amino acid mixtures, derivatized as formamidene butyl
esters, affords derivatives that incorporate two different
amino acids. The new formamidene butylation method is unlikely to replace the butylation procedure used by neonatal blood spot screening programs for
amino acid disorders, since a much poorer response was obtained with formamidene butyl
esters of
arginine and
citrulline, important in the diagnosis of
arginase deficiency and citrullinaemia.