Chromatographic determination of L- and D-amino acids in plants.

Quantities of free L- and D-amino acids (L- and D-AAs) in plants (leaves of coniferous and decidious trees, fleshy fruits, leaf blades of fodder grasses, and seeds and seedlings of edible legumes) were determined. Amino acid (AA) enantiomers were converted into diastereomers using pre-column derivatization with o-phthaldialdehyde together with N-isobutyryl-L(or D)-cysteine followed by separation of the resulting fluorescent isoindol derivatives on an octadecylsilyl stationary phase using high-performance liquid chromatography. Relative amounts of D-AAs were also determined by enantioselective gas chromatography-mass spectrometry on Chirasil-L-Val. Free D-AAs acids in the range of about 0.2% up to 8% relative to the corresponding L-AAs acids were found in plants. D-Asp, D-Asn, D-Glu, D-Gln, D-Ser and D-Ala could be detected in most of the plants, and D-Pro, D-Val, D-Leu and D-Lys in certain plants. As D-AAs were detected in gymnosperms as well as mono- and dicotyledonous angiosperms of major plant families it is concluded that free D-AAs in the low percentage range are principle constituents of plants.

Liquid chromatographic determination of D- and L-amino acids by derivatization with o-phthaldialdehyde and N-isobutyryl-L-cysteine. Applications with reference to the analysis of peptidic antibiotics, toxins, drugs and pharmaceutically used amino acids.

In order to evaluate and extend the applicability of an analytical method that enables the quantitative and simultaneous high-performance liquid chromatographic determination of D- and L-amino acids (DL-AAs) by automated precolumn derivatization with o-phthaldialdehyde together with the chiral thiol N-isobutyryl-L-cysteine [J. Chromatogr., 666 (1994) 259] selected natural and synthetic bioactive peptides, as well as pharmaceutically used formulations of AA, were investigated and the amounts of D- and L-AA determined by fluorescence detection. Peptides containing cys(e)ine were oxidized with performic acid prior to hydrolysis with 6 M HCl, and those containing Trp were hydrolyzed with 4 M methanesulfonic acid (24 h at 110 degrees C in both cases). Peptides analyzed were the peptide antibiotics bacitracin, gramicidins A and S, polymyxin B, metanicin C, the peptide toxin malformin A and the peptide drugs D-Arg-[Hyp3,Thi5,8,D-Phe7]-bradykinin, beta-casomorphin and alpha s1-exorphin. Further, the enantiomeric ratios of pharmaceutically used AA formulations containing racemic DL-Ser, DL-Asp and DL-Met were determined, and the AA drugs L-Asp and L-Trp were tested negatively for the presence of the respective D-enantiomers. In two aqueous formulations of L-AA used for parenteral nutrition, low amounts of D-AA (0.1-0.9% with respect to certain L-AA enantiomers and of totally 128 mg and 149 mg D-AAs per liter infusion solution) were determined.