Chirality in microcystins.

A new method has been developed to identify the isomers of amino acids by derivatization of the corresponding standards with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide (Marfey's reagent or FDAA) and analysis of the diastereomeric derivatives by a liquid chromatography-thermospray mass spectrometry technique. Quantification of the FDAA derivatives that originate from standards was possible by using L-phenylalanine as the internal standard. The procedure was applied to determine the chiralities of the amino acids present in some previously uncharacterized blue-green algal peptides (microcystins).