Facile determination of absolute configurations of α -hydroxy acids by the expansion of Marfey's method

α-Hydroxy acids are often biosynthetically incorporated in natural small molecules such as depsipeptides from nonribosomal peptide synthetase pathways. While the absolute configurations of α-amino acids are conveniently determined by the LC/MS-based analysis of Marfey's derivatives of amino acids, the current methods to determine the absolute configurations of corresponding α-hydroxy acids require more complicated steps. So we expanded Marfey's method and developed a facile procedure determining the absolute configurations of α-hydroxy acids. The method was evaluated with the LC/MS analysis of the reaction products of various l,d-α-hydroxy acids coupled with Marfey's reagent (l-FDAA). This new method is operationally simple and applicable at a submilligram scale without any purification of the reaction mixture. We applied this facile procedure to a natural depsipeptide, zygosporamide, which bears l-phenylalanine, l,d-leucine, and l-leucic acid, and successfully determined the absolute configurations of its α-amino acids and α-hydroxy acid simultaneously. We believe that our approach may be practically useful for natural product chemists.