A fast and simplein situ method for the determination of the absolute configuration of amino acid esters using the chiroptical properties of their Eu(FOD)3 complexes

Summary The NMR shift reagent, Europium(III)-tris-(1,1,1,2,2,3,3)-heptafluoro-7,7-dimethyl-4-6-octanedione Eu(fod)₃], complexes efficiently with-amino acid esters in chloroform. These complexes exhibit characteristic circular dichroism (CD) spectral patterns in the 350-250 nm region. A fast and simple procedure (also in microscale) has been worked out which utilizes the signs of these CD bands for the determination of the absolute configuration at the-carbon atomin situ. In the L-series, a positive CD band is observed at around 310 nm and a negative one in the 290-280 nm region. The CD spectra of the Eu complexes of the D-isomers are mirror images of those of the L-configurations. An empirical rule is proposed.Presented in part at the 2nd International Congress on Amino Acids and Analogues, Vienna, Austria, August 5–9, 1991.