New selenourea based chiral solvating agents for the enantiodiscrimination of amino acid derivatives

Two new bis-selenoureas BSDA and TFSDA, along with the urea TFUDA, were synthesized. BSDA was prepared by reacting acyl chloride with potassium selenocyanate, followed by the addition of (1S,2S)-1,2-bis(2-hydroxyphenyl)ethylenediamine (DA). TFSDA was obtained through a three steps process: first, the formation of the formamide, followed by the synthesis of the 3,5-bis(trifluoromethyl)phenyl isoselenocyanate and, finally, the reaction between the isoselenocyanate and the diamine. TFUDA was prepared by simply reacting DA with 3,5-bis(trifluoromethyl)phenyl isocyanate. The intermediates and the products were characterized by nuclear magnetic resonance (NMR) spectroscopy. Selenoureas and the urea were applied as chiral solvating agents (CSAs) for the differentiation of 1H and 19F NMR signals of the enantiomers of three kinds of amino acid derivatives: N-acetyl, N-3,5-dinitrobenzoyl, N-trifluoroacetyl. The enantiodiscrimination experiments were conducted on ternary mixtures CSA/amino acid derivative/DABCO (1:1:1) in CDCl3. DABCO was necessary to solubilize the amino acid derivatives. The chiral recognition processes were investigated by Rotating frame Overhauser Effect SpectroscopY (ROESY) experiments and by Diffusion-Ordered SpectroscopY (DOSY).