The derivative of aminophenyl-aldehyde with an asymmetric carbon and an uryl group, (S)-2, was synthesized. The combination of (S)-2 and aliquat-336 in CDCl3 extracted underivatized amino acids in water layer by imine formation with enantioselectivities of 12/1 for Phe, 13/1 for Val, and 12/1 for Leu, which are comparable with those of previously reported binaphthol-based extractor (S)-1. The enantioselectivities of (S)-2 is remarkable considering the low molecular weight compared to (S)-1. Density functional theory computations and experimental data demonstrate that imine bond is strengthened by resonance-assisted hydrogen bond with the nearby NH group.
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Acknowledgments. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (NO. NRF-2017 R1A2B2009672).
© 2018 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
- Amino acid
- Chiral extractor
- Liquid–liquid extraction