The effect of substituents on the chiral solvating properties of (S)-1,6-dialkylpiperazine-2,5-diones
作者:Črt Malavašič、Branko Stanovnik、Jernej Wagger、Jurij Svete
DOI:10.1016/j.tetasy.2011.07.019
日期:2011.6
The effect of substituents on the chiral solvating properties of 13 different (S)-1,6-dialkylpiperazine-2,5-diones (S)-1a-m and five (35,6S)-1,3,6-trialkyl analogues (S,S)-1n-r was studied by NMR in CDCl(3) with methyl (RS)-N-benzoylleucinate (RS)-2a as the model analyte. Most diketopiperazines exhibited typical resolution, Delta Delta delta(-20)(RS) similar to 0.1 ppm. Increased performance was observed with 6-CH(2)R substituted compounds (S)-1h-j. The best resolution of the NH protons of (R)-2a and (S)-2a, Delta Delta delta(-2)(RS)0 = 0.227 ppm, was obtained with (S)-1-isopropyl-6-(4-nitrobenzyl)piperazine-2,5-dione (S)-1j. An additional syn-oriented substituent at the C(3) position decreased the enantioselectivity. Association constants for the binding of (S)-1j to each enantiomer of (RS)-2a in CDCl(3) at -20 degrees C were determined by NMR titration. (C) 2011 Elsevier Ltd. All rights reserved.