Visual enantiomeric recognition of amino acid derivatives in protic solvents

Article abstract of DOI:10.1021/jo050387u

Various types of chiral host molecules 2-7 based on a phenolphthalein skeleton and two crown ethers were prepared for use in visual enantiomeric recognition, and we examined their enantioselective coloration in complexation with chiral amino acid derivatives 9-22 in methanol solution. Methyl-substituted host (S,S,S,S)-S showed particularly prominent enantiomer selectivity for the alanine amide derivatives 11 and 12. A combination of methyl-substituted host (S,S,S,S)-S with guest (R)-11 or (R)-12 developed a purple color, whereas no color development was observed with (S)-11 or (S)-12. On the other hand, phenyl-substituted host (S,S,S,S)-6 showed deeper coloration with a wide range of (S)-β-amino alcohols compared to that seen with host (S,S,S,S)-6 and the corresponding (R)-β-amino alcohols at 0°C. Furthermore, absorbance inversion temperatures (AIT) were observed within the range of 0-50°C in many cases.