Synthesis of new chiral imidazolium salts derived from amino acids: their evaluation in chiral molecular recognition

A family of new imidazolium salts derived from natural amino acids has been synthesized and tested for NMR enantiodiscrimination, as chiral shift reagents, of carboxylic acids. These imidazolium receptors contain different structural modifications and the splitting of the signals of the acids, after addition of the corresponding CSRs, depends on these structural variables. Compound 8b exhibited the strongest chiral solvating properties for racemic Mosher acid and was recognized as a suitable CSR for the determination of its enantiomeric composition.

Figure optionsDownload as PowerPoint slide

(S)-1-Benzyl-3-(1′hydroxy-1′diphenyl-4′-methyl-2′-pentanyl)imidazolium hexafluoroantimonideC28H31F6N2OSb[α]D20=+99.8 (c0.009,CH3OH)Source of chirality: l-isoleucineAbsolute configuration: (S)

(S)-1-Benzyl-3-(1′hydroxy-1′diphenyl-3′phenyl-2′-propanyl)imidazolium hexafluoroantimonideC31H29F6N2OSb[α]D20=+35 (c 0.010,CH3OH)Source of chirality: l-phenylalanineAbsolute configuration: (S)

(S)-1-Benzyl-3-(1′-hydroxy-1′-diphenyl-2′-propanyl)imidazolium triflamideC33H29F6N3O5S2[α]D20=+41.4 (c 0.004,CH3OH)Source of chirality: l-phenylalanineAbsolute configuration: (S)

(S)-1-Benzyl-3-(1′-hydroxy-1′-diphenyl-3′-methyl-2′-butanyl)imidazolium triflamideC29H29F6N3O5S2[α]D20=+46.9 (c 0.011,CH3OH)Source of chirality: l-valineAbsolute configuration: (S)

(S)-1-(1′naphthyl)-methyl-3-(1′-hydroxy-1′diphenyl-3′-phenyl-2′-propanyl)imidazolium triflamideC37H31F6N3O5S2[α]D20=+27.4 (c 0.005,CH3OH)Source of chirality: l-phenylalanineAbsolute configuration: (S)

(S)-1-(1′-naphthyl)-methyl-3-(1′-hydroxy-1′-diphenyl-3′-methyl-2′-butanyl)imidazolium triflamideC33H31F6N3O5S2[α]D20=+74.7 (c 0.011,CH3OH)Source of chirality: l-valineAbsolute configuration: (S)