The enantiomeric recognition of chiral organic ammonium salts by chiral pyridino-macrocycles bearing aminoalcohol subunits

Pyridine-based macrocycles were prepared by treating 2,6-bis[[2′6′-bis(bromomethyl)-4′-methylphenoxy]methyl]pyridine 3 with the appropriate chiral aminoalcohols. The enantiomeric recognition of these macrocycles bearing aminoalcohol subunits of the pyridinocrown type ligand was evaluated for chiral organic ammonium salts by UV titration. The important differences were observed in the Ka values of (R)-Am2 and (S)-Am2 for (S,S,S)-1, (S,S,S)-2 and (S,S,S)-3 hosts, KS/KR = 5.0, KS/KR = 2.4 and KS/KR = 5.0, respectively. There seems to be a general tendency for hosts to recognise (S)-enantiomers for both Am1 and Am2.

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Macrocyclic (S,S,S)-1C43H66N4O5[α]D35=+6.8 (c 0.7, CH2Cl2)Source of chirality: l-leucineAbsolute configuration: (S,S,S)

Macrocyclic (S,S,S)-2C52H60N4O5[α]D35=+23.9 (c 0.7, CH2Cl2)Source of chirality: l-phenylalanineAbsolute configuration: (S,S,S)

Macrocyclic (S,S,S)-3C49H54N4O5[α]D35=-23.7 (c 0.7, CH2Cl2)Source of chirality: l-glycinolAbsolute configuration: (S,S,S)