First enantiopure calix[6]aza-cryptand: synthesis and chiral recognition properties towards neutral molecules

The synthesis of the first enantiopure calix[6]aza-cryptand was achieved in five steps from the known 1,3,5-tris-O-methylated calix[6]arene. A 1H NMR spectroscopic study has shown that the chiral tren cap constrains the calixarene core in a straight cone conformation ideal for host–guest chemistry applications. As a result, the tetra-protonated derivative displays remarkable host properties towards polar neutral molecules and enantioselective recognition processes have been evidenced with chiral guests.

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(S)-(+)-2-Methyl-1-(2-nitrophenylsulfonyl)aziridineC9H10N2O4S[α]D20=+109 (c 0.7, CHCl3)Source of chirality: (S)-2-aminopropan-1-olAbsolute configuration: S

(S)-(+)-N2-2-Nitrobenzenesulfonyl-N1,N1-bis-[2-(2-nitrobenzenesulfonyl)amino-ethyl]-propane-1,2-diamineC25H29N7O12S3[α]D20=+56 (c 0.3, CDCl3)Source of chirality: (S)-2-aminopropan-1-olAbsolute configuration: S

C100H125N7O18S3[α]D20=+44 (c 0.3, CHCl3)Source of chirality: (S)-2-aminopropan-1-olAbsolute configuration: S

C82H116N4O6[α]D20=+16 (c 0.5, CHCl3)Source of chirality: (S)-2-aminopropan-1-olAbsolute configuration: S