A sulfonated calix[4]resorcinarene with l-pipecolinic acid groups as a water-soluble chiral NMR solvating agent

A water-soluble calix[4]resorcinarene containing l-pipecolinic acid groups is investigated as a chiral NMR solvating agent for aromatic-containing substrates. The substrates form complexes by insertion of the aromatic ring into the cavity of calix[4]resorcinarene. Compounds with phenyl, naphthyl, indole, indoline and pyridyl rings were investigated. The substrates also have ammonium or carboxylate functional groups. The effectiveness of the calix[4]resorcinarene with l-pipecolinic acid groups is compared to similar reagents with proline, hydroxyproline, and α-methylproline moieties that have previously been reported. The derivative with l-pipecolinic acid usually produces better enantiomeric discrimination compared to previous calix[4]resorcinarene reagents.

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2,8,14,20-Tetra(sodium propyl-1-sulfonate)-5,11,17,23-tetra(l-pipecolinylmethyl)calix[4]resorcinareneC64H80N4O28S4Na4[α]D20=-7.8 (c 1, H2O)Source of chirality: l-pipecolinic acidAbsolute configuration: (S,S,S,S)