Synthesis of a novel class of carbohydrate-containing calix[4]resorcinarene adopting an asymmetrical diamond structure

摘要

A novel type of calixsugars, containing sugar moieties at the methine bridges of the calixarene is introduced. These calixsugars were prepared via a nonconvergent stepwise fragment condensation. Four new stereogenic centers were formed simultaneously, and only one diastereoisomer 5 was isolated. The condensation procedure is remarkably mild allowing for a large diversity of labile groups to be used. The solution structure of calixarene 5 with two D-glucose and two hexyl moieties was determined by NMR spectroscopy by means of NOEs and coupling constants for molecular dynamics (MD). Chemical shifts were used to validate the conformation with the least NOE and J violations. The structure of calixsugar 5 has the configuration rctc referring to one sugar residue (r = reference, c=cis, t = trans) and adopts a diamond conformation for the macrocyclic backbone with the two sugar moieties axial on opposite sides of the macrocyclic ring and the two hexyl groups on the same side.