Facile preparation of a symmetric hexavalent oleanolic acid/per-O-methylated α-cyclodextrin conjugate with two conformations in solution and unambiguous NMR analysis

A newly synthesized hexavalent oleanolic acid/per- O -methylated α -cyclodextrin conjugate shows significant differences in NMR spectra with previously synthesized analogs. Characterization of the product by 1 H NMR, 13 C NMR, COSY, HSQC , HMBC , TOCSY , NOE, and ROESY experiments were performed. Detailed investigations revealed that the compound has two conformations in solution and the ratio of them was 1:1. Further variable-temperature NMR study revealed that the two conformations were stable at temperature range of 273–323 K in CDCl 3 solution.