NMR Spectral Assignment of Per-substituted Key-Intermediates of deta-Cyclodextrin and Implications in the Structures of the Derivatives

摘要

The compounds,6-per -O-(t-butyldimethylsilyl)-deta-cyclodextrin(1),2,3-per-O-benzyl-6-per-O-(t-butyldethylsilyl)-deta-cyclodextrin (2), 2,3-per-O-benxyl-beta-cyclodextrin (3),2,3,6-per-O-benxyl-deta-cyclodextrin(4),2,3,6-per-O-benxoyl-deta-cyclodextrin (5),are used as key intermediates in the synthesis of selectively substituted deta-CD derivatives.Simple and assignable ~1H and ~13C NMR spectra (chemical shifts and coupling constants)were obtained for compounds 1-4 indicating C_7 symmetry,~4C_1 glucose conformawtion and major gg arrangenent of H6,H6' atoms at the primary side.The erivative 5,however,gave very broad peaks at room temperature.The peaks could partially be assigned at 270 K,but the broadening was still present at 220 K.This implies that there exist several conformers of similar energy and C_1symmetry that continuously interchange,Since there is not a single type of stabilizing interaction that predominates.We attributed this phenomenon to the presence of the carbonyl group,which probably disfavors pi-pi stacking and induces random arrangements of the aromatic rings.