Conformational studies of per-O-trimethylsilyl derivatives of D-fructoses and oligosaccharides containing β-D-fructofuranose residues by 220- and 300-MHz P.M.R. spectroscopy

Abstract

The interpretation of 220- and 300-MHz P.M.R. spectra and the accurate chemical shifts and coupling constants of a number of per-O-trimethylsilyl-(TMS-)D -fructose derivatives and TMS-oligosaccharides containing beta-D-fructofuranose residues are presented. On the basis of calculations with an adapted Karplus equation it is concluded that TMS-alpha- and -beta-D-fructopyranose occur in the 2C5(D) chair conformation whereas the D-glucopyranose rings in the oligosaccharides adopt the usual 4C1(D) chair conformation. The structure of the latter units is very similar to that of TMS-alpha-D-glucopyranose. The 4E(D) envelope and 4T5(D) twist are the principal conformations of the D-fructofuranose rings. The conformation of the furanose ring depends on the number and kind of monosaccharide units attached thereto. The calculated, preferred conformation of the C-5-CH2OTMS group of the D-fructofuranose moieties correlates with the time-averaged displacement of C-4 above the plane of C-2, C-3, and O-5.