Conformational studies on pertrimethylsilyl derivatives of some 6-deoxyaldohexopyranoses and of four less-common aldohexopyranoses by 220-MHz P.M.R. spectroscopy : Substituent and configurational effects on the chemical shifts of the ring protons

Abstract

The complete interpretation of 220-MHz p.m.r. spectra and the accurate chemical shifts and coupling constants, obtained after computer simulation of the spectra, of the per-O-trimethylsilyl (Me3Si) derivatives of a number of 6-deoxy-aldohexopyranoses and of beta-D-altro-, beta-D-allo-, and alpha- and beta-D-talo-pyranose are given. By means of an adapted Karplus equation, the structure of the derivatives has been studied in detail. All of the pyranoid rings occur in the 4C1(D) or 1C4(L) chair conformation. The preferred conformation of the C-5—CH2OSiMe3 group in the four aldohexopyranoses was found to be dependent on the configuration at C-4. By comparison of Me3Si-aldohexopyranoses with the corresponding 6-deoxy analogues, it was found that the 6-OSiMe3 group has no marked effect on the conformation of thering. The influence of this group on the chemical shifts of the ring protons is discussed in terms of electric field and inductive effects. Rules are presented for the estimation of the chemical shifts of the ring protons of Me3Si-aldohexopyranoses and Me3Si-6-deoxyaldohexopyranoses.