( 13C)Substituted sucrose: 13C 1H and 13C 13C spin

Abstract

Sucrose (β- d-fructofuranosyl α- d-glucopyranoside, 1), methyl α- d-fructofuranoside ( 2), and methyl β- d-fructofuranoside ( 3) have been prepared by chemical and / or enzymic methods with single sites of 13C-substitution at C-1, C-2, C-3, and C-6 of the fructofuranosyl ring . 1H (500 MHz) and 13C (75 and 125 MHz) NMR spectra of 1–3 have been obtained, yielding 1H 1H, 13C 13C spin coupling constants that were used to assess furanose ring and glycoside bond conformations is aqueous ( 2H 2O) solution. Results show that the conformational mobility of the furanosyl ring in 3 is altered when incorporated into 1. Furthermore, 13C 13C and 13C 1H spin couplings across the glycosidic linkage suggest a ψ torsion angle different from that observed in the crystal (φ appears similar). Interplay between the strength of the exoanomeric effect and hydrogen bonding in solution may be responsible, in part, for the apparent conformational flexibility of 1. In addition, spin couplings in 2 and 3 have been compared to those measured previously in α- d- threo-pentulofuranose ( 4) and β- d- threo-pentulofuranose ( 5), respectively, as a means to study the effect of glycosidation and hydroxymethyl substitution on the solution conformation of the 2-ketofuranose ring. The conversion of 4 to 2 is accompanied by minimal conformational change, whereas a significant change accompanies the conversion of 5 to 3, showing that the effect of substitution on ring conformation depends highly on ring configuration before and after substitution.