Secondary isotope multiplet nuclear magnetic resonance spectroscopy of partially labelled entities (SIMPLE): 13C spectra of stachyose and its subunits

Abstract

¹³ C N.m.r. measurements have been made, in (C²H₃)₂SO solutions, of some carbohydrates (sucrose, raffinose, melezitose, and stachyose) in which exchangeable protons have been partially deuteriated (ca.50:50). Signals from a single carbon atom type are observed as a series of multiplets (singlets to octests, at least) resulting from observation of different isotopomers measured under conditions of slow exchange. The multiplets are analysed in terms of the two-bond (β) and three-bond (γ) isotope effects that contribute to the deuterium-induced secondary isotope shift. Magnitudes of β and γ effects vary, giving rise to characteristic multiplets which have been used to check the assignment of the disaccharide sucrose, and to provide the assignment of the ¹³C n.m.r. spectra of the trisaccharides raffinose and melezitose and the tetrasaccharide stachyose in (C²H₃)₂SO solutions and in ²H₂O solutions by using mixed-solvent studies. The SIMPLE n.m.r. method may be used to provide information on the composition, substitution, and glycosidic linkages of oligosaccharides in solution.