• ELSEVIER Carbohydrate Research 259 (1994)277-282 CARBOHYDRATE RESEARCH Note l3C_I" Spin-coupling constants in carbohydrates: magnitude and sign determinations via 2D NMR methods Anthony S. Serianni *, Carol A. Podlasek Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 (USA) (Received October 25th, 1993; accepted January 24th, 1994) Key words: 2D NMR; TOCSY; Spin-spin coupling; Conformational analysis; 13C Labeling Conformational analysis of carbohydrates has depended, in large part, on the use of three-bond (vicinal) IH_1H spin-coupling constants (31HH)' whose magni- tudes can be correlated with molecular torsion angles, as first enunciated by Karplus [1]. In the ensuing years, more sophisticated Karplus relationships have been advanced that account for substitution and/or electronegativity effects along H-C-C-H coupling pathways [2]. The relative ease of measurement of 3 1HH compared to other potentially useful coupling constants within carbohydrates (e.g., lCH and lee) is largely responsible for their dominant role in structure determina- tion. However, in some situations, 3 1HH are not available to probe the conforma- tional features of these molecules. A well-known example of this problem involves the assessment of O-glycoside linkage conformation in oligosaccharides where only 13C_l H and 13 C_ 13C spin-couplings are available for evaluating the phi (4)) and psi (l/1) torsion angles [3a-e]. Other situations, such as the presence of conformational averaging in solution, demand access to as large a parameter pool as possible in order to provide sufficient data on which to confirm or discard potential conforma- tional models. An example of the latter is found in structural studies of furanosyl rings [4], either as free entities or as components of more complex biologically important structures (e.g., polysaccharides, RNA, and DNA). Seminal work by Perlin and co-workers [5] and Pedersen and co-workers [6] has attempted to define the effect of carbohydrate structure on one- (llCH)' two- elCH) and three- elCH) bond 13C_1H spin-couplings. Karplus relationships have been proposed for C-C-C-H and C-O-C-H coupling pathways [5a,?]. In con- trast, 2 1CCH have been used less frequently as conformational probes, although *' Corresponding author. 0008-6215/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDl 0008-6215(94)00044-G