The fucofuranoside method, a new H-1 and C-13 nuclear magnetic resonance method to determine the absolute configuration of secondary alcohols

A new H-1 and C-13 NMR method for determining the absolute configuration of secondary alcohols, using their beta-D- and beta-L-fucofuranosides, has been devised. The conformations of the two enantiomeric furanosyl groups are symmetrical in the symmetrically substituted furanosides (Fig. 3), whereas they are unsymmetrical in the unsymmetrically substituted furanosides (Fig. 7). The Delta delta(H)(p) (H-1) and Delta delta(C)(p) (C-13) values (Fig. 4 and 6) were obtained by subtracting the chemical shifts, in pyridine-d(5), of the beta-D-isomer from the corresponding chemical shifts of the beta-L-isomer. The H-1 NMR analysis utilizes the strong anisotropy of the solvent which, solvated to the fucofuranosyl group, exerts uneven influences on the aglycon. The Delta delta(H)(p) values are positive for the protons of the right segment (R-r in Fig. 3), and negative for the protons of the left segment (R-I) In the C-13 NMR, the two glycosides experience glycosidation shifts in the opposite way. In the symmetrically substituted furanosides, the Delta delta(C)(p) values are positive for the right beta 7-carbon and negative for the left beta-carbon (Fig. 6, la,b and 6a,b). In the unsymmetrically substituted furanosides, the Delta delta(C)(p) values of the anomeric, alpha- and the left beta-carbons of the (S)-type beta-fucofuranosides (2a,b and 3a,b) are negative. In contrast, the Delta delta(C)(p) values of the anomeric, alpha- and the right beta-carbons of the (R)-type beta-fucofuranosides (4a,b and 5a,b) are positive. A similar Delta delta(C)(p) pattern was shown to exist in the beta-D- and beta-L-glucopyranosides (Fig. 8), and even in the beta-D- and alpha-D-glucopyranosides (Fig. 10). (C) 1997 Elsevier Science Ltd.