The Fucofuranoside Method, a New 1 H and 13 C Nuclear Magnetic Resonance Method to Determine the Absolute Configuration of Secondary Alcohols

Abstract

Abstract A new 1 H and 13 C NMR method for determining the absolute configuration of secondary alcohols, using their β-D- and β-L-fucofuranosides, has been devised. The conformations of the two enantiomeric furanosyl groups are symmetrical in the symmetrically substituted furanosides ( Fig. 3 Download high-res image (30KB) Download full-size image Fig. 3 . Front view of the presumed conformation of the glycosidic linkages of β- d -fucofuranoside ( A ) and β- l -fucofuranoside ( B ). ), whereas they are unsymmetrical in the unsymmetrically substituted furanosides ( Fig. 7 Download high-res image (39KB) Download full-size image Fig. 7 . Front view of the unsymmetrical conformations of the glycosidic linkages of the β- d - ( 2a , φ = +55°, ψ = −10°) and β- l -fucofuranoside ( 2b , φ = −55°, ψ = −20°) of the ( S )-type secondary alcohol 2 . ). The Δδ H p ( 1 H) and Δδ C p ( 13 C) values ( Fig. 4 Download high-res image (171KB) Download full-size image Fig. 4 . The Δδ H p values observed for the protons of the β- d - and β- l -fucofuranoside derivatives of the chiral secondary alcohols 1 to 7 (400 MHz, in ppm). Fig. 6 Download high-res image (131KB) Download full-size image Fig. 6 . The Δδ C p and Δδ C c (in parenthesis) values observed for the anomeric (C-1′) and aglycon carbons of the β-D- and β-L-fucofuranoside derivatives of the chiral secondary alcohols 1 to 7 (100 MHZ, in ppm). ) were obtained by subtracting the chemical shifts, in pyridine- d 5 , of the β-D-isomer from the corresponding chemical shifts of the β-L-isomer. The 1 H NMR analysis utilizes the strong anisotropy of the solvent which, solvated to the fucofuranosyl group, exerts uneven influences on the aglycon. The Δδ 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 1 ). In the 13 C NMR, the two glycosides experience glycosidation shifts in the opposite way. In the symmetrically substituted furanosides, the Δδ C p values are positive for the right β-carbon and negative for the left β-carbon ( Fig. 6 , 1a,b and 6a,b ). In the unsymmetrically substituted furanosides, the Δδ C p values of the anomeric, α- and the left β-carbons of the ( S ) -type β-fucofuranosides ( 2a,b and 3a,b ) are negative. In contrast, the Δδ C p values of the anomeric, α- and the right β-carbons of the ( R ) -type β-fucofuranosides ( 4a,b and 5a,b ) are positive. A similar Δδ C p pattern was shown to exist in the β-D- and β-L-glucopyranosides ( Fig. 8 Download high-res image (30KB) Download full-size image Fig. 8 . The Δδ C p values (in ppm) obtained for the anomeric (C-1′) and aglycon carbons, by subtracting the chemical shifts of the β- d -glucopyranoside from the corresponding chemical shifts of the β- l -glucopyranoside of 5α-cholestan-3β-ol and the triterpene dammarenediol-1. ), and even in the β-D- and α-D-glucopyranosides ( Fig. 10 Download high-res image (152KB) Download full-size image Fig. 10 . The Δδ C p values (in ppm) calculated for the anomeric (C-1′) and aglycon carbons, using the previously reported data of the β- d - and α- d -glucopyranoside pairs of secondary alcohols. ). © 1997 Elsevier Science Ltd.