Utilization of circular dichroism experiment to distinguish acanthoside D and eleutheroside E.
Two lignan glycosides, acanthoside D (1) (=liriodendrin, (+)-syringaresinol di-O-β-D-glucopyranoside) and eleutheroside E (2) have been confused each other for so long time, and hard to be distinguished each other.  Now, this two compounds need to be defined properly so that all the commercial mistakes and confusions should not be made.  They have identical planar structures except for the configurations at C-7 and C-8 in each structure according to the chemistry database, SciFinder(®).  The systematic name of acanthoside D is [(1S,3aR,4S,6aR)-tetrahydro-1H,3H-furo[3,4-c]furan-1,4-diyl]bis(2,6-dimethoxy-4,1-phenylene) bis-β-D-glucopyranoside (1), and the name of eleutheroside E is [(1R,3aR,4S,6aS)-tetrahydro-1H,3H-furo[3,4-c]furan-1,4-diyl]bis(2,6-dimethoxy-4,1-phenylene) bis-β-D-glucopyranoside (2).  The differences at two chiral centers do not make any differences in the NMR spectra.  Thus, the circular dichroism were utilized to dissolve this difficult problem.  Acanthoside D (1) showed a positive Cotton effect at 200 nm, whereas eleutheroside E (2) exhibited a negative cotton effect at 200 nm.  The absolute structure of acanthoside D was also confirmed by X-ray crystallography.