Studies on the constituents of Swertia japonica MAKINO I. On the structures of new secoiridoid diglycosides

Eight new secoiridoid diglycosides, 6′-O-α-L- arabinopyranosylswertiamarin (1), 3′-O-β-D-glucopyranosylswertiamarin (2), 4′-O-β-D-glucopyranosylswertiamarin (3), 3′-O-β-D- galactopyranosylswertiamarin (4), 6′-O-α-D- galactopyranosylswertiamarin (5), 6′-O-α-D- mannopyranosylswertiamarin (6), 6′-O-β-D-fructofuranosylswertiamarin (7) and 5″-O-β-D-glucopyranosylamaroswerin (12), were isolated, together with five known compounds from the whole plants of Swertia japonica MAKINO. The structures of the new compounds were elucidated on the basis of chemical and spectroscopic evidence. Compounds 6 and 7 are the first naturally occuring iridoid diglycosides having an α-D-mannopyranosyl unit and β-D-fructofuranosyl unit, respectively.