Studies on the constituents of Syringa species. X. Five new iridoid glycosides from the leaves of Syringa reticulata (Blume) Hara

Five new iridoid glycosides, (8Z)-ligstroside (1), (8Z)-nüzhenide (3), 6'-O-alpha-D-glucopyranosylsyringopicroside (4), 3'-O-beta-D-glucopyranosylsyringopicroside (5) and 4'-O-beta-D-glucopyranosylsyringopicroside (6) were isolated, together with a known one, (8E)-nüzhenide (2), from the leaves of Syringa reticulata. Their structures were established on the basis of chemical and spectral data. Compounds 1 and 3 are the first findings of a (8Z)-oleoside-type secoiridoid. Compound 4 is the first naturally occurring iridoid di-glycoside having an isomaltose.