Secoiridoid gylcosides from Swertia mileensis

From the MeOH extract of the aerial parts of Swertia mileensis, four new secoiridoid glycosides were isolated, 4'-O-[(E)-caffeoyl]swertiamarin (1), 4'-O-[(Z)-coumaroyl]swertiamarin (7), 6'-O-[(E)-coumaroyl]swertiamarin (8), and 6'-O-[(Z)-coumaroyl]swertiamarin (9), together with five known compounds. Their structures were elucidated by NMR spectroscopy and tandem mass spectrometry. Detailed HPLC/MS analyses and MS/MS fragmentation pathways are discussed for the identification of the swertiamarin-derived (E)I(Z) isomers 6/7 and 8/9.