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)/(Z) isomers 6/7 and 8/9.
Introduction. -Swertia mileensis T. N. HE et SHI, traditionally known as 'Qing-Ye-Dan', is a species of Swertia, belonging to the family Gentianaceae. This plant has long been used as a folk medicine in Yunnan Province, China, to treat virus-induced hepatitis [1 -3]. Previous phytochemical investigations of this plant revealed the presence of secoiridoid glucosides and acyl secoridoid glucosides [3 -5], of which swertiamarin and sweroside, which display antihepatotoxic and antitumor activities, are the main components [6]. Other compounds identified in this plant include xanthones, triterpenoids, and monoterpenoid glycosides [7 -9].
The continuous investigation and careful examination of S. mileensis led to the isolation of nine compounds, 1 -9, including four new secoiridoid glycosides, 1 and 7 -9, and of five known compounds, 2 -6. This paper deals with the isolation and structure elucidation of the new compounds, and the application of HPLC-UV-MS methods for the discrimination of swertiamarins with (E)-vs. (Z)-configured coumaroyl substituents on their glycones (compounds 6 -9).
Results and Discussion. -The MeOH extract from the aerial parts of S. mileensis was investigated by liquid chromatography with photodiode-array and electrosprayionization-mass-spectrometric detection (HPLC/PDA/ESI-MS). A total of nine wellseparated signals were observed, and the corresponding compounds isolated (Table 1). Comparison of the HPLC profiles of the pure secoiridoid glycosides with the original crude MeOH extract showed that all compounds are naturally occurring.
Compound 1 was obtained as a colorless, amorphous powder. Its molecular formula was determined as C 25 H 28 O 13 by HR-FAB-MS (m/z 535.1528 ([M Γ H] Γ ; calc. 535.1452)). Its IR spectrum indicated the presence of OH groups (3107, 3474 cm Γ1 ) and of a conjugated C=O group (1697, 1613 cm Γ1 ). The structure of 1 was established by analysis of 1 H-and 13 C-NMR (see Tables 2 and3 in the Exper. Part, resp.), DEPT, HSQC, HMBC, and tandem-MS experiments.