Chem. Pharm. Bull. 53(6) 674—676 (2005)

distributed in southwestern China, is a traditional Tibetan medicine used as a remedy for hepatitis and cholecystitis. Previous phytochemical investigations using this plant have led to the isolation of various poly-oxygenated xanthones, xanthone glycosides, and flavonoid glucosides. In this paper, we report the isolation and structure elucidation of two new iridoid glycosides senburiside III (2) and senburiside IV (3), from this plant. The n-butanol extract of the whole plant of S. franchetiana on repeated column chromatography and preparative HPLC yielded two new compounds, 2 and 3, in addition to four known compounds, 1, 4—6, as described in the Experimental. Compound 1 was obtained as a white amorphous powder. Its UV (237 nm) and IR (1703, 1634 cm ) absorptions were typical of an iridoidic enol ether system conjugated with a carbonyl group. The NMR spectral data of 1 (shown in Tables 1, 2) agreed with those of senburiside I previously isolated from the Japanese folk herb S. japonica. Senburiside III (2) was obtained as a white amorphous powder. Its UV and IR absorptions were similar to those of senburiside I. The negative atmospheric pressure chemical ionization mass spectrum (APCI-MS) gave a quasimolecular ion at m/z 983 [M H] , corresponding to the molecular formula C47H52O23, supported by elemental analysis (Experimental). In the H-NMR spectrum of 2, the signals at d 7.52 (1H, s) and d 5.68 (1H, br s) assigned to H-3 and H-1 respectively, were typical of an iridoid nucleus; the signals at d 3.09 (1H, m, H-5), 2.62 (1H, m, H-6), 2.18 (3H, m, H-9, H-8, H6), and 1.41 (3H, d, J 6.4 Hz, H-10) were almost identical with those of senburiside I, indicating that 1 and 2 bear similar iridoid nucleus; the proton signals at d 7.76 (1H, d, J 16.0 Hz), d 6.50 (1H, d, J 16.0 Hz), d 7.06 (2H, s) and d 4.05 (6H, s) were attributed to the trans-sinapoyl moiety. The C-NMR data of 2 were quite similar to those of 1, except for the signals arising from an additional glucose moiety and an m-substituted benzoyl group. The correlation between H1 (d 5.23) and C-22 (d 159.5) in the heteronuclear multiple bond correlation (HMBC) spectrum indicated the linkage of the glucose unit to m-hydroxyl of the benzoyl group. It was observed that the signals of C-15 in 2 were shifted upfield to d 152.7 when compared with compound 1, in which it resonated at d 158.9. This indicated that the m-hydroxybenzoyl moiety at the C-7 position was benzoylated in 2. The correlation in HMBC between the carbonyl signal of the sinapoyl moiety at d 168.3 (C-9 ) and the proton signal at d 5.00 which was assigned to H-2 according to its correlations with H-1 (d 5.07) in H–H correlated spectroscopy (COSY) and with C-1 (d 98.3) in HMBC, proved the attachment of the sinapoyl moiety to the C-2 position of the glucose. These linkage positions were also confirmed by fragmental ion peaks in the APCI-MS spectrum of 2 (at m/z 495, 419, 299, 289, 223 and m/z 369 in negative and positive mode, respectively), shown in Fig. 3. The relative stereochemical configuration of 2 was determined by comparison of spectral data with those in the literature. Based on the above mentioned analysis, the structure of senburiside III was determined as shown in 2 (Fig. 1). Senburiside IV (3) was obtained as a white amorphous powder. Its molecular formula C36H42O16 was deduced from its ( )APCI-MS spectrum (the quasimolecular ion peak at 674 Notes Chem. Pharm. Bull. 53(6) 674—676 (2005) Vol. 53, No. 6