Chem. Pharm. Bull. 54(1) 126—128 (2006)

found in Southeast China and Southeast Asia. The fruits are edible and abundant in ( )-hydroxycitric acid, and the latex and the bark have some prenylated xanthones which show mainly a 1, 3, 6, 7 oxygenation pattern. The constituents of the young stems of the species from Southeast China were investigated for bioactive xanthones. This paper reports the isolation and characterization of two new xanthones, 1,5,6trihydroxy-3-methoxy-4-(3-hydroxyl-3-methylbutyl)xanthone (1) and 1,5-dihydroxy-3-methoxy-6 ,6 -dimethyl-2Hpyrano(2 ,3 :6,7)-4-(3-methylbut-2-enyl)xanthone (2), along with six known xanthones: 1,3,5-trihydroxy-6 ,6 -dimethyl2H-pyrano(2 ,3 :6,7)xanthone (3), dulxanthone A (4), 1,5,6-trihydroxy-3,7-dimethoxyxanthone (5), 1,7-dihydroxyxanthone (6), 1,3,5-trihydroxy-6-methoxyxanthone (7), 1,3,6,7-tetrahydroxyxanthone (8), from the stems of this plant. Compounds 1—4, 7 have a 1, 3, 5, 6 oxygenation pattern of the xanthone nucleus. Examination of their bioactivities is now in progress. Compound 1, obtained as a pale yellow amorphous powder, had the molecular formula C19H20O7 based on m/z 360.1216 (M ) by high-resolution electron impact mass spectroscopy (HR-EI-MS). Its UV (234, 252, 285, 326 nm) and IR (3469, 1641 cm ) showed absorptions characteristic of 1,3,5,6-tetraoxygenated xanthone. In the H-NMR spectrum, four hydroxyl signals [dH 4.32, 9.06, 10.51 (1H, each, br s), and 13.11 (1H, s, chelated)] were observed; two one-proton doublets [dH 6.87, 7.46, each J 9 Hz] were further exhibited in addition to a methoxyl singlet [dH 3.85 (3H, s)]. The spectrum also showed the presence of two methyl groups in a singlet [dH 1.12 (6H, s)] and two methylene groups as two triplets [dH 1.52, 2.77, each J 8.5 Hz], implying the presence of a 3-hydroxyl-3-methylbutyl side chain. The C-NMR data of 1 (see Table 1) had a strong resemblance to 4 (characterized as dulxanthone A) indicating a xanthone skeleton with a similar substitution pattern. Furthermore, the Hand C-NMR spectroscopic assignments for 1 were determined by the HSQC and HMBC spectrum (see Fig. 2). In the HMBC spectrum, cross-peaks the chelated hydroxyl proton dH 13.11 (1-OH)/dC 94.1 (C-2) and 101.9 (C-9a), dH 6.42 [H-2]/dC 160.9 (C-1), 101.9 (C-9a) and 163.4 (C-3), dH 3.85 (3-OCH3)/dC 163.4 (C-3) were observed; correlations dH 2.77 [H-1 ]/dC 163.4 (C-3), 153.5 (C4a) and 108.5 (C-4), dH 1.52 [H-2 ]/dC 108.5 (C-4) were present, which confirmed the A-ring feature of 1. Furthermore, one hydroxyl group dH 9.06 [5-OH] showed correlations to dC 152.2 (C-6), 132.5 (C-5) and 146.5 (C-10a), another hydroxyl group dH 10.51 [6-OH] was correlated to dC 152.2 (C-6), 132.5 (C-5) and 112.9 (C-7); correlation between dH 7.46 [H-8] and dC 180.8 (C-9) was observed, which indicated the position of two hydroxyl groups in the B-ring. Thus, compound 1 was determined to be 1,5,6-trihydroxy-3methoxy-4-(3-hydroxyl-3-methylbutyl)xanthone. Compound 2 was isolated as yellow needles, mp 217— 218 °C, C24H24O6 (m/z 408.1552), had UV and IR spectral data suggestive of a xanthone derivative. What is more, 2 showed analogous UV features to nigrolineaxanthone B (1,5dihydroxy-3-methoxy-6 ,6 -dimethyl-2H-pyrano(2 ,3 :6,7)4-(3-hydroxyl-3-methylbutyl)xanthone) also suggesting the presence of a 1,3,5,6-tetraoxygenated xanthone chromophore. In the H-NMR spectrum, two hydroxyl groups [dH 9.37 (1H, br s), and 13.14 (1H, s, chelated)] were observed; in addition to a methoxyl singlet [dH 3.90], a set of signals due to a prenyl group [dH 3.46 (2H, d, J 7.5 Hz), 5.20 (1H, t, J 7.5 Hz), 1.79 (3H, s), 1.61 (3H, s)] was present; there were two aromatic proton signals at dH 7.38 and 6.49 (each 1H, s), the signal in lower field [dH 7.38] was assigned to H-8 which was strongly deshielded by the carbonyl, and the other signal at dH 6.49 (1H, s) was indicative of H-2 or H-4. Two one-proton doublets [dH 6.57, 5.88, each J 10 Hz] along with two methyl groups [dH 1.45, 6H, s] suggested the presence of a 2,2-dimethylpyran ring. Thus, the structure of 2 was characterized by the HSQC and HMBC spectrum (see Fig. 2). In the HMBC spectrum (as shown), cross peaks dH 13.14 (1-OH)/dC 94.3 (C-2) and 102.0 (C-9a), dH 3.90 (3-OCH3)/dC 163.6 (C-3) were observed; dH 3.46 [H-1 ] was correlated to dC 163.6 (C-3), 153.1 (C-4a) and 107.5 (C-4), which confirmed a prenyl group was attached to C-4. Furthermore, the A-ring feature of 2 was confirmed by comparison of the C-NMR data with the isolated compounds 1 and 4 (see Table 1) including literature values. The presence of a dimethylpyran ring fused with the B ring of the 1,3,5,6-tetraoxygenated xanthone nucleus at C-6 and C-7 was determined by three C–H threebond correlations dH 5.88 [H-5 ]/dC 118.2 (C-7), dH 6.57 [H4 ]/dC 146.3 (C-6) and 112.1 (C-8). Since there was no other proton signal the substituent at C-5 must be a hydroxyl group, which was established by HMBC correlations dH 9.37 [5-OH]/dC 133.2 (C-5), 146.3 (C-6) and 146.3 (C-10a). Accordingly, compound 2 was elucidated as 1,5-dihydroxy-3methoxy-6 ,6 -dimethyl-2H-pyrano(2 ,3 :6,7)-4-(3-methylbut-2-enyl)xanthone.