Alisma orientalis (SAM.) JUZEP. is widely cultivated in China and Japan, and the dried rhizomes are a crude drug for the treatment of diabetes and diuretics. 1) Our previous paper 2) reported that a serious protostane-type triterpenes extracted from this plant showed anti-hepatitis B virus (HBV) activity. As a subsequent study on this plant, further investigation on the less polar part of the 90% EtOH extract of the dried rhizomes of A. orientalis led to the isolation of two new sesquiterpenes: alismorientols A (1) and B (2) (Fig. 1 (Table 1). NMR spectral analysis revealed that compound 1 was a guaiane-type sesquiterpenoid.
13C DEPT experiment showed that compound 1 possessed the same numbers of methyls, methylenes, methines, and quaternary carbons as those of orientaol E.3) However, the chemical shifts for the C-atoms of 1 were not identical with those of orientaol E, 3) especially for C-4 (d 83.3), C-5 (52.0), C-7 (d 76.5), C-9 (37.6), C-10 (d 71.7), and C-14 (d 32.8). The chemical shifts for other C-atoms in 1 were also shifted downfield about 1 to 2 ppm. Considering the different solvent, the down-shift chemical shifts of those carbons could be explained.The differences between compound 1 and orientaol E are focused on C-4, 5, 7, 9, 10, and C-14. ESI-MS established that compound 1 had mass 18 units more than orientalol E, accounting for one molecule of H 2 O was added to the epoxyl of C-10 and C-7 of orientalol E to form compound 1, deducing one additional OH group presented in compound 1, which could be supported by the HMBC experiment. In the HMBC spectrum (Fig. 2), no correlation between H-14 and C-7 could be found, demonstrating no epoxy attached between C-7 and C-10. The other long-range correlations between protons and carbons in HMBC were also given as follows: H-14 and H-5 with C-1, H-5, H-3, and H-15 with C-4, H-5 with C-6, H-6, H-11, H-12, H-13 with C-7, C-11, H-6 with C-11, H-12, and H-13 with C-11. The relative stereostructure of 1 characterized by ROESY experiment accounted for the very different chemical shifts of C-4, 5, 9, and C-14. As shown in Fig. 2, correlations between H-1, assumed to be a-oriented, and H-5, Me-14 were observed, besides correlation between H-5 and H-6, suggesting that H-5, 6, and Me-14 were in a-orientation. The a-configuration for H-6 could also be concluded by the coupling constant of H-6 at d 4.51 (br s). Consequently, compound 1 was established as 4a,6b,7a,10b-tetrahydroxy-1,5-cis-guaiane (1), which was also confirmed by X-ray crystallographic analysis (Fig. 3).Compound 2 was obtained as a colorless prism. The IR spectrum of 2 exhibited absorptions for OH groups at 3406 cm Ϫ1 and an olefinic moiety at 1634 cm Ϫ1 . The molecular formula was deduced to be (Table 1), four tertiary methyl signals were observed, together with an olefinic proton at d H 5.87 (1H, d, Jϭ2.9 Hz, H-6). The 13 C-NMR spectrum of 2 revealed the presence of 15 carbon signals, of which two olefinic carbons [d C 121.6 (C-6, d), 150.0 (C-7, s)] were observed. The above spectral features suggested 2 ...