Chem. Pharm. Bull. 54(7) 992—995 (2006)

genus and is predominately distributed in the tropical region of Asia, the Pacific Islands, and Australia. Taccalonolides, anthocyanins, diarylheptanoids and diarylheptanoid glucosides, steroidal sapogenins and steroidal glycosides such as C-27 steroidal saponins, C-28 sterol glucosides and withanolide glucosides have been isolated from some Tacca species. Tacca plantaginea (HANCE) is a perennial plant that grows in southeastern China. Its rhizomes is a folk medicine used as analgesic, antipyretic, anti-inflammatory agents and for the treatment of incised wounds. Chen and co-workers have reported the isolation and purification of the highly oxygenated taccalonolides from the rhizomes of T. plantaginea. Taccalonolides A and E were claimed to be important for initiation of paclitaxel-like microtubule bundling; therefore, they represent the first plantderived microtubulestabilising agents to be identified since paclitaxel and the first natural steroids to show microtuble-stabilizing activity. Previously, we have reported two new steroidal saponins from this whole plant. Further chemical investigation on the CHCl3 soluble part of the EtOH extracts of this plant resulted in the isolation of five new withanolides, named plantagiolides A—E (1, 3—6). The known chantriolide A (2) was separated from the AcOEt soluble part. The structures of the five new compounds were determined by analysis of their spectral data, especially two dimensional (2D) NMR spectra. Herein, we reported the isolation and structural elucidation of those compounds. Plantagiolide A (1) was obtained as colorless needles. Its molecular formula of C32H42O11 was established by the positive high-resolution electrospray ionization mass spectrum (HR-ESI-MS) ([M Na] , m/z 625.2623) and C-NMR spectrum (Table 2), a molecular formula corresponding to 12 degrees of unsaturation. A careful comparison the Hand C-NMR data of 1 with those of the aglycone of chantriolide A (2), it was obvious that compound 1 was the aglycone of chantriolide A (2) and the stereochemistry of compound 1 was same as that of the aglycone of chantriolide A (2). Accordingly, the structure of 1 was elucidated as (20S,22R)1a ,12a -diacetoxy-2a ,3a ;6a ,7a -diepoxy-5a ,27-dihydroxy16-oxowith-24-enolide, named plantagiolide A, which was firstly obtained as natural compound. Plantagiolide B (3), a white amorphous powder, showed a molecular ion peak at m/z 605 [M H] in its positive fast atom bombardment mass spectrometry (FAB-MS), consistent with a molecular formula C32H44O11 (11 degrees of unsaturations), as confirmed by its (HR)-ESI-MS ([M Na] , m/z 627.2776) and C-NMR spectrum. By step-by-step comparison of the Hand C-NMR spectral features of 3 with those of 1, the other signals of 3 were similar to those of 1 except for the disappearance of a carbonyl group and the presence of a hydroxyl group located at C-16 (d 70.6) and an oxygenated methine (d 4.34) in compound 3. Therefore, it was supposed that the carbonyl group at C-16 was protonated to hydroxyl group in compound 3, which was confirmed by the mass difference of m/z 2 and the heteronuclear multiple bond correlation (HMBC) spectrum. In the HMBC spectrum of 2, the correlations of H-14 (d 2.54, dd, J 8.0, 10.0 Hz), Ha-15 (d 2.50, m), Hb-15 (d 1.40, m), H-17 (d 1.64, m), and H-20 (d 2.36, m) with C-16 (d 70.6, d) were observed. The relative configuration of the hydroxyl group in C-16 was determined by ROESY experiment (Fig. 1). The H-16 signal showed ROESY correlations with H-14 and H-17 suggesting a a-orientation of H-16. On the basis of above evidence, the structure of 3 was established as (20S,22R)-1a ,12a-diacetoxy-2a ,3a ;6a ,7a -diepoxy-5a ,16b ,27-trihydroxywith-24enolide, named plantagiolide B, which was the aglycone of chantriolide B. Plantagiolide C (4) was isolated as colorless needles. The (HR)-ESI-MS of 3 displayed a [M Na] peak at m/z 611.2835, corresponding to the empirical molecular formula of C32H44O10, which was also deduced by analysis of its CNMR and DEPT spectral data. The mass spectrum indicated that compound 4 was 14 mass units less than compound 1. The Hand C-NMR spectral data of 4 were close to those of 1. The only significant differences included the absence 992 Vol. 54, No. 7