950
J. Nat. Prod. 2001, 64, 950-952
Taxane Diterpenoids from the Stem Bark of Taxus mairei Ya-Ching Shen,*,† Chaturvedula V. S. Prakash,† Yin-Ju Chen,‡ Jeng-Fen Hwang,‡ Yao-Haur Kuo,§ and Ching-Yeu Chen† Institute of Marine Resources, National Sun Yat-sen University, 70 Lien-Hai Road, Kaohsiung, Taiwan, Republic of China, Department of Pharmacy, Chia-Nan University of Pharmacy and Science, Tainan, Taiwan, Republic of China, and National Research Institute of Chinese Medicine, Taipei, Taiwan, Republic of China Received February 13, 2001
Three new 11(15f1)-abeo-taxanes, taxumairols U-W (1-3), have been isolated from extracts of the stem bark of Formosan Taxus mairei. The structures of 1-3 were identified as 5R,7β,9R,13R,20-pentaacetoxy2R,10β,15-trihydroxy-11(15f1)-abeo-taxene, 5R,7β,9R,20-tetraacetoxy-2R,10β,13R,15-tetrahydroxy-11(15f1)-abeo-taxene, and 2R,4R,7β,10β-tetraacetoxy-5β,20-epoxy-9R,13R,15-trihydroxy-11(15f1)-abeotaxene, respectively, on the basis of 2D NMR techniques including COSY, HSQC, HMBC, and NOESY experiments as well as chemical reactions of compounds 1-3 to give 4 (5R,7β,9R,10β,13R,20-hexaacetoxy2R,15-dihydroxy-11(15f1)-abeo-taxene) and 5 (4R,7β,10β-triacetoxy-9R,13R-dibenzoxy-5β,20-epoxy2R,15-dihydroxy-11(15f1)-abeo-taxene), which are also novel taxane derivatives. Taxumairols U (1) and V (2) exhibited significant cytotoxicities against human hepatoma tumor cells, while taxumairol W (3) was inactive. More than 100 taxoids have been isolated from the Taiwanese yew Taxus mairei (Lemee & Levl.) S. Y. Hu. Previous studies on diterpenoids of T. mairei have resulted in the isolation of 13-deacetylcanadensene and 7-deacetylcanadensene and novel taxachitrienes from the leaves,1 taxumairols N and O from the roots,2 and taxumairol R from the root bark.3 Two new abeo-taxanes, taxumains A and B, both with an opened oxetane ring, were isolated from the twigs of this plant.4 Recently, taxumairol M and taxumairone A were isolated from its seeds.5,6 As part of searching for practical and renewable sources of Taxol and useful taxoids for SAR study,7,8 we now report the isolation and structure elucidation of three novel taxoids (1-3) from the stem bark of T. mairei. The EtOH extract of the stem bark of the Taiwanese yew T. mairei yielded compounds 1-3. Taxumairol U (1) had a molecular formula of C30H44O13 as deduced from highresolution FABMS. Its IR bands indicated the presence of hydroxyl (3462 cm-1) and acetyl (1734 cm-1) groups. The 1H NMR data of 1 showed five acetyl singlets (δ 2.04, 2.05, 2.06, 2.10, 2.13), four typical methyl singlets (δ 0.97, 1.12, 1.41, 1.85), a double doublet at δ 2.53 (H-3, J ) 7.5, 4.5 Hz), a doublet at δ 5.05 (H-5, J ) 2.5 Hz), and two pairs of coupled systems at δ 3.92, 4.37 (H-20), 4.63, and 5.57 (H10, 9). Detailed analysis of the 1H and 13C NMR, COSY, and HSQC spectra revealed that 1 is a 5/7/6 taxene with an opened oxetane ring.9 This 11(1f15)-abeo-taxane skeleton bearing a dimethyl carbinol group in C-1 was confirmed from the observation of adjacent quaternary sp3 carbons at δ 69.0 (C-1) and 76.3 (C-15) and cross-peaks from Me-16 (δ 1.41) and Me-17 (δ 1.12) to C-1 and C-15 as well as correlations of geminal dimethyl (16/17) in the HMBC spectrum. The remaining two hydroxyl groups were determined at C-2 and C-10 by observation of HMBC correlation of H-2 (δ 4.64) to C-3 (δ 41.0), C-8 (δ 43.2), and C-15 (δ 76.3) and H-10 (δ 4.63) to C-9 (δ 79.8) and C-11 (δ 140.7). A comparison with literature data indicated that taxumairol U (1) is an isomer of taxayuntin J (6), isolated from T. yunnanensis. Upon acetylation, compound 1 yielded a novel compound 4, which showed only an additional ace* To whom correspondence should be addressed. Tel: (886) 7-525-2000, ext. 5058. Fax: (886) 7-525-5020. E-mail:
[email protected]. † National Sun Yat-sen University. ‡ Chia-Nan University of Pharmacy and Science. § National Research Institute of Chinese Medicine.
10.1021/np010071r CCC: $20.00
tyl singlet at δ 1.94 in the 1H NMR spectrum, while the C-2 hydroxyl group could not be acetylated. Also, the overlapping H-10 was shifted from 4.63 ppm in 1 to 6.24 ppm in 2. Detailed assignments of protons and corresponding carbons were completed by COSY and HSQC experiments. The NOESY correlations of H-2/H-9, Me-16, Me-19, and H-9/Me-19 in 1 suggested that H-2, H-9, Me-19, and the dimethyl carbinol group were in β-orientation. Correlations between H-3/H-7 and H-10/Me-18 agreed with the R-configuration of H-3, H-7, and H-10. A coupling constant between H-9 and H-10 of 9.0 Hz indicated a transrelationship.
© 2001 American Chemical Society and American Society of Pharmacognosy Published on Web 06/16/2001
Notes
Journal of Natural Products, 2001, Vol. 64, No. 7 951
Table 1. Cytotoxicity of Taxoids 1-5 against Human Tumor Cells (IC50, µg/mL)a taxumairol U (1) taxumairol V (2) taxumairol W (3) 4 5 paclitaxel
KB
Hepa
10.3 3.9 >20 >20 >20 20
