Elsevier

Tetrahedron

Volume 58, Issue 40, 30 September 2002, Pages 8073-8086
Tetrahedron

Cytotoxic and anti-HIV-1 constituents of Gardenia obtusifolia and their modified compounds

https://doi.org/10.1016/S0040-4020(02)00999-7Get rights and content

Abstract

5α-Cycloart-24-ene-3,23-dione (1), 5α-cycloart-24-ene-3,16,23-trione (2) and methyl 3,4-seco-cycloart-4(28),24-diene-29-hydroxy-23-oxo-3-oate (3), together with five known flavones 5,7,4′-trihydroxy-3,8-dimethoxyflavone (4), 5,7,4′-trihydroxy-3,8,3′-tri-methoxyflavone (5), 5,7,4′-trihydroxy-3,6,8-trimethoxyflavone (6), 5,4′-dihydroxy-3,6,7,8-tetramethoxyflavone (7) and 5,3′-dihydroxy-3,6,7,8,4′-pentamethoxyflavone (8) have been isolated from the leaves and twigs of Gardenia obtusifolia. The structures were assigned on the basis of spectroscopic methods. Compounds 38 and some of the modified compounds showed significant cytotoxic activities in several mammalian cell lines, especially 8 and its diacetate 21 which exhibited potent cytotoxicities (compound 8: P-388 0.05 μg/mL, KB 0.09 μg/mL, BCA-1 0.63 μg/mL, Lu-1 0.09 μg/mL, ASK 0.70 μg/mL; its diacetate: P-388 0.27 μg/mL, KB 0.06 μg/mL, BCA-1 0.53 μg/mL, Lu-1 0.49 μg/mL). It was also found that 5, 8 and 21 showed antimitotic acitivity in the ASK assay. Compounds 2, 4, 6, 7 and some of the modified compounds displayed interesting anti-HIV activity in the syncytium assay, but were inactive or exhibited weak activity in the HIV-1 RT assay; while compound 3 was found to be active in the HIV-1 RT assay (99.9 % inhibition at 200 μg/mL), but cytotoxic in the syncytium assay.

Natural compounds 13 and five 3-methoxyflavones were isolated from Gardenia obtusifolia. All isolated constituents, together with the modified compounds, were evaluated for cyclotoxic and anti-HIV activities.

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Introduction

More than 80 species in the genus Gardenia (Rubiaceae) are widely distributed among the tropical forests in various parts of the world. Fifteen species of Gardenia were reported in Thailand.1 Several species of Gardenia have been recorded to be used ethnomedically in various countries primarily for abortifacient2 and contraceptive2., 3., 4. purposes. Some species are used as a febrifuge,5 for the treatment of headaches6 and as a larvicides.7 Extracts of various Gardenia species showing anti-implantation and abortifacient effects,8 as well as antiulcer,9 antibacterial,10 analgesic,11 diuretic,11 hypertensive11 and larvicidal activity12 have been previously reported. As part of our ongoing project on the discovery of new anti-cancer and anti-HIV agents from plants, several species of Gardenia have been collected from various parts of Thailand. Our previous work on Gardenia coronaria and G. sootepensis13 has resulted in the isolation of four ring-A seco-cycloartane triterpenes. In this work, the chloroform fraction of Gardenia obtusifolia Roxb. was studied and led to the isolation of 5α-cycloart-24-ene-3,23-dione (1), 5α-cycloart-24-ene-3,16,23-trione (2), methyl 3,4-seco-cycloart-4(28),24-diene-29-hydroxy-23-oxo-3-oate (3); along with five known flavones 5,7,4′-trihydroxy-3,8-dimethoxyflavone (4), 5,7,4′-trihydroxy-3,8,3′-trimethoxyflavone (5), 5,7,4′-trihydroxy-3,6,8-trimethoxyflavone (6), 5,4′-dihydroxy-3,6,7,8-tetramethoxyflavone (7) and 5,3′-dihydroxy-3,6,7,8,4′-pentamethoxyflavone (8) (Fig. 1). Compound 1 has been isolated previously from the stem bark of Monocyclanthus vignei,14 the bud exudates of Fijian Gardenia species15 and the leaves of Guarea trichilioides,16 while 2 and 3 are new compounds. For further structure–activity studies, the new cycloartane derivatives 915 and the known flavone derivatives 1622 (Fig. 1) were prepared from the isolated compounds. The structures of all compounds were elucidated on the basis of spectroscopic methods. We herein describe the isolation, the modification and the determination of the structures, including their cytotoxic and anti-HIV activities. There have been no reports either on phytochemistry or biological activity of G. obtusifolia prior to our work.

Section snippets

Results and discussion

Compound 1 exhibited [M]+ peak at m/z 438 in the EIMS corresponding to a molecular formula C30H46O2. Its IR (CHCl3) spectrum showed the absorption bands at νmax 1698 cm−1 (for 6-membered ring ketone), 1683 cm−1 (for conjugated ketone), and 1616 cm−1 (for CC). The 1H NMR spectrum (Table 1) of 1 displayed a characteristic pair of doublets for cyclopropane methylene protons17., 18., 19., 20., 21., 22., 23., 24. at δ 0.58 and 0.79 (1H each, d, J=4.3 Hz), as well as the three singlet signals for the

Bioassay evaluations

Pure compounds 122 were evaluated for cytotoxic effects against a panel of cultured mammalian cell lines.34 The results including their antimitotic activities are as shown in Table 7. Moderate to high potency of cytotoxicities were found in compounds 38, 12, 20 and 21, while compounds 5, 8 and 21 exhibited antimitotic effects in the ASK assay. It should be noted that compound 8 and its diacetate 21 showed high potent cytotoxicity comparable to other compounds in Table 7.

All of the isolated

Conclusion

In conclusion, it is interesting to note that although the occurrence of cycloartane triterpenes and highly oxygenated flavonol methyl ethers have been reported in several species of plants, compounds possessing significant cytotoxic and anti-HIV activities are particularly rare. To the best of our knowledge, the structure modification of the isolated cycloartanes to obtain better biological activities has not been attempted. Our work represents an example of an investigation of both chemical

General procedures

Mps: uncorr.; UV: EtOH or MeOH; IR: CHCl3 or KBr. NMR spectra were recorded on a Bruker DPX 300 in CDCl3 using TMS as an internal standard, otherwise stated; CC was carried out on silica 60, 70–230 mesh.

Plant material

The leaves and twigs of G. obtusifolia Roxb. (Rubiaceae) were collected from Chiang Mai Province of Thailand in March, 1996, and identified by one of us (T. S.). A voucher specimen (BKF no. 092419) of G. obtusifolia has been deposited at the Forest Herbarium, Royal Forest Department, Bangkok,

Acknowledgements

We wish to acknowledge the financial support from the National Research Council of Thailand (NRCT). We also thank the Higher Education Development Project: Postgraduate Education and Research Program in Chemistry and the Thailand Research Fund (TRF) through a Senior Scholar Award to V. R. for the partial support. W. P. is grateful to the Institutional Strengthening Program, Faculty of Science, Mahidol University, for providing a research scholarship.

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