Cytotoxic cycloartane triterpenoids from Gardenia spp.

Abstract

In a phytochemical investigation of bioactive compounds from Gardenia spp., G. sootepensis, G. tubifera, G. obtusifolia, G. thailandica and G. collinsae were selected for isolation, purification and structure elucidation of their chemical constituents. The chromatographic separation of apical buds of G. sootepensis led to the isolation of seven new 3,4-seco-cycloartane triterpenes, sootepins A-G, along with five known compounds, coronalolide, cornalolide methyl ester, tubiferolide methyl ester, secaubryenol, and coronalolic acid. The same treatment with G. tubifera yielded three novel furano-3,4-seco-cycloartane triterpenes, gardenoins A-C, and a normal 3,4-seco-cycloartane triterpene, gardenoin D. Additionally, the apical buds of G. obtusifolia provided four new cycloartane triterpenes, gardenoins E-H, along with four know compounds, dikamakiartanes A, C, D, and 5α-cycloart-24-ene-3,16,23-trione. The exudate of G. thailandica provided two additional new 3,4-seco-cycloartane triterpenoids, gardenoin I and J. Unlike other species, the isolation of G. collinsae buds yielded a new dammarane triterpenes and its C-24 epimer. Their structures were elucidated on the basis of spectroscopic methods (1D and 2D NMR, HREIMS, and X-ray diffraction analysis). All isolated compounds were tested for in vitro cytotoxic activity against human breast (BT474), lung (CHAGO), liver (Hep-G2), gartric (KATO-3), and colon (SW-620) cancer cell lines. Generally, the compounds possessing an exomethylene γ-lactone moiety showed broad cytotoxicity for all cell lines tested in 5-10 micromolar range, while the compounds without an α-methylene-γ-butyrolactone ring showed no significant activities. The structure activity relationship of isolated compounds, sootepin A and coronalolide. The ester derivatives of sootepin A at C-26 did not improve the cytotoxicity effect, while the amide and ester derivatives of coronalolide at C-3 are also result. Moreover, the reaction of α-methylene-γ-butyrolactone and some nucleophiles displayed these group was necessary for the cytotoxicity. Finally, the sootepin G showed the significant apoptotic with Hep-G2 cancer cell line.