In vitro cytotoxic potential of extracts from Aristolochia foetida Kunth against MCF-7 and bMECs cell lines.

The aim of this study was to evaluate the cytotoxic potential of Aristolochia foetida Kunth. Stems and leaves of A. foetida Kunth (Aristolochiaceae) have never been investigated pharmacologically. Recent studies of species of the Aristolochiaceae family found significant cytotoxic activities. Hexane, dichloromethane, ethyl acetate and methanol extracts were analyzed by 1H NMR and GC-MS to know the metabolites in each extract. In GC-MS analysis, the main compounds were methyl hexadecanoate (3); hexadecanoic acid (4); 2-butoxyethyl dodecanoate (9); ethyl hexadecanoate (20); methyl octadeca-9,12,15-trienoate (28) and (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid (40). The results showed a significant reduction in cell viability of the MCF-7 (breast cancer) cell line caused by organic extracts in a dose-dependent manner. The cytotoxicity activity of the dichloromethane extract from the stems (DSE) showed IC50 values of 45.9 µg/mL and the dichloromethane extract of the leaves (DLE) showed IC50 values of 47.3 µg/mL. DSE and DLE had the highest cytotoxic potential in an in vitro study against the MCF-7 cell line and non-tumor cells obtained from the bovine mammary epithelial (bMECs). DSE and DLE induced a loss in mitochondrial membrane potential (ΔΨm) and can cause cell death by apoptosis through the intrinsic pathway in the MCF-7 cell line. DSE and DLE are cytotoxic in cancer cells and cause late apoptosis. Higher concentrations of DSE and DLE are required to induce a cytotoxic effect in healthy mammary epithelial cells. This is the first report of the dichloromethane extract of A. foetida Kunth that induces late apoptosis in MCF-7 cancer cells and may be a candidate for pharmacological study against breast cancer.

Novel Sesquiterpenoid Skeletons by Wagner-Meerwein Rearrangements of Longipinane-9,13-diol-1-one Derivatives.

The partial or total hydrolysis of (3R,4S,5S,6S,9R,10R,11R)-9,13-diangeloyloxylongipinan-1-one (1), isolated from the roots of Stevia viscida, gave alcohols 2 or 3, respectively, which were subjected to molecular rearrangements with boron trifluoride etherate. Compound 2 afforded (3R,4R,5R,6S,9R,10S,11S)-11,13-oxyneomorelian-1-one (10) and (4S,5R,6S,8S,10R)-10,13-oxyneojiquilp-2-en-1-one (11), both possessing novel sesquiterpenoid skeletons. In turn, 3 provided (3R,4R,5S,6S,9R,11R)-13-hydroxymoreli-10(14)-en-1-one (7) and 10. Acetylation of 3 gave 4, thus allowing reduction of the C-1 carbonyl group to yield 5, which was rearranged to (1S,3R,4S,5S,6S,9R,10R,11R)-13-acetoxy-9,11-epoxyjiquilpane (6), while an attempt to mesylate 3 directly gave rearranged (3R,4R,5S,6S,9R,11R)-13-mesyloxymoreli-10(14)-en-1-one (8) through expulsion of the C-9 mesylate group by the antiperiplanar C-4-C-10 bond migration to C-4-C-9. In addition, treatment of 1 with boron trifluoride etherate generated (3R,4R,5S,6S,9R,11R)-13-angeloyloxymoreli-10(14)-en-1-one (9). The structures of 2-11 were elucidated by 1D and 2D NMR experiments and those of 2, 3, 8, 10, and 11 were confirmed by single-crystal X-ray diffraction analysis.

Novel Sesquiterpene Skeletons by Multiple Wagner-Meerwein Rearrangements of a Longipinane-1,9-diol Derivative.

The tricyclic sesquiterpene (1R,3R,4S,5S,7S,8S,9S,10R,11R)-7,8-diangeloyloxylongipinan-1,9-diol, or rasteviol (7), underwent multiple Wagner-Meerwein molecular rearrangements and several hydride shifts when treated with Et2O-BF3 to generate the six new compounds (1R,3R,4S,5R,7S,8S,9S,10R,11S)-7,8-diangeloyloxy-1,9-epoxyjiquilpane (8), (1R,3R,4S,5R,7R,8S,9S,11S)-8-angeloyloxy-1,7-epoxyzamor-10(14)-ene (11), (2S,3R,4R,5R,6R,7R,8S,9S,10S)-7,8-diangeloyloxy-6,9-epoxyjanitziane (14), (4R,5R,7S,8S,9S,10S,11S)-7,8-diangeloyloxy-9-hydroxyjiquilp-3(15)-ene (16), (2S,3S,5R,7S,8R,10S,11R)-7,8-diangeloyloxyiratzian-9-one (18), and (2S,3S,5R,10S,11R)-8-angeloyloxyiratzi-7-en-9-one (22), of which 8, 11, 14, and 18 possess new hydrocarbon skeletons. Their structures were determined by 1D and 2D NMR in combination with single-crystal X-ray diffraction analyses of derivatives 10, 15, 20, and 21, which allowed confirmation of their absolute configurations by means of the Flack and Hooft parameters. In addition, some reaction mechanism information was gained from deuterium labeling experiments.

Absolute configuration of phomactatriene diterpenoids obtained by Wagner-Meerwein rearrangement of epimeric verticillols.

The epimeric diterpenes (+)-(1S,3E,7E,11S,12S)-verticilla-3,7-dien-12-ol (1), isolated from Bursera suntui, and (+)-(1S,3E,7E,11S,12R)-verticilla-3,7-dien-12-ol (2), isolated from Bursera kerberi, gave the same Wagner-Meerwein rearrangement product (-)-(1E,4Z,8Z,11S,12R)-phomacta-1,(15)4,8-triene (3). The Et2 O:BF3 -induced transformations evidence that verticillenes and phomactanes, both containing the bicyclo[9.3.1]pentadecane skeleton, are biogenetically related through the verticillen-12-yl cation (A+ ), which also is a key intermediate in the biosynthetic pathways to generate antitumor taxanes. Molecular modeling using the Monte Carlo protocol, followed by density functional theory (DFT) geometry optimization employing the hybrid functionals B3LYP and B3PW91, both with the DGDZVP basis set, secured the configuration of 3 as followed from the good agreement between the calculated and experimental vibrational circular dichroism spectra. Similar DFT calculations allowed determining the absolute configuration of (+)-(1R,4R,5R,8S,9S,11S,12R,15R)-1,15:4,5:8,9-triepoxyphomactane (9), which surprisingly derives from epoxidation of the second minimum energy conformer of 3.

Absolute configuration of cembrane diterpenoids from Bursera multijuga.

The stems of Bursera multijuga afforded (-)-(1S,3E,7R,8R,11E)-7,8-epoxycembra-3,11-dien-1-ol (1) and its acetate 2, together with cembrene A (3), nephthenol (4), and cembrenol (5). The structures of 1 and 2 were elucidated by 1D and 2D NMR, HRESIMS, and X-ray diffraction. The conformational preference of flexible 1 was studied by molecular modeling at the DFT B3LYP/DGDZVP level of theory. Good agreement between calculated and experimental vibrational circular dichroism curves established the absolute configuration of 1. This is the first time that cembrane derivatives have been isolated from the genus Bursera.

A new bisabolene from Stevia tomentosa.

The new sesquiterpene (1R,2R,3R,6R,7S)-1-acetoxy-2,3-dihydroxy-2,3-dihydrobisabolene (3) together with ten known terpenes and three known flavonoids were isolated from the aerial parts and from the roots of Stevia tomentosa. The structure of 3 follows from spectral studies, the relative chirality at C-3 follows from 1H NMR coupling constants comparison with the corresponding calculated values obtained by applying a generalized Karplus-type relationship to the dihedral angles of model compounds, and the absolute configuration is assumed in analogy to known (2R,3R,6R,7S)-2,3-epoxy-2,3-dihydrobisabolen-1-one (2).

Absolute configuration of podophyllotoxin related lignans from Bursera fagaroides using vibrational circular dichroism.

The ethanol extract from the dried exudate of Bursera fagaroides (Burseraceae) showed significant cytotoxic activity in the HT-29 (human colon adenocarcinoma) test system. The extract provided four podophyllotoxin related lignans, identified as (7'R,8R,8'R)-(-)-deoxypodophyllotoxin (3), (7'R,8R,8'R)-(-)-morelensin (4), (8R,8'R)-(-)-yatein (5), and (8R,8'R)-(-)-5'-desmethoxyyatein (6), whose spectroscopic and chiroptical properties were compared with those of (7R,7'R,8R,8'R)-(-)-podophyllotoxin (1) and its acetyl derivative (2). Their absolute configurations were assigned by comparison of the vibrational circular dichroism spectra of 1 and 3 with those obtained by density functional theory calculations.

Antifeedant and cytotoxic activity of longipinane derivatives.

The polyoxygenated longipinane derivatives 1- 8 were tested as antifeedant compounds against the herbivorous insects Spodoptera littoralis, Rhopalosiphum padi, and Myzus persicae. Compounds 1-3 and 8 exhibited significant antifeedant activity against S. littoralis and M. persicae. The antifeedant activity against S. littoralis increased moderately after the C-8 hydroxy group in 3 was removed to afford 1 and increased strongly after the remaining two hydroxy groups were acetylated to afford 2. Compound 1 was active on M. persicae. Compounds 1, 3, and 4, with an unsaturated six-membered ring, exhibited an increase in post-ingestive effects on S. littoralis ranging from antifeedant in the case of 1 to toxic for compounds 3 and 4. These compounds did not have any phytotoxic effect on Lactuca sativa. When tested on a panel of tumoral cells, compounds 2 and 6 exhibited moderate selective cytotoxic effects on the p53 null lung carcinoma cells H1299, which were not affected by the drug paclitaxel. In addition, vibrational circular dichroism (VCD) was applied to the representative longipinene derivative 2 to verify its absolute configuration, and the sensitivity of the VCD methodology was evaluated by comparing spectra of the three diastereoisomers (4 R,5 S,7 R,9 R,10 R,11 R)-7,9-diacetyloxylongipin-2-en-1-one (2), (4 R,5 S,7 S,9 R,10 R,11 R)-7,9-diacetyloxylongipin-2-en-1-one, and (4 R,5 S,7 R,9 S,10 R,11 R)-7,9-diacetyloxylongipin-2-en-1-one.

Oxygenated verticillene derivatives from Bursera suntui.

Medium polarity fractions of the hexane extracts of the stems of Bursera suntui afforded six previously known (1-6) and four hitherto unknown verticillane derivatives: (1S,3Z,7S,8S,11S,12S)-(+)-7,8-epoxyverticill-3-en-12,20-diol (7), (1S,3Z,7S,8S,11S,12S)-(+)-7,8-epoxyverticill-3-en-12,20-diol 20-acetate (8), (1S,3Z,7S,11S,12S)-(+)-verticilla-3,8(19)-dien-7,12,20-triol (9), and (1S,3Z,7S,11S,12S)-(+)-verticilla-3,8(19)-dien-7,12,20-triol 20-acetate (10). Acetylation of 9 and 10 yielded (1S,3Z,7S,11S,12S)-(+)-verticilla-3,8(19)-dien-7,12,20-triol 7,20-diacetate (11), while hydrolysis of 8 gave 7. The structures and stereochemistry of 7-11 were established by spectroscopic analyses, particularly by 1D and 2D NMR spectra and HRESIMS. The conformational preferences of 7-11 were studied by molecular mechanics modelling employing the Monte Carlo protocol followed by B3LYP/DGDZVP DFT calculation, thus supporting the observed (1)H NMR NOESY cross peaks.

Absolute configuration of verticillane diterpenoids by vibrational circular dichroism.

Good agreement between theoretical and experimental vibrational circular dichroism curves of (1S,11S,12S)-(+)-verticilla-3E,7E-dien-12-ol (1) established the absolute configuration of this natural diterpene isolated from Bursera suntui. Molecular modeling of 1 was carried out using the Monte Carlo protocol followed by geometry optimization at the B3LYP 6-31G(d,p) level of theory. The 12-membered ring of 1 was found in a single preferred chair-chair-chair-chair conformation. In the six-membered ring a chair prevails over a distorted boat, and the C-OH bond rotation generates three predominant rotamers. Validation of the minimum energy conformation for 1 was achieved by comparison of theoretical and experimental infrared frequencies, vicinal 1H NMR coupling constants, and X-ray diffraction data. This study confirms that (+)-verticillol 1 isolated from Bursera species has the 1S,11S,12S absolute configuration that corresponds to the same enantiomeric series as verticillanes from Sciadopitys and Taxus, while verticillanes from Jackiella and Jungermannia have antipodal structures.

Verticillane derivatives from Bursera suntui and Bursera kerberi.

The stems of Bursera suntui afforded two new verticillane derivatives, (1S,3Z,7E,11S,12S)-(+)-verticilla-3,7-dien-12,20-diol (1) and (1S,3Z,7E,11S,12S)-(+)-verticilla-3,7-dien-12,20-diol 20-acetate (2), together with (1S,3E,7E,11R)-(+)-verticilla-3,7,12(18)-triene (3), (1R,3E,7E,11R,12Z)-(+)-verticilla-3,7,12-triene (4), (1R,7E,11Z)-(-)-verticilla-4(20),7,11-triene (5), and (1S,3E,7E,11S,12S)-(+)-verticilla-3,7-dien-12-ol (6). Compounds 3 and 4 are new enantiomerically pure natural products whose racemic mixtures, derived from synthetic approaches toward the taxane skeleton, were obtained previously. The stems of Bursera kerberi afforded the new (1S,3E,7E,11S,12R)-(+)-verticilla-3,7-dien-12-ol (7) together with 3-5. This is the first time that verticillane derivatives have been isolated from the genus Bursera. Their structures and stereochemistry were elucidated by 1D and 2D NMR data, including COSY, NOESY, HSQC, and HMBC experiments, while the absolute configuration was determined by comparison of the optical rotatory dispersion data with that of recently revised (1S,3E,7E,11S,12S)-(+)-verticilla-3,7-dien-12-ol (6), obtained from Sciadopitys verticillata, and those of (1R,3E,7E,11R,12R)-(-)-verticilla-3,7-dien-12-ol (8) and (1R,3E,7E,11R,12S)-(-)-verticilla-3,7-dien-12-ol (9), isolated from the liverwort Jackiella javanica. The conformational preferences of 1-7 were studied by molecular mechanics modeling employing the Monte Carlo protocol.