Eight new peltogynoids, named bougainvinones A-H (1-8), were obtained from the stem bark of Bougainvillea spectabilis. Their structures were elucidated by means of physical data (1D and 2D NMR, HRESIMS) and single-crystal X-ray crystallographic analyses. The peltogynoids, a rare type of modified flavonoids, are reported for the first time from this species of the genus Bougainvillea. All isolated compounds were evaluated for their cytotoxic effects against five cancer cell lines including KB, Hela S-3, HT-29, MCF-7, and HepG2. Among them, compound 7 showed cytotoxicity against five cancer cell lines with IC50 values in the 7.4-9.7 μM range, and compounds 2 and 3 exhibited cytotoxicity against the KB cell line with IC50 values of 6.6 and 9.0 μM.

Introduction: Natural curcuminoids isolated from turmeric (Curcuma longa L.) have been limited in number and the amount of substrates evaluated in semi-synthetic processes and biological tests. Currently, potent anticancer activities of curcuminoids have garnered increased attention such that a greater number of synthetic procedures of curcumin analogues have been developed for further biological evaluations. The fluorine substituent of fluorinated compounds is important for biological responses. However, natural products bearing fluorine have rarely been found. In the study herein, we employed an aldol condensation between 4-hydroxy-3-methoxybenzaldehyde/3,4- difluorobenzaldehyde and pentane-2,4-dione to synthesize the desired curcumin (Cur) and 3,4- difluorinated curcumin (3,4-DFCur). Their half-maximal inhibitory concentration (IC50) values against HepG2, LU-1 and KB cancer cell lines were then assessed. Methods: Pentane-2,4-dione was converted to enol form by using B2O3 before carrying out C-C coupling reactions with benzaldehyde analogues under basic conditions. The water scavenger was added to the reaction to capture the produced water. The reaction mixture was stirred at 70 ◦C. The reaction progress was monitored by thin layer chromatography (TLC). Crude products were purified by flash column chromatography (CC; SiO2, eluent: HEX/EA = 9/1!7/3). The chemical structures of the desired products were elucidated by 1H, 13C-NMR, HSQC and MS spectra. The anticancer activities of Cur and 3,4- DFCur against HepG2, LU-1 and KB cancer cell lines were determined using MTT method. Results: Under reasonable reaction conditions, the yields for the coupling reactions were 53 and 72% for Cur and 3,4-DFCur, respectively. The stable enol tautomer of 1,3-diketone and the trans-configuration in a seven-carbon chain of product skeletons were assigned by 1H-NMR spectra. All synthesized products showed anticancer activities, with Cur exhibiting higher inhibitory activities when compared with 3,4-DFCur. Cur and 3,4-DFCur are Michael Acceptors; their cytotoxic activities could be attributed to the inhibition of glutathione S-transferase, a detoxification enzyme, by forming glutathionyl adducts. The decreased inhibitory capacities of 3,4-DFCur were due to the effect of fluorine which results in the unfavorable formation of reactive radicals and an increase in lipophilicity. Conclusions: Curcumin and 3,4-difluorinated curcumin were completely synthesized in 53% and 72% yields. The synthetic procedure is applicable for synthesizing curcumin derivatives bearing various substituents on the aromatic rings, i.e., not limited to methoxy (-OCH3) and hydroxy (- OH) groups. Unexpectedly, the presence of fluorines in 3,4-DFCur led to lower cytotoxic activities against cancer cell lines. Our results provide greater insight on the structure-activity relationship of curcumin analogues against cancer cell lines.

Euphorbia tirucalli has not been chemically studied much in Vietnam. This research described the isolation and elucidation of compounds isolated from the plant collected in Binh Thuan. Multiple chromatographic methods were applied, including normal phase silica gel column chromatography and thin-layer chromatography. Seven compounds were isolated and their chemical structures were elucidated by spectroscopic analysis as well as comparing their data with the ones in the literature. They are arjunolic acid (1), eriodictyol (2), quercitrin (3), afzelin (4), scopoletin (5), 3,3′,4- trimethylellagic acid (6), and gallic acid (7). Among them, compound 1 a major component was isolated for the first time in Euphorbia genus, while three compounds 2, 4, and 5 were isolated from this species for the first time.

No abstract

Introduction: The survival rate of oral cancer, like other types of cancers, has not been improved regardless of the early diagnosis and the introduction of advanced therapies. Treatment for oral cancer includes surgery, radiation therapy, and chemotherapy. However, the effectiveness has been limited due to recurrence and undesirable side effects. Metabolites from plant sources have been shown to be relatively less toxic and thus are considered as potential anti-cancer agents. Interestingly, curcumin isolated from the rhizome of Curcuma longa L. possesses broad-spectrum bioactivities. We focused on the synthesis of curcumin-based analogs bearing -OH/-OCH3/-F groups on the phenyl rings in our continuous efforts to search for curcumin-based anti-cancer agents. The synthesized compounds were subsequently evaluated for the cytotoxic activities against KB cancer cell line (an epidermal carcinoma of the mouth). Methods: The desired curcuminoids were synthesized via aldol reactions between benzaldehyde derivatives and pentane-2,4-dione using n-butylamine as a catalyst. Structures were distinguished by NMR and MS spectra. The cytotoxic activity against KB was determined through the half-maximal inhibitory concentration (IC50, mM). Results: Six curcumin analogs (1-6) were successfully synthesized in a yield of 48-76%. The 3- hydroxy/fluoro curcumin analogs (3, IC50 = 15.61 0.13 mM; 6, IC50 = 22.65 1.76 mM) exhibited better anti-cancer activities when compared to curcumin (1, IC50 = 33.35 2.66 mM), whereas the para-fluoro substitution patterns displayed lower inhibitory activities (4, 5) against KB cancer cell line. Conclusions: The synthetic yields are dependent on the position and nature of substituents in aromatic rings. The presence of electron-donating groups gives products (1-3) in lower yields when compared to those (4-6) prepared from fluorinated benzaldehydes as starting materials. The curcuminoids bearing -OH groups at para-positions in aromatic rings (1, 2) can be responsible for better inhibition of cell growth, whereas the fluoro-substituted compounds (4, 5) make a negative contribution to inhibitory activity. Furthermore, the contributions -OH/-F groups at meta-position in aromatic rings of (3, 6) on the cytotoxicity against KB are remarkable and firstly reported in our findings.