Fitoquímica Aplicada

Flavonoids are phenolic substances that appear to exert beneficial effects in several chronic diseases, including cancer. Structure-activity relationships of the cytotoxic activity of a series of flavonols and their 3-methyl ether derivatives established that 3′-hydroxy-3,4′-dimethoxyflavone (flavonoid 11) displayed strong cytotoxicity against human leukaemia cell lines (HL-60, U-937 and MOLT-3), and cells that over-express the anti-apoptotic proteins, Bcl-2 and Bcl-x, and against P-glycoprotein-overexpressing K-562/ADR cells. This compound induced G-M cell cycle arrest and it was a potent apoptotic inducer on HL-60, MOLT-3, U-937 and U-937/Bcl-2 cell lines. Cell death was (i) mediated by caspase activation, since it was prevented by the non-specific caspase inhibitor z-VAD-fmk and reduced by a selective caspase-9 inhibitor, (ii) associated with cytochrome c release, the dissipation of the inner mitochondrial membrane potential (ΔΨ) and the activation of the mitogen-activated protein kinase pathway and (iii) partially blocked by the inhibition of c-jun NH terminal kinases/stress activated protein kinases (JNK/SAPK) signalling and by the free-radical scavenger N-acetyl-L-cysteine.

In this study, we investigated the effects of synthetic 3′,4′-dibenzyloxyflavonol on viabilities of eight human tumor cells. It was cytotoxic against leukemia cells (HL-60, U-937, MOLT-3, K-562, NALM-6, Raji), with significant effects against P-glycoprotein-overexpressing K-562/ADR and Bcl-2-overexpressing U-937/Bcl-2 cells, but had no significant cytotoxic effects against quiescent or proliferating human peripheral blood mononuclear cells. The IC50 value for the leukemia HL-60 cells was 0.8 ± 0.1 μM. This indicates a 60–fold greater toxicity than the naturally occurring flavonol quercetin. Synthetic 3′,4′-dibenzyloxyflavonol induced S phase cell cycle arrest and was a potent apoptotic inducer in human leukemia cells. Cell death was (i) mediated by the activation and the cleavage of initiator and executioner caspases; (ii) prevented by the pan-caspase inhibitor z-VAD-fmk; (iii) associated with the release of cytochrome c and with the phosphorylation of members of the mitogen activated protein kinases including p38MAPK, JNK/SAPK and ERK, and (iv) independent of the generation of reactive oxygen species. The synthetic 3′,4′-dibenzyloxyflavonol is a potent cytotoxic compound against several human leukemia cells and might be useful in the development of new strategies in the fight against cancer.

Investigation of the aerial parts of two Spanish members of the Asteriscus alliance, Asteriscus graveolens subsp. stenophyllus and Asteriscus schultzii, afforded four new sesquiterpene lactones containing a humulene skeleton (1–4) and one new sesquiterpene lactone of the asteriscanolide type (5). Their chemical structures were determined on the basis of the HRMS and from 1D and 2D NMR spectroscopic studies. Both species showed different profiles of sesquiterpenoid constituents. A. schultzii did not show humulene or asteriscane sesquiterpenes, suggesting a resemblance to the genus Pallenis, another member of the Asteriscus alliance. A literature review on chemical isolates from the Asteriscus alliance supported the placement of A. schultzii in the genus Pallenis. The isolated components (1–5) were assessed for cytotoxicity against the HL-60 and MOLT-3 leukemia cell lines, with compound 1 showing activity in both biological assays (IC50 value range 4.1–5.4 μM).

New glycolipids that feature a carbohydrate/triazole/lipid hybrid architecture were readily produced by a combined multicomponent/click approach. The process comprises the use of the Ugi four‐component reaction to construct double‐lipidic scaffolds that have either alkyne or azide functionalities followed by conjugation to mono‐ and trisaccharides through a CuI‐catalyzed 1,3‐dipolar cycloaddition (click) process. The high chemical efficiency and feasibility of the overall procedure provides new opportunities for the rapid creation and biological screening of libraries of this unique class of Ugi/click glycolipids. Dynamic NMR experiments were performed to evaluate the free energy of activation related to the isomerization of the cis/trans amide bond in these compounds. This is the first time that such multicomponent and cycloaddition processes have been combined for the synthesis of glycolipids.

Flavonoids are polyphenolic compounds which display an array of biological activities and are considered potential antitumor agents. Here we evaluated the antiproliferative activity of selected synthetic flavonoids against human leukemia cell lines. We found that 4′-bromoflavonol (flavonol 3) was the most potent. This compound inhibited proliferation in a concentration-dependent manner, induced apoptosis and blocked cell cycle progression at the S phase. Cell death was found to be associated with the cleavage and activation of multiple caspases, the activation of the mitogen-activated protein kinase pathway and the up-regulation of two death receptors (death receptor 4 and death receptor 5) for tumor necrosis factor-related apoptosis-inducing ligand. Moreover, combined treatments using 4′-bromoflavonol and TRAIL led to an increased cytotoxicity compared to single treatments. These results provide a basis for further exploring the potential applications of this combination for the treatment of cancer.

The diversity-oriented synthesis of novel bis-spirostanic conjugates utilizing two different Ugi four-component reactions (Ugi-4CR) is described. Spirostanic steroids were functionalized with Ugi-reactive groups, that is, amines, isocyanides, and carboxylic acids, and next were subjected to multicomponent ligation approaches leading to bis-steroidal conjugates featuring pseudo-peptidic and heterocyclic linkage moieties. Both the classic Ugi-4CR and its hydrazoic acid variant were implemented, proving good efficiency for the ligation of isocyanosteroids to spirostanic acids and equatorial amines. Axially oriented amines showed poorer results, although model studies proved that chemical efficiency could be significantly improved while increasing reaction times. Overall, the method comprises the rapid generation of molecular diversity at the bis-steroid linkage moiety and, consequently, shows promise toward the production of combinatorial libraries of bis-spirostanes for biological screening.