Polyunsaturated fatty acid-derived chromones exhibiting potent antioxidant activity

Advances in the site-selective C-5, C-3 and C-2 functionalization of chromones via sp2 C-H activation

In this work, site-selective C-H activation at C-5, C-3 and C-2 positions of chromones for the introduction of structural diversity to the chromone scaffold was studied. The keto group of the chromone moiety acts as the directing group for the selective functionalization of chromones at the C-5 position. Furthermore, the C-H functionalization at the electron-rich C-3 position of the chromone can be achieved using electrophilic coupling partners. The C-H functionalization at the C-2 position can be possible using nucleophilic coupling partners. The direct functionalization methods provide a better pathway for the generation of C-5, C-3 and C-2-substituted chromones with good atom economy than that of classical pre-functionalized reaction protocols.

In-vitro Chemopreventive Potential of a Chromone from Bomarea setacea (ALSTROEMERIACEAE) against Colorectal Cancer

Chemoprevention with natural products may provide important alternatives in the search for new drugs to treat cancer. Thus, the ethanol extract of Bomarea setacea and its secondary metabolite (chromone) were evaluated in-vitro in SW480 and SW620 human adenocarcinoma colon cells to identify a possible effect on cell growth, antiproliferative and/or proapoptotic activity. The ethanol extract did not show growth inhibition of these cell lines 48 h after treatment; besides, it required higher concentration and time to have an antiproliferative effect. On the other hand, although the chromone was not as active as the reference drug (5-FU), it displayed a greater selectivity, being 156-fold more selective against SW480 cells (SI => 100) and 255-fold against SW620 cells (SI => 86,9). Additionally, the chromone caused an important arrest in G2/M (44.18%) with an important accumulation in subG0/G1 phase in SW620 cells, inducing loss in mitochondrial membrane potential and damage in the cell membrane of both cell lines, with activation of caspase 3, suggesting an apoptotic process independent of ROS production and p53 activation.

Enzymatic studies with 3-oxa n-3 DPA

Cyclooxygenase-2 and several lipoxygenases convert polyunsaturated fatty acids into a large variety of products. During inflammatory processes, these enzymes form several distinct families of specialized pro-resolving lipid mediators possessing potent anti-inflammatory and pro-resolving effects. These mediators have attracted a great interest as leads in drug discovery and have recently been the subject of biosynthetic pathway studies using docosahexaenoic and n-3 docosapentaenoic acid as substrates. Herein we present enzymatic studies with cyclooxygenase-2 and 5-, 12- and 15-lipoxygenase enzymes using 3-oxa n-3 DPA as a synthetic mimic of n-3 docosapentaenoic acid. Structural elucidation based on data from RP-HPLC UV and LC/MS-MS experiments enabled the identification of novel enzymatically formed products. These findings constitute the basis for further biosynthetic studies towards understanding the mechanisms regulating substrate utilization in the biosynthesis of specialized pro-resolving lipid mediators.

Synthesis, molecular modelling studies and biological evaluation of new oxoeicosanoid receptor 1 agonists

The oxoeicosanoid receptor 1 (OXER1) is a member of the G-protein coupled receptors (GPCR) family, and is involved in inflammatory processes and oncogenesis. As such it is an attractive target for pharmacological intervention. The present study aimed to shed light on the molecular fundaments of OXER1 modulation using chemical probes structurally related to the natural agonist 5-oxo-ETE. In a first step, 5-oxo-ETE and its closely related derivatives (5-oxo-EPE and 4-oxo-DHA) were obtained by conducting concise and high-yielding syntheses. The biological activity of obtained compounds was assessed in terms of potency (EC₅₀) and efficacy (E_max) for arrestin recruitment. Finally, molecular modelling and simulation were used to explore binding characteristics of 5-oxo-ETE and derivatives with the aim to rationalize biological activity. Our data suggest that the tested 5-oxo-ETE derivatives (i) insert quickly into the membrane, (ii) access the receptor via transmembrane helices (TMs) 5 and 6 from the membrane side and (iii) drive potency and efficacy by differential interaction with TM5 and 7. Most importantly, we found that the methyl ester of 5-oxo-ETE (1a) showed even a higher maximum response than the natural agonist (1). In contrast, shifting the 5-oxo group into position 4 results in inactive compounds (4-oxo DHA compounds (3) and (3a)). All in all, our study provides relevant structural data that help understanding better OXER1 functionality and its modulation. The structural information presented herein will be useful for designing new lead compounds with desired signalling profiles.

Synthesis, Biological Investigation, and Structural Revision of Sielboldianin A

The two ar-bisabol sesquiterpenoids (+)-sielboldianin A (1) and (+)-sielboldianin B (2) were isolated from the stem bark of the plant Fraxinus sielboldiana and belong to a medicinally interesting class of natural products used in traditional Chinese medicine. Herein the total synthesis of the proposed structure of (+)-sielboldianin A (1) is reported using an organocatalyzed enantioselective bromolactonization protocol. X-ray analysis of a key intermediate together with specific rotation values and NOESY data of the synthesized product enabled the revision of the absolute configuration of the natural product (+)-sielboldianin A to (7 R,10 R). Studies on the antioxidant effects using two cell-based assays were conducted. These studies revealed that the enantiomer of 1 exhibited antioxidant effects with IC₅₀ values of 18 ± 3 μM in a cellular lipid peroxidation antioxidant activity assay. Moreover, (-)-1 showed strong protective effects against reactive oxygen species in a cell-based antioxidant activity assay (IC₅₀ = 31 ± 5 μM). In addition, the two ar-sesquiterpenoids (-)-boivinianin B and (-)-gossoronol showed no effect in either assay. No cytotoxic activity in the K562 cancer cell line was observed for the three sesquiterpenoids tested (IC₅₀ > 50 μM).

Synthetic manipulations of polyunsaturated fatty acids as a convenient strategy for the synthesis of bioactive compounds

The utilization of commercial polyunsaturated fatty acids in semi-syntheses of polyunsaturated natural products and derivatives has been reviewed.

Omega-3 polyunsaturated lipophenols, how and why?

Polyphenols and n-3 polyunsaturated fatty acids (PUFAs) are two classes of natural compounds, which have been highlighted in epidemiological studies for their health benefits. The biological activities of those two families of metabolites on oxidation, inflammation, cancer, cardiovascular and degenerative diseases have been reported in vitro and in vivo. On the other hand, chemical bonding between the two structures leading to n-3 lipophenol derivatives (or phenolipids) has been studied in numerous works over the last decade, and some examples could also be found from natural sources. Interest in lipophilization of phenolic structures is various and depends on the domain of interest: in food industry, the development of lipidic antioxidants could be performed to protect lipidic food matrix from oxidation. Whereas, on pharmaceutical purpose, increasing the lipophilicity of polar phenolic drugs could be performed to improve their pharmacological profile. Moreover, combining both therapeutic aspects of n-3 PUFAs and of polyphenols in a single lipophenolic molecule could also be envisaged. An overview of the synthesis and of the natural sources of n-3 lipophenols is presented here, in addition to their biological activities which point out in several cases the benefit of the conjugated derivatives.

Comparison of food antioxidants and iron chelators in two cellular free radical assays: strong protection by luteolin

Liver (HepG2) cells were incubated with 21 edible flavonoids, carotenoids, polyunsaturated fatty acid (PUFA) chromones, and metal chelators for 1 h, washed in PBS, and challenged in the cellular antioxidant activity (CAA) and the cellular lipid peroxidation antioxidant activity (CLPAA) assays. These microplate format assays assess the compounds' ability to protect against cytosolic peroxyl radicals (CAA) and induced membrane lipid peroxidation (CLPAA), respectively. Incubation encompassing a broad compound concentration range determined half-maximal inhibitory concentrations (IC(50)) by using sigmoidal curve fits. Overall, considering both assays, luteolin offered the greatest protection. The carotenoid astaxanthin offered only modest protection, whereas β-carotene was ineffective. Subtle structural differences between flavonoids were found to have amplified effects on protective abilities, and mechanisms of flavonoid antioxidant action are discussed. Membrane-permeable iron chelators (deferasirox and SIH) offered strong protective effects in CLPAA, but not in CAA, suggesting that CLPAA is dependent on membrane-associated free iron ions.

Synthesis of All-Z-1,6,9,12,15-octadecapenten-3-one, a vinyl ketone polyunsaturated marine natural product isolated from Callysponga sp

The synthesis of the marine natural product 1,6Z,9Z,12Z,15Z-octadecapentaen-3-one (1) has been achieved by two different routes starting from the ethyl esters of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), respectively. Using EPA ethyl ester as starting material the polyunsaturated vinyl ketone lipid 1 was obtained in 17% overall yield.

Stereoselective synthesis of protectin D1: a potent anti-inflammatory and proresolving lipid mediator

A convergent stereoselective synthesis of the potent anti-inflammatory, proresolving and neuroprotective lipid mediator protectin D1 (2) has been achieved in 15% yield over eight steps. The key features were a stereocontrolled Evans-aldol reaction with Nagao's chiral auxiliary and a highly selective Lindlar reduction of internal alkyne 23, allowing the sensitive conjugated E,E,Z-triene to be introduced late in the preparation of 2. The UV and LC/MS-MS data of synthetic protectin D1 (2) matched those obtained from endogenously produced material.