Convenient Preparation, Thermal Properties and X-ray Structure Determination of 2,3-Dihydro-5,6,7,8-tetranitro-1,4-benzodioxine (TNBD): A Promising High-Energy-Density Material

2,3-dihydro-5,6,7,8-tetranitro-1,4-benzodioxine (TNBD), molecular formula = C8H4N4O10, is a completely nitrated aromatic ring 1,4-benzodioxane derivative. The convenient method of TNBD synthesis was developed (yield = 81%). The detailed structure of this compound was investigated by X-ray crystallography. The results of the thermal analysis (TG) obtained with twice re-crystallized material revealed the onset at 240 °C (partial sublimation started) and melting at 286 °C. The investigated material degraded completely at 290-329 °C. The experimental density of 1.85 g/cm3 of TNBD was determined by X-ray crystallography. The spectral properties of TNBD (NMR, FT-IR and Raman) were explored. The detonation properties of TNBD calculated by the EXPLO 5 code were slightly superior in comparison to standard high-energy material-tetryl (detonation velocity of TNBD-7727 m/s; detonation pressure-278 kbar; and tetryl-7570 m/s and 226.4 kbar at 1.614 g/cm3, or 260 kbar at higher density at 1.71 g/cm3. The obtained preliminary results might suggest TNBD can be a potential thermostable high-energy and -density material (HEDM).

Total Synthesis of (-)-Amovillosumin A and Structure Correction of (-)-Amovillosumin C Using Chemical Synthesis

Norlignans are a rare class of natural products isolated from a diverse range of plant species, many of which have interesting biological activities including antibacterial, antioxidant, phytotoxic, platelet aggregation inhibitory effects, and more. Isolated from Amomum villosum (Amomi Fructus), amovillosumins A (1) and C (3) are norlignans which were of interest to synthesize, due to their interesting bioactivities, specifically their ability to increase stimulation of glucagon-like peptide-1 (GLP-1) secretion. In this research, key intermediate 15 was used to stereoselectively synthesize (7R,8R)-amovillosumins A (1) and C (3). The developed method includes a Mitsunobu coupling, a modified rhodium-catalyzed Miyaura arylation, and an acid-catalyzed cyclization in key bond-forming steps. After synthesis, the structure of 1 was confirmed, but it was revealed that the benzodioxane-containing structure of amovillosumin C (3) that had been proposed in the literature was incorrect. Thus, with further investigation a structure correction of 3 was achieved by synthesis, the correct structure being 8-O-4'-oxynorlignan.

Intramolecular Ni-catalyzed reductive coupling enables enantiodivergent synthesis of linoxepin

A nickel-catalyzed reductive tandem cyclization of the elaborated β-bromo acetal with a dibenzoxepin scaffold was invented to strategically construct the remaining two rings in linoxepin. The generated diasterodivergent intermediates could be easily converted to both enantiomers of this unique cyclolignan molecule via facile oxidations, thus realizing enantiodivergent total synthesis of linoxepin for the first time.

Indole-Fused Benzoxepine Synthesis via Visible-Light-Driven Aerobic Dehydrogenative [5 + 2] Annulation

A photocatalyzed oxidative dehydrogenative annulation between 2-(1H-indol-2-yl)phenols and alkenylphenols is presented. Various indole-fused benzoxepines can be obtained at room temperature using atom-efficient strategies. This method not only avoids the use of stoichiometric amounts of oxidants but also exhibits excellent atom economy by generating H2O as the only theoretical byproduct.

Lignin, the Lignification Process, and Advanced, Lignin-Based Materials

At a time when environmental considerations are increasingly pushing for the application of circular economy concepts in materials science, lignin stands out as an under-used but promising and environmentally benign building block. This review focuses (A) on understanding what we mean with lignin, i.e., where it can be found and how it is produced in plants, devoting particular attention to the identity of lignols (including ferulates that are instrumental for integrating lignin with cell wall polysaccharides) and to the details of their coupling reactions and (B) on providing an overview how lignin can actually be employed as a component of materials in healthcare and energy applications, finally paying specific attention to the use of lignin in the development of organic shape-memory materials.

New and promising type of leukotriene B4 (LTB4) antagonists based on the 1,4-benzodioxine structure

New leukotriene B4 (LTB4) antagonists have been synthesized that can be considered as potential anti-inflammatory drugs. Structures containing the dioxygenated nucleus of 1,4-benzodioxine constitute a potential group of leukotriene B4 (LTB4) antagonists. The objective of this study was to access efficient and selective LTB4 antagonists as a way to elucidate the role of LTB4 in inflammatory processes and therefore allow the development of new types of structures based on 1,4-benzodioxine. Forty-one new 1,4-benzodioxine molecules substituted at different positions of the heterocyclic nucleus were synthesized to determine the minimum structural requirements by studying structure-activity relationships. Eighteen of them were tested in vitro and in vivo for their anti-inflammatory activity related to the antagonist character of LTB4. Pharmacological tests have shown satisfactory in vitro activity for compounds 24b, 24c and 24e with IC50's of 288, 439, 477 nM respectively. The results of the in vivo tests, carried out with the compound that presented greater activity in the in vitro tests 24b, have shown significant anti-inflammatory properties.

Total synthesis of linoxepin facilitated by Ni-catalyzed tandem reductive cyclization

A nickel-catalyzed reductive cyclization was developed to construct the tricyclic core embedded in linoxepin, a cyclolignan with a unique benzoxepin ring. The generated diasterodivergent acetals could be converted to the...

Origin and Function of Structural Diversity in the Plant Specialized Metabolome

The plant specialized metabolome consists of a multitude of structurally and functionally diverse metabolites, variable from species to species. The specialized metabolites play roles in the response to environmental changes and abiotic or biotic stresses, as well as in plant growth and development. At its basis, the specialized metabolism is built of four major pathways, each starting from a few distinct primary metabolism precursors, and leading to distinct basic carbon skeleton core structures: polyketides and fatty acid derivatives, terpenoids, alkaloids, and phenolics. Structural diversity in specialized metabolism, however, expands exponentially with each subsequent modification. We review here the major sources of structural variety and question if a specific role can be attributed to each distinct structure. We focus on the influences that various core structures and modifications have on flavonoid antioxidant activity and on the diversity generated by oxidative coupling reactions. We suggest that many oxidative coupling products, triggered by initial radical scavenging, may not have a function in se, but could potentially be enzymatically recycled to effective antioxidants. We further discuss the wide structural variety created by multiple decorations (glycosylations, acylations, prenylations), the formation of high-molecular weight conjugates and polyesters, and the plasticity of the specialized metabolism. We draw attention to the need for untargeted methods to identify the complex, multiply decorated and conjugated compounds, in order to study the functioning of the plant specialized metabolome.

Discovery of inhibitors of Pseudomonas aeruginosa virulence through the search for natural-like compounds with a dual role as inducers and substrates of efflux pumps

Multidrug efflux pumps are ancient elements encoded in every genome, from bacteria to humans. In bacteria, in addition to antibiotics, efflux pumps extrude a wide range of substrates, including quorum sensing signals, bacterial metabolites, or plant-produced compounds. This indicates that their original functions may differ from their recently acquired role in the extrusion of antibiotics during human infection. Concerning plant-produced compounds, some of them are substrates and inducers of the same efflux pump, suggesting a coordinated plant/bacteria coevolution. Herein we analyse the ability of 1243 compounds from a Natural Product-Like library to induce the expression of P. aeruginosa mexCD-oprJ or mexAB-oprM efflux pumps' encoding genes. We further characterized natural-like compounds that do not trigger antibiotic resistance in P. aeruginosa and that act as virulence inhibitors, choosing those that were not only inducers but substrates of the same efflux pump. Four compounds impair swarming motility, exotoxin secretion through the Type 3 Secretion System (T3SS) and the ability to kill Caenorhabditis elegans, which might be explained by the downregulation of genes encoding flagellum and T3SS. Our results emphasize the possibility of discovering new anti-virulence drugs by screening natural or natural-like libraries for compounds that behave as both, inducers and substrates of efflux pumps.

Exploring synthetic and therapeutic prospects of new thiazoline derivatives as aldose reductase (ALR2) inhibitors

Inhibition of aldose reductase (ALR2) by using small heterocyclic compounds provides a viable approach for the development of new antidiabetic agents. With our ongoing interest towards aldose reductase (ALR2) inhibition, we have synthesized and screened a series of thiazoline derivatives (5a–k, 6a–f, 7a–1 & 8a–j) to find a lead as a potential new antidiabetic agent. The bioactivity results showed the thiazoline-based compound 7b having a benzyl substituent and nitrophenyl substituent-bearing compound 8e were identified as the most potent molecules with IC₅₀ values of 1.39 ± 2.21 μM and 1.52 ± 0.78 μM respectively compared with the reference sorbinil with an IC₅₀ value of 3.14 ± 0.02 μM. Compound 7b with only 23.4% inhibition for ALR1 showed excellent selectivity for the targeted ALR2 to act as a potential lead for the development of new therapeutic agents for diabetic complications.

Inhibition of aldose reductase (ALR2) by using small heterocyclic compounds provides a viable approach for the development of new antidiabetic agents.

Tetraaquabis(2,3-dihydro-1,4-benzodioxine-2-carboxylato)calcium(II)

In the title coordination compound, the metal ion is bonded to two monodentate carboxyl­ate groups and four water mol­ecules.

The acid–base reaction of 1,4-benzodioxane 2-carb­oxy­lic acid with calcium carbonate furnished the centrosymmetric title compound, [Ca(C₉H₇O₄)₂(H₂O)₄], in which the metal ion is octa­hedrally coordinated by two monodentate 1,4-benzodioxane 2-carboxyl­ate ligands and four water mol­ecules. In the crystal, O—H⋯O and C—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional network.

Controllable synthesis of 2- and 3-aryl-benzomorpholines from 2-aminophenols and 4-vinylphenols

We present herein a method for the controllable synthesis of 3-aryl-benzomorpholine and 2-aryl-benzomorpholine cycloadducts via cross-coupling/annulation between electron-rich 2-aminophenols and 4-vinylphenols. Molecular oxygen was successfully used in the reaction as the terminal oxidant and the complete inversion of chemoselectivity was achieved by the adjustment of the solvents and bases at room temperature.

Light-Promoted Nickel Catalysis: Etherification of Aryl Electrophiles with Alcohols Catalyzed by a NiII -Aryl Complex

A highly effective C-O coupling reaction of (hetero)aryl electrophiles with primary and secondary alcohols is reported. Catalyzed by a Ni^II -aryl complex under long-wave UV (390-395 nm) irradiation in the presence of a soluble amine base without any additional photosensitizer, the reaction enables the etherification of aryl bromides and aryl chlorides as well as sulfonates with a wide range of primary and secondary aliphatic alcohols, affording synthetically important ethers. Intramolecular C-O coupling is also possible. The reaction appears to proceed via a Ni^I -Ni^III catalytic cycle.

1,4-Benzodioxane, an evergreen, versatile scaffold in medicinal chemistry: A review of its recent applications in drug design

1,4-Benzodioxane has long been a versatile template widely employed to design molecules endowed with diverse bioactivities. Its use spans the last decades of medicinal chemistry until today concerning many strategies of drug discovery, not excluding the most advanced ones. Here, more than fifty benzodioxane-related lead compounds, selected from recent literature, are presented showing the different approaches with which they have been developed. Agonists and antagonists at neuronal nicotinic, α₁ adrenergic and serotoninergic receptor subtypes and antitumor and antibacterial agents form the most representative classes, but a variety of other biological targets are addressed by benzodioxane-containing compounds.

Molecular docking, quantum chemical computational and vibrational studies on bicyclic heterocycle "6-nitro-2,3-dihydro-1,4-benzodioxine": Anti-cancer agent

The heterocyclic aromatic compounds are primarily used to make pharmaceutical and agrochemicals. In addition, these compounds can be chosen as antioxidants, corrosion inhibitors, electro and opto-electronic devices, polymer material, dye stuff, developers, etc. On the account of this, the heterocyclic aromatic 6-nitro-2,3-dihydro-1,4-benzodioxine (6N3DB) was chosen and the structure is optimized to predict the important properties of it. The structural parameters such as bond length and bond angle have been obtained by DFT/B3LYP/6-311++G(d,p) basis set to know the geometry and orientation of 6N3DB. The molecule has been characterized by FT-IR and FT-Raman spectroscopic techniques to predict the functional groups, vibrational modes and aromatic nature of 6N3DB. The chemical shifts of ¹H and ¹³C have been obtained experimentally and compared with the theoretical data. The parameters such as the band gap between HOMO-LUMO orbitals, λ_max, and electron transition probability in frontier orbitals have been estimated to know the NLO and corrosion inhibition activity. HOMO-LUMO orbital diagram has been obtained for different energy levels and their band gap energies have been compared with UV-vis band gap values. The chemical significance of the molecule has been explained using ELF, LOL, and RDG. The binding energy and intermolecular energy values indicate that the title compound possesses anti-cancer property through hydrolase inhibition activity.

Radical coupling reactions of piceatannol and monolignols: A density functional theory study

Recent experimental work has revealed that the hydroxystilbene piceatannol can function as a monomeric unit in the lignification of palm fruit endocarp tissues. Results indicated that piceatannol homo-couples and cross-couples with monolignols through radical reactions and is integrally incorporated into the lignin polymer. The current work reports on the thermodynamics of the proposed reactions using density functional theory calculations. The results indicated that, in general, the energetics of both homo-coupling and cross-coupling are not dissimilar from those of the monolignol coupling, demonstrating the compatibility of piceatannol with the lignification process. Moreover, the DFT methods appear to predict the correct courses of post-coupling rearomatization reactions.

Directed Evolution of P450 BM3 towards Functionalization of Aromatic O-Heterocycles

The O-heterocycles, benzo-1,4-dioxane, phthalan, isochroman, 2,3-dihydrobenzofuran, benzofuran, and dibenzofuran are important building blocks with considerable medical application for the production of pharmaceuticals. Cytochrome P450 monooxygenase (P450) Bacillus megaterium 3 (BM3) wild type (WT) from Bacillus megaterium has low to no conversion of the six O-heterocycles. Screening of in-house libraries for active variants yielded P450 BM3 CM1 (R255P/P329H), which was subjected to directed evolution and site saturation mutagenesis of four positions. The latter led to the identification of position R255, which when introduced in the P450 BM3 WT, outperformed all other variants. The initial oxidation rate of nicotinamide adenine dinucleotide phosphate (NADPH) consumption increased ≈140-fold (WT: 8.3 ± 1.3 min-1; R255L: 1168 ± 163 min-1), total turnover number (TTN) increased ≈21-fold (WT: 40 ± 3; R255L: 860 ± 15), and coupling efficiency, ≈2.9-fold (WT: 8.8 ± 0.1%; R255L: 25.7 ± 1.0%). Computational analysis showed that substitution R255L (distant from the heme-cofactor) does not have the salt bridge formed with D217 in WT, which introduces flexibility into the I-helix and leads to a heme rearrangement allowing for efficient hydroxylation.

Stereoselective Total Synthesis of (+)-Aristolactam GI

Aristolactams are an important subgroup of aporphinoids, which all share a common phenanthrene chromophore motif that is thought to be responsible for the range of interesting physicochemical and biological properties exhibited by these compounds. Among all of the aristolactams discovered, (+)-aristolactam GI displays a unique structural feature of having the aristolactam scaffold linked via a benzodioxane ring to a phenyl propanoid unit, resulting in the compound being an aporphinoid-lignan hybrid. The synthesis of (+)-aristolactam GI was achieved first by synthesis of an orthogonally protected aristolactam, which was prepared using a Suzuki/aldol cascade to convert a differentially protected isoindolin-1-one to the required phenanthrene. The required enantiopure phenyl propanoid unit was prepared from readily available ( R)-methyl lactate. A selective Mitsunobu reaction was used to combine these two key fragments, prior to the formation of the linking benzodioxane in the final step. The absolute stereochemistry of the natural product was confirmed to be 7' S, 8' S.

A versatile catalyst system for enantioselective synthesis of 2-substituted 1,4-benzodioxanes

We report the synthesis of enantiomerically enriched 1,4-benzodioxanes containing alkyl, aryl, heteroaryl, and/or carbonyl substituents at the 2-position. The starting 1,4-benzodioxines were readily synthesized via ring closing metathesis using an efficient nitro-Grela catalyst at ppm levels. Excellent enantioselectivities of up to 99:1 er were obtained by using the versatile catalyst system [Ir(cod)Cl]2/BIDIME-dimer in the asymmetric hydrogenation of 2-substituted 1,4-benzodioxines. Furthermore, DFT calculations reveal that the selectivity of the process is controlled by the protonation step; and coordinating groups on the substrate may alter the interaction with the catalyst, resulting in a change in the facial selectivity.

1,4-Benzodioxane Lignans: An Efficient, Asymmetric Synthesis of Flavonolignans and Study of Neolignan Cytotoxicity and Antiviral Profiles

1,4-Benzodioxane lignans are a class of bioactive compounds that have received much attention through the years. Herein research pertaining to both 1,4-benzodioxane flavonolignans and 1,4-benzodioxane neolignans is presented. A novel synthesis of both traditional 1,4-benzodioxane flavonolignans and 3-deoxyflavonolignans is described. The antiviral and cytotoxic activities of 1,4-benzodioxane neolignans were then investigated; eusiderins A, B, G, and M, deallyl eusiderin A, and nitidanin, which contain the 1,4-benzodioxane motif but lack the chromanone motif found in the known antiviral flavonolignans, were tested. Notably, it was found that all eusiderin 1,4-benzodioxane neolignans exhibited greater antiviral activity than the potent and well-known silybin flavonolignans. While most modifications of the C-1' side chain did not significantly alter the cytotoxicity or antiviral activity, eusiderin M and nitidanin, which contain an allylic alcohol side chain, had lower cytotoxicity. All the eusiderins had similar antiviral activities, with eusiderin B having the best selectivity index. These results show that the chromanone moiety of the flavonolignans is not essential for bioactivity.

Modular Synthesis and Biological Investigation of 5-Hydroxymethyl Dibenzyl Butyrolactones and Related Lignans

Dibenzyl butyrolactone lignans are well known for their excellent biological properties, particularly for their notable anti-proliferative activities. Herein we report a novel, efficient, convergent synthesis of dibenzyl butyrolactone lignans utilizing the acyl-Claisen rearrangement to stereoselectively prepare a key intermediate. The reported synthetic route enables the modification of these lignans to give rise to 5-hydroxymethyl derivatives of these lignans. The biological activities of these analogues were assessed, with derivatives showing an excellent cytotoxic profile which resulted in programmed cell death of Jurkat T-leukemia cells with less than 2% of the incubated cells entering a necrotic cell death pathway.

Lignans: A Chemometric Analysis

The physicochemical properties of classical lignans, neolignans, flavonolignans and carbohydrate-lignan conjugates (CLCs) were analysed to assess their ADMET profiles and establish if these compounds are lead-like/drug-like and thus have potential to be or act as leads in the development of future therapeutics. It was found that while no studied compounds were lead-like, a very large proportion (>75%) fulfilled all the requirements to be deemed as present in drug-like space and almost all compounds studied were in the known drug space. Principal component analysis was an effective technique that enabled the investigation of the relationship between the studied molecular descriptors and was able to separate the lignans from their sugar derivatives and flavonolignans, primarily according to the parameters that are considered when defining chemical space (i.e., number of hydrogen bond donors, acceptors, rotatable bonds, polar surface area and molecular weight). These results indicate that while CLCs and flavonolignans are less drug-like, lignans show a particularly high level of drug-likeness, an observation that coupled with their potent biological activities, demands future pursuit into their potential for use as therapeutics.

How do reaction conditions affect the enantiopure synthesis of 2-substituted-1,4-benzodioxane derivatives?

Several biologically active compounds structurally include the enantiopure 2-substituted-1,4-benzodioxane scaffold. The straightforward racemization that affects reactions involving most of the common chemical reactives is thus a crucial issue. The developing of a completely stereo-controlled synthetic route that does not affect the enantiomeric excess is consequently mandatory. It is also important to set up a reliable chiral HPLC method, able to follow the reaction, and to improve the synthetic performances. Here, we report the chiral investigation of two different synthons, we specifically evaluated the synthetic pathways that could be run in order to afford them, avoiding the racemization processes, which could normally occur in basic conditions. In addition, we developed peculiar chiral HPLC methods in order to resolve the enantiomers, define the enantiomeric excess, and fully characterize these compounds.

Dual photoredox and nickel-catalyzed desymmetric C–O coupling reactions: visible light-mediated enantioselective synthesis of 1,4-benzodioxanes

Chiral 2,2′-bipyridine ligands are key to success in an enantioselective desymmetric C–O cross coupling reaction via dual visible light photoredox and nickel catalysis, resulting in chiral 1,4-benzodioxanes under mild reaction conditions.

Natural Products with Heteroatom-Rich Ring Systems

This review focuses on all known natural products that contain a "heteroatom-rich" ring system, specifically a five-, six- or seven-membered ring that contains three or more heteroatoms. The isolation and biological activity of these natural products is discussed, along with the biosynthetic processes that Nature employs to assemble these rare heterocyclic frameworks.

Recent advances in research on lignans and neolignans

Covering: 2009 to 2015Lignans and neolignans are a large group of natural products derived from the oxidative coupling of two C6-C3 units. Owing to their biological activities ranging from antioxidant, antitumor, anti-inflammatory to antiviral properties, they have been used for a long time both in ethnic as well as in conventional medicine. This review describes 564 of the latest examples of naturally occurring lignans and neolignans, and their glycosides in some cases, which have been isolated between 2009 and 2015. It comprises the data reported in more than 200 peer-reviewed articles and covers their source, isolation, structure elucidation and bioactivities (where available), and highlights the biosynthesis and total synthesis of some important ones.

Accumulation and Secretion of Coumarinolignans and other Coumarins in Arabidopsis thaliana Roots in Response to Iron Deficiency at High pH

Root secretion of coumarin-phenolic type compounds has been recently shown to be related to Arabidopsis thaliana tolerance to Fe deficiency at high pH. Previous studies revealed the identity of a few simple coumarins occurring in roots and exudates of Fe-deficient A. thaliana plants, and left open the possible existence of other unknown phenolics. We used HPLC-UV/VIS/ESI-MS(TOF), HPLC/ESI-MS(ion trap) and HPLC/ESI-MS(Q-TOF) to characterize (identify and quantify) phenolic-type compounds accumulated in roots or secreted into the nutrient solution of A. thaliana plants in response to Fe deficiency. Plants grown with or without Fe and using nutrient solutions buffered at pH 5.5 or 7.5 enabled to identify an array of phenolics. These include several coumarinolignans not previously reported in A. thaliana (cleomiscosins A, B, C, and D and the 5'-hydroxycleomiscosins A and/or B), as well as some coumarin precursors (ferulic acid and coniferyl and sinapyl aldehydes), and previously reported cathecol (fraxetin) and non-cathecol coumarins (scopoletin, isofraxidin and fraxinol), some of them in hexoside forms not previously characterized. The production and secretion of phenolics were more intense when the plant accessibility to Fe was diminished and the plant Fe status deteriorated, as it occurs when plants are grown in the absence of Fe at pH 7.5. Aglycones and hexosides of the four coumarins were abundant in roots, whereas only the aglycone forms could be quantified in the nutrient solution. A comprehensive quantification of coumarins, first carried out in this study, revealed that the catechol coumarin fraxetin was predominant in exudates (but not in roots) of Fe-deficient A. thaliana plants grown at pH 7.5. Also, fraxetin was able to mobilize efficiently Fe from a Fe(III)-oxide at pH 5.5 and pH 7.5. On the other hand, non-catechol coumarins were much less efficient in mobilizing Fe and were present in much lower concentrations, making unlikely that they could play a role in Fe mobilization. The structural features of the array of coumarin type-compounds produced suggest some can mobilize Fe from the soil and others can be more efficient as allelochemicals.