Benzofuran Ring Research Articles

Benzofuran and Indole: Promising Scaffolds for Drug Development in Alzheimer's Disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no clinically accepted treatment to cure or halt its progression. The Food and Drug Administration has approved drugs (e.g., rivastigmine, donepezil, galantamine, and memantine) that at best provide marginal benefits, thus emphasizing the urgent need to explore other molecular entities as future drug candidates for AD. Looking at the wide pharmaceutical applications of heterocyclic compounds and particularly those containing benzofuran and indole ring systems, these molecular frameworks have drawn special attention from medicinal chemists for further evaluation in numerous diseases. This article focuses on the history and recent advances of benzofuran- and indole-based compounds as inhibitors of butyrylcholinesterase, acetylcholinesterase, γ-secretase, β-secretase, tau misfolding, and β-amyloid aggregation.

2-Hydroxy-4-(3\u2032-oxo-3\u2032H-benzofuran-2\u2032-yliden)but-2-enoic acid biosynthesis from dibenzofuran using lateral dioxygenation in a Pseudomonas putida strain B6-2 (DSM 28064)

BackgroundBenzofuran and its derivatives contain central pharmacophores and are important structures in medicinal chemistry. Chemical synthesis of benzofuran rings often requires expensive catalysts and stringent operational conditions. Biosynthesis is recognized as a promising way to save energy and produce valuable compounds. Dioxin biodegradation pathways can form several benzofuran derivatives, and these pathways may be a better choice for further synthesis of important biological compounds. 2-Hydroxy-4-(3′-oxo-3′H-benzofuran-2′-yliden)but-2-enoic acid (HOBB), a benzofuran derivative, can be biosynthesized from dibenzofuran (DBF) through co-metabolic degradation in a lateral dioxygenation pathway.ResultsEfficient biosynthesis of HOBB was observed using whole cells of Pseudomonas putida strain B6-2. After cultivation in LB medium containing biphenyl, the cells were suspended to an OD600 of 5 to conduct biosynthesis in the presence of 0.5-mM DBF at pH 7 for 8 h. The bacterial cells were used twice to degrade approximately 0.70-mM DBF, and in batch process, accumulated about 0.29-mM HOBB. HOBB could be easily purified from the reaction with ethyl acetate using the neutral-acid extraction method, and 13.58 ± 0.31 mg of HOBB was obtained from 22.49 ± 0.74-mg DBF with an overall production yield of 60.4% (w/w). The product HOBB, which is a yellow powder, could be detected and identified by LC–MS, GC–MS, and NMR.ConclusionsIn this study, a new biological route was developed to produce HOBB from DBF using whole cells of P. putida B6-2 (DSM 28064). The biosynthesis of HOBB may contribute to studies of the DBF lateral pathway and provide a new green route for synthesizing benzofuran derivatives with pharmacological activities.

Direct Synthesis of 2-Methylbenzofurans from Calcium Carbide and Salicylaldehyde p-Tosylhydrazones

A new methodology for the construction of methyl-substituted benzofuran rings from the reactions of calcium carbide with salicylaldehyde p-tosylhydrazones/2-hydroxyacetophenone p-tosylhydrazones is described. Various 2-methylbenzofurans and 2,3-dimethylbenzofurans could be obtained in satisfactory yield by using a cuprous chloride catalyst. The advantages of this protocol include the use of a readily available and easy-to-handle acetylene source and simple workup procedure.

A Natural Benzofuran from the Patagonic Aleurodiscus vitellinus Fungus has Potent Neuroprotective Properties on a Cellular Model of Amyloid-β Peptide Toxicity.

Alzheimer's disease (AD) is characterized by amyloid plaques that form due to an increase in amyloid-β peptide (Aβ) aggregation. One strategy in the search of new treatments for AD focuses on compounds that decrease Aβ accumulation. Compounds containing a benzofuran ring have been described to play an important role in decreasing Aβ-induced toxicity; however, only synthetic benzofurans have been tested thus far. The aim of the present study was to examine the in vitro neuroprotective properties of fomannoxin (Fx), a natural benzofuran isolated from cultures of the Andean-Patagonian fungi Aleurodiscus vitellinus, and evaluate its effect on Aβ peptide. We tested the effect of Fx at a wide concentration range (10-11-10-4 M) in PC-12 cells, and found the compound did not alter cellular viability. Fx also showed a concentration-dependent effect on the Aβ-induced toxicity in PC12 cells, showing viability above 100% at 10-6 M. We then measured the effect of Fx (10-7-10-5 M) on the frequency of cytosolic Ca2+ transients in rat hippocampal neurons at both acute and chronic (24 h) times. Acute incubation with Fx increased the frequency of cytosolic Ca2+ transients to values around 200%, whereas chronic incubation with Fx increased the frequency of Ca2+ transients. Finally, the Aβ-induced decrease in intracellular Ca2+ transients was prevented when Fx (10-6 M) was co-incubated with Aβ (5×10-6 M). The results suggest a potent neuroprotective effect of this naturally occurring benzofuran against Aβ peptide toxicity that could be mediated by an interference with it binding to plasma membrane, and lead Fx as new chemical entity to develop pharmacological tools against Aβ peptide neurotoxicity.

Germanium-Bridged 2-Phenylbenzoheteroles as Luminophores Exhibiting Highly Efficient Solid-State Fluorescence.

[1]Benzogermolo[3,2-b]indoles, [1]benzogermolo[3,2-b]benzofuran, [1]benzogermolo[3,2-b]benzothiophene, and [1]benzogermolo[3,2-b]benzothiophene-S,S-dioxide were synthesized from the corresponding 3-bromo-2-(2-bromophenyl)benzoheteroles and characterized. A comparison of the absorption spectra of the Ph2 Ge- and Ph2 Si-bridged 2-phenylindoles reveals that the Ge bridge has the effect of slightly widening the HOMO-LUMO energy gap of the bridged 2-phenylindole π-system with regard to the Si-bridged system. Replacement of the indole ring by benzofuran or benzothiophene rings induces blueshifts in the absorption spectrum, whereas the absorption spectrum of the benzothiophene-S,S-dioxide derivative was redshifted with respect to the indole derivative. These results are consistent with the changes in the HOMO-LUMO energy gaps calculated by using density functional theory. The Ph2 Ge-bridged indole, benzofuran, and benzothiophene-S,S-dioxide derivatives exhibit brilliant fluorescence in the violet-to-blue region with good-to-excellent quantum yields in toluene (λem =376-439 nm, Φ=0.62-0.99) and powder form (λem =401-451 nm, Φ=0.64-0.80).

Interrupting Base-Mediated Benzofuran Ring Transformation with Michael Acceptors.

A simple two-stage approach for the synthesis of 3-(2-arylbenzofuran-3-yl)propanoates and propanamides has been developed employing simple acrylates and acrylamides and readily available 3-aroylbenzofurans. The key step of this process involves a base-mediated ring opening of the 3-aroylbenzofurans and subsequent Michael addition of the resulting 1,3-dicarbonyl intermediate with acrylate/acrylamide, followed by the deformylation in one-pot. The resulting products undergo an acid-mediated dehydrative cyclization to arrive at these targets.

Synthesis of Flavonoid Derivatives of Cytisine. 5. Aminomethylation of 6-Hydroxyaurones

Aminomethylation of 6-hydroxy- and 6-hydroxy-7-methylaurones by the alkaloid cytisine was studied. It was shown that the aminomethylation of the 6-hydroxyaurones occurred at the 7-position of the benzofuran ring and at the 5-position if the 7-position was occupied.

Strong hydrogen bonded supramolecular architecture in a crystal of the {3-[2-(1,3-benzodioxol-5-yl)-7-methoxy-1-benzofuran-5-yl] propyl} diethylamine cation with the hydrogen bonded chloride hydrate anion (halides) assembly: X-ray structure, DFT calculations, Hirshfeld surface analysis

The crystal structure of {3-[2-(1,3-benzodioxol-5-yl)-7-methoxy-1-benzofuran-5-yl] propyl} diethylamine hydrohloride hydrate [C23H28NO4]+•[H2OCl]– is determined. The molecular geometrical parameters, frontier molecular orbital energies (HOMO, LUMO), their energy gap (ΔE), molecular electrostatic potential analysis of the compound are calculated by DFT/B3LYP at the 6-311G(d,p) level. The benzofuran and benzodioxo ring systems, except the diethylamine group, are essentially planar and a dihedral angle between the ring systems is 7.38(14)°. The compound crystallizes in the monoclinic space group P21/c, with a = 15.230(4) A, b = 11.418(2) A, c = 12.880(3) A, β = 94.56(3)°, V = 2232.8(9) A3, D calc = 1.297g/cm3, Z = 4. The hydrogen bonded Cl and H2O are self-assembled to form a supramolecular array of strong N–H…Cl and O–H…Cl bifurcated hydrogen bonds making tetramers which consist of a fused four-membered ring with a graph-set descriptor and a pseudo cyclic centrosymmetric R 2 2(8) ring motif. The hybrid dihalide-dihydrate clusters of [Cl2(H2O)2]2– are observed, too. The supramolecular crystal packing is consolidated by these bifurcated hydrogen bonds and the stacking of the sheet through strong π…π interactions. Moreover, the intra chain hydrogen bonds form intermolecular and intramolecular C–H…O hydrogen bonds, and the 1D supramolecular array is organized by C–H…π interactions. The contacts in the crystal structure are analyzed using the Hirshfeld surfaces computational method. The calculated geometrical parameters are in good agreement with the single crystal XRD data.

Design, stereoselective synthesis and computational calculations of novel hybrid compounds via Pauson-Khand reactions

A series of novel chiral hybrid compounds between benzofuran and bicyclic cyclopentenone and also benzothiophene and bicyclic cyclopentenone have been designed and synthesized. Chiral enynes derived from enantiomerically enriched homoallyl and homopropargyl alcohols were converted into bicyclic cyclopentenone structures by intramolecular Pauson-Khand reactions. This strategy provides a facile access to various bicyclic cyclopentenones substituted with benzofuran or benzothiophene ring systems in good yields. In addition to the experimental work, the ground state geometries of the hybrid compounds were optimized using Density Functional Theory applications at the B3LYP/6-31G(d,p) level in order to obtain information about the 3D geometries and electronic structure.

2-(5-Methyl-1-benzofuran-3-yl)-N-(2-phenylethyl)acetamide

The title compound, C19H19NO2, is non-planar with the phenyl ring of the phenethylacetamide residue inclined to the benzofuran ring system by 84.8 (3)°. The methyl group lies in the plane of the fused ring system [C—C—C—C torsion angle = −179.6 (3)°]. In the crystal, N—H...O hydrogen bonds link the molecules into chains along thea-axis direction. π–π stacking interactions with a centroid-to-centroid distances of 3.497 (3) Å further stabilize the structure, stacking the molecules alonga.

3-(1H-Indol-3-yl)-2-benzofuran-1(3H)-one

In the title compound, C16H11NO2, the benzofuran and indole ring systems are nearly orthogonal, subtending a dihedral angle of 86.55 (4)°. The crystal structure features an N—H...O hydrogen bond, which leads to the formation of chains propagating along the a-axis direction.

Total synthesis of natural products containing benzofuran rings

In this review, various approaches for the construction of benzofurans as an important moiety in different natural products during the total synthesis of the natural of products are underscored.

Emission pathway switching by solvent polarity: Facile synthesis of benzofuran-bipyridine derivatives and turn-on fluorescence probe for zinc ions

Bipyridine attached benzofuran derivatives were prepared by the cyclization of alkyne ortho-substituted phenols. Electronically different substituents, N,N-dibutylamino vs tert-butyl group, were attached on benzofuran rings. Depending on the polarity and pH of solvent environment, N,N-dialkylamino group participates in two distinctively different roles in emissive properties, i.e., ICT-type and PET-type behaviors. Upon capturing lone-pair electrons of N,N-dialkylamino groups by protonation, ratiometric blue-shift and complete turn-on behaviors were observed in THF and MeCN solution, respectively. Such peculiar behavior was further utilized to show turn-on sensing of zinc ions.

Crystal structure of vilazodone hydro-chloride methanol monosolvate.

In the title compound, C26H28N5O2+·Cl-·CH3OH {systematic name: 4-(2-carbamoyl-1-benzo-furan-5-yl)-1-[4-(5-cyano-1H-indol-3-yl)but-yl]piperazin-1-ium chloride methanol monosolvate}, the protonated piperazine ring adopts a chair conformation. The indole ring plane is nearly perpendicular to the benzo-furan ring system, with a dihedral angle of 85.77 (2)°. In the crystal, the organic cations, Cl- anions and methanol solvent mol-ecules are linked by classical N-H⋯O and N-H⋯Cl hydrogen bonds, and weak C-H⋯O and C-H⋯π inter-actions into a three-dimensional supra-molecular architecture.

Crystal structures of two new carbazole derivatives: 12-(4-nitro-phen-yl)-7-phenyl-sulfonyl-7H-benzofuro[2,3-b]carbazole and 2-methyl-4-(4-nitro-phen-yl)-9-phenyl-sulfonyl-9H-thieno[2,3-b]carbazole.

The title compounds, C30H18N2O5S, (I), and C27H18N2O4S2, (II), are carbazole derivatives with a phenyl-sulfonyl group and a nitro-phenyl group attached to the carbazole moiety in identical positions in both mol-ecules. A benzo-furan ring system in (I) and a methyl-thio-phene ring in (II) are fused with the respective carbazole moieties on the same sides. The mean plane of the carbazole ring system makes a dihedral angle of 3.17 (7)° with the benzo-furan ring system in (I) and a dihedral angle of 3.39 (11)° with the methyl-thio-phene ring in (II), implying that both fused units are essentially planar. The mean planes of the carbazole ring systems in both the compounds are almost orthogonal to the respective nitro-substituted phenyl rings, making dihedral angles of 75.64 (10) and 77.63 (12)° in compounds (I) and (II), respectively. In (I), the phenyl-sulfonyl ring system is positionally disordered with a refined occupancy ratio of 0.63 (2):0.37 (2). In both compounds, the mol-ecular structures are stabilized by intra-molecular C-H⋯O hydrogen bonds, generating S(6) ring motifs with the sulfone group O atoms. In the crystal of compound (I), mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, which generate R22(18) inversion dimers, and inter-connected by C(14) chains running along the c-axis direction, whereas in compound (II), the C-H⋯O hydrogen bonds generate R43(37) ring motifs. In the crystals of both compounds, C-H⋯O hydrogen-bonded sheets are formed lying parallel to (10-1). In addition, C-H⋯π and offset π-π inter-actions [inter-centroid distance = 3.7158 (14) Å in (I) and 3.9040 (15) Å in (II)] are also present in the crystals of both compounds.

Mechanistic Chemistry of Extraordinary Capacity of Salvianolic Acid B on Oxidatively‐damaged Mesenchymal Stem Cells

As the main bioactive component of Chinese herbal medicine Danshen, salvianolic acid B (Sal B, or lithospermic acid B) was observed to maintain the viability of mesenchymal stem cells (MSCs) treated by Fenton's reagent in the study. Interestingly, at a higher concentration, Sal B could even increase the viability rate to 175.1%. In mechanistic analysis experiments, Sal B was found to resist DNA destruction by •OH radical, scavenge various radicals in vitro, reduce Cu2+ → Cu+, chelate Fe2+ to yield an absorption maximum at 710 nm. Based on these results, we concluded that, (1) Sal B can not only protect MSCs against •OH‐induced damages, but also promote their proliferation. This extraordinary capacity makes Sal B an ideal candidate in MSCs transplantation especially when MSCs are polluted by iron‐overload or other oxidative stress factors and, can partly be responsible for the versatile properties of Sal B in pharmacology. The possible mechanisms of its protective effect are hypothesized to include Fe2+ chelating, and direct radical scavenging which is involved in electron transfer (ET) or hydrogen atom transfer (HAT) from the catechol moieties. Its proliferation‐promoting effect is presumed to be from its ester group, carboxylic group, or benzofuran ring.

SYNTHESIS AND X-RAY STRUCTURAL CHARACTERIZATION OF 1-(5-BROMOBENZOFURAN-2-YL)-2-MESITYLETHANONEOXIME AND 1-(5-BROMOBENZOFURAN-2-YL)-2-MESITYLETHANONE-O-(2- PHENYLACETYL)OXIME

The selected molecules of benzofuran derivatives were synthesized and their structures were studied using the X-ray crystallography and spectroscopic methods. The 1-(5-bromobenzofurane-2-yl)-2-mesitylethanoneoxime (I) , C19H18BrNO2, and 1-(5-bromobenzofuran-2-yl)-2-mesitylethanone- O -(2-phenylacetyl) oxime (II) , C27H24BrNO3, crystallize in the monoclinic crystal system in space group P21/c with Z = 4 and in the triclinic system in space group P-1 with Z=2, respectively. The both compounds adopt Z conformation. The compound (I) consists of a dimeric arrangement of molecules around an inversion centre formed via a O-H…N intermolecular hydrogen bond linking the molecules – Along the a axis. This centrosymmetric hydrogen-bonded dimers are formed with an R 2/2 (6) ring motif. The compound (II) forms one dimensional infinite chain via C–H···O hydrogen bond along the a axis. Moreover, in the crystal structures of (I), (II) weak C-H..O, C-H…π and π…π interactions serve to organize formation of a two dimensional network. Moreover a short N1-N1 intermolecular contact [2.89 A] is observed between inversion-related chains in the crystal structure of (I) . The two compounds have essentialy similar bond lengths and angles. The prominent discrepancy is observed for the fragment attaching benzofuran ring with mesityl group. Benzofuran groups and other ring groups are almost planar in the crystal structures of (I) and (II) .

Abstract 2914: Biphenylene and bipyridine connected benzofuran compounds as novel regulators of kRAS transcription

Abstract Pancreatic cancer is the fourth most deadly cancer with 5 year survival rate of ∼6%. One of the major attributes of pancreatic cancer is kRAS mutations. kRAS is a proto-oncogene with intrinsic GTPase activity, and is responsible for cell proliferation, division, and apoptosis. kRAS mutations are observed in >95% of pancreatic adenocarcinoma and in 30% all human tumors. When mutated it leads to continuous activity and uncontrolled proliferation which results in increased tumorigenicity and poor prognosis. Downregulating kRAS expression has shown to halt proliferation and leads to cellular death in pancreatic cancer models, but to date no small molecule capable of such transcriptional silencing has been described. A novel series of molecules with either biphenylene or bipyridine spacer connecting the terminal benzofuran ring was synthesized using solution phase chemistry. Tertiary amine side chains were incorporated to the C2-position of the benzofuran ring to improve the DNA binding affinity of these compounds. The synthesized compounds were purified using a “catch and release” method employing the sulfonic acid based resins. The eleven novel compounds were screened in parallel for their ability to stabilize G-quadruplex structures in the kRAS promoter, and to downregulate kRAS promoter activity. Two of the compounds increased the thermal profile of non-canonical DNA formations in the promoter region by >5 °C; however, on the whole these compounds did not seem to function as G-quadruplex-stabilizing agents. Eight compounds significantly decreased luciferase expression under the explicit control of the kRAS promoter by up to 75%, by compound BF 4.3, through an as-yet unknown mechanism of action. The compound series was examined for the inhibition of cellular viability in two mutant kRAS pancreatic cancer cell lines - Panc-1 and MIA PaCa-2; in both cell lines the compounds containing the bipyridine spacer had greater cytotoxic effects with IC50's of ∼30 μM, consistently. qPCR is being used to confirm the decrease in promoter activity in native cellular conditions. These agents are intriguing in both their novel scaffold and their unexpected activity decreasing kRAS expression in a mechanism unrelated to higher order DNA structures. Ultimately, down regulation of kRAS transcription will provide a novel therapeutic approach for pancreatic cancer and improve the prognosis of this highly lethal disease. Citation Format: Harshul Batra, Mohammad K. Islam, David E. Thurston, Khondaker M. Rahman, Tracy A. Brooks. Biphenylene and bipyridine connected benzofuran compounds as novel regulators of kRAS transcription. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2914.

2-(4,6-Dimethyl-1-benzofuran-3-yl)acetic acid

In the title compound, C12H12O3, the dihedral angle between the planes of the carboxylic acid group and the benzofuran ring system (r.m.s. deviation = 0.012 Å) is 76.53 (10)°. In the crystal, carboxylic acid inversion dimers linked by pairs of O—H...O hydrogen bonds generateR22(8) loops. C—H...O interactions link the dimers into (101) sheets.

Studies directed toward synthesis of taepeenin D: construction of the C4 stereogenic center and the CD benzofuran rings

Taepeenin D is a meroterpenoid isolated from roots and stems of Caesalpinia crista, showing inhibitory activity of Hedgehog signaling pathway. Herein we report selective and short-step construction of two fragments of taepeenin D. First, we demonstrated alkoxy radical-mediated selective functionalization at C19 methyl group for construction of the C4 quaternary carbon stereogenic center. Second, the CD benzofuran rings were constructed in 6 short steps from decalone. The synthesis described herein is not only applicable to total synthesis, but also used for study of the structure–activity relationships of taepeenin D.