Synthesis and Absolute Configuration of (−)-3-Butyl-7-hydroxyphthalide, a Cytotoxic Metabolite ofPenicillium vulpinum*

Both the enantiomers as well as the racemate of 3-butyl-7-hydroxyphthalide (1) were synthesized, and the absolute configuration of the naturally occurring (-)-1 (a weakly cytotoxic metabolite of Penicillium vulpinum) was identified as S.

Synthesis and Antioxidative Activity of 3′,4′,6,7-Tetrahydroxyaurone, a Metabolite ofBidens frondosa

3',4',6,7-Tetrahydroxyaurone (1a), an aurone isolated from Bidens frondosa, and five analogues (1b-1f) were synthesized from pyrogallol in three steps. The antioxidative activity of 1a-1f was determined by the superoxide free radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging methods.

Remodeling natural products: chemistry and serine hydrolase activity of a rocaglate-derived β-lactone

Flavaglines are a class of natural products with potent insecticidal and anticancer activities. β-Lactones are a privileged structural motif found in both therapeutic agents and chemical probes. Herein, we report the synthesis, unexpected light-driven di-epimerization, and activity-based protein profiling of a novel rocaglate-derived β-lactone. In addition to in vitro inhibition of the serine hydrolases ABHD10 and ACOT1/2, the most potent β-lactone enantiomer was also found to inhibit these enzymes, as well as the serine peptidases CTSA and SCPEP1, in PC3 cells.

Semisynthesis and insecticidal activity of some fraxinellone derivatives modified in the B ring

A series of novel fraxinellone derivatives modified at the C-1 or C-8 position in the B ring were prepared as insecticidal agents against the pre-third-instar larvae of oriental armyworm, Mythimna separata Walker at 1 mg/mL. Five key steric configurations of compounds 2, 3, and 8f,g,j were further determined by single-crystal X-ray diffraction. It was found that the kinds and the amount of the reduction products of fraxinellone were related to the molar ratio between the reduction agent Red-Al and the substrate fraxinellone. Among all of the derivatives, compounds 2 and 8i,j,o displayed more promising insecticidal activity than their precursors fraxinellone and toosendanin. The preliminary structure-activity relationships revealed that the lactone (B-ring) of fraxinellone contributed to the observed insecticidal activity; the double bond at the C-2 position of fraxinellone was not necessary for the insecticidal activity; conversion of the oxygen atom of carbonyl group on the lactone of fraxinellone to a sulfur one does not improve the insecticidal activity; introduction of electron-withdrawing groups on the phenyl ring of 8f, to the benzoyloxy series, could result in more potent compounds.

One-pot synthesis, FT-IR and density functional method (DFT) studies on N-benzyl-N-ethyl-N-[5-nitro-2-(1,1,3,3-Tetramethylbutylamino)-1-benzofuran-3-yl]amine

N-benzyl-N-ethyl-N-[5-nitro-2-(1,1,3,3-Tetramethylbutylamino))-1-benzofuran-3-yl]amine, 7, was synthesized and characterized by elemental analysis, FT-IR, (1)H and (13)C NMR spectra. The geometrical structures, vibrational frequencies, and molecular electrostatic potential (MEP) of 7 in the ground state were calculated by using the DFT/B3LYP method with 6-31 G(d) basis set. The optimized structure was compared with analogous compound. The IR spectrum of 7 was interpreted in terms of potential energy distribution (PED) analysis. Comparison of the experimental vibrational spectra of 7 with the theoretical data indicated good agreement.

Rhodium-catalyzed tandem annulation and (5 + 1) cycloaddition: 3-hydroxy-1,4-enyne as the 5-carbon component

A Rh-catalyzed tandem annulation and (5 + 1) cycloaddition was realized. 3-Hydroxy-1,4-enyne served as the new 5-carbon component for the (5 + 1) cycloaddition. Substituted carbazoles, dibenzofurans, and tricyclic compounds containing a cyclohexadienone moiety could be prepared efficiently. The identification of a byproduct suggests that metal carbene and ketene intermediates may be involved in the (5 + 1) cycloaddition.

Synthesis and biological evaluation of benzofuroxan derivatives as fungicides against phytopathogenic fungi

Forty-four benzofuroxan derivatives were designed and prepared as antifungal agents. Their structures were characterized by (1)H NMR, (13)C NMR, and HRMS. Their antifungal activities were tested in vitro with four important phytopathogenic fungi, namely, Rhizoctonia solani , Sclerotinia sclerotiorum , Fusarium graminearum and Phytophthora capsici , using the mycelium growth inhibition method. Compound A5 displayed the maximum antifungal activity against F. graminearum (IC50 = 1.1 μg/mL, which is about 2-fold higher than that of the well-known positive control carbendazim (IC50 = 0.5 μg/mL). A14 exhibited high antifungal effect against both S. sclerotiorum and F. graminearum Sehw., with IC50 values of 2.52 and 3.42 μg/mL, respectively. Among 14 benzofuroxan derivatives with substitutions at the R(2) and R(3) positions of the phenyl ring (B series), 7 compounds displayed strong growth inhibition against R. solani (IC50 ≤ 3.0 μg/mL). Analysis of the structure-activity relationship data of these compounds revealed that (1) introduction of an electron-donating amino group to the R(2) position of the phenyl ring favors antifungal activity against R. solani and (2) the presence of a nitro group at the R(4) position and substituent variation at the R(1) position of the phenyl ring can result in good antifungal candidates against F. graminearum Sehw. Overall, the benzofuroxan was discovered as a novel scaffold for the development of fungicides. Significantly, A14 was demonstrated to successfully suppress disease development in S. sclerotiorum infected cole in vivo.

A recyclable palladium-catalyzed synthesis of 2-methylene-2,3-dihydrobenzofuran-3-ols by cycloisomerization of 2-(1-hydroxyprop-2-ynyl)phenols in ionic liquids

A recyclable palladium-catalyzed synthesis of 2-methylene-2,3-dihydrobenzofuran-3-ols 2 by heterocyclization of 2-(1-hydroxyprop-2-ynyl)phenols 1 in an ionic liquid medium (BmimBF4) is presented. The process takes place under relatively mild conditions (100 °C, 5 h) in the presence of catalytic amounts (2 mol %) of PdI2 in conjunction with KI (5 equiv with respect to PdI2) and an organic base, such as morpholine (1 equiv with respect to 1), to give 2 in high yields (70%-86%). The PdI2-KI catalytic system could be recycled up to six times without appreciable loss of activity. Moreover, products 2 could be easily converted in a one-pot fashion into 2-hydroxymethylbenzofurans 3 (52%-71%, based on 1) and 2-methoxymethylbenzofurans 4 (52%-80%, based on 1) by acid-catalyzed allylic isomerization or allylic nucleophilic substitution.

Effects of stereoisomerism on the crystallization behavior and optoelectrical properties of conjugated molecules

Three stereoisomers of DPP(TBFu)2 are separated and identified to investigate the effects of stereoisomerism on crystal structures and the optoelectrical properties. The crystal structures and FET mobility are sensitive to stereoisomers, in which the mesomer possesses the highest carrier mobility and the greatest crystallization tendency to dominate the crystallization in spin-cast films of the as-synthesized stereoisomeric mixture.

Synthesis of new benzofuran-1,3-thiazolidin-4-one derivatives from natural sources and study of their antioxidant activity

Synthesis of benzofuran-1,3-thiazolidinone derivatives is described herein. These compounds were prepared via a concise and short route by condensation reaction of khellinone with aromatic/aliphatic amines followed by cyclization using thioglycolic acid. The newly synthesized compounds were characterized using the well known spectroscopic tools (IR, 1H NMR, and mass spectroscopy), as well as microanalysis. In frames of biological screening of the compounds, antioxidant activity was assessed in vitro.

Total synthesis of bisbibenzyl dibenzofuran asterelin A via intramolecular oxidative coupling

Total synthesis of asterelin A was accomplished by applying intramolecular Suzuki-Miyaura and oxidative couplings to the formation of an 18-membered macrocyclic ring and a dibenzofuran, respectively.

Synthetic analogues of the natural compound cryphonectric acid interfere with photosynthetic machinery through two different mechanisms

A series of isobenzofuran-1(3H)-ones (phthalides), analogues of the naturally occurring phytotoxin cryphonectric acid, were designed, synthesized, and fully characterized by NMR, IR, and MS analyses. Their synthesis was achieved via condensation, aromatization, and acetylation reactions. The measurement of the electron transport chain in spinach chloroplasts showed that several derivatives are capable of interfering with the photosynthetic apparatus. Few of them were found to inhibit the basal rate, but a significant inhibition was brought about only at concentrations exceeding 50 μM. Some other analogues acted as uncouplers or energy transfer inhibitors, with a remarkably higher effectiveness. Isobenzofuranone addition to the culture medium inhibited the growth of the cyanobacterium Synechococcus elongatus , with patterns consistent with the effects measured in vitro upon isolated chloroplasts. The most active derivatives, being able to completely suppress algal growth at 20 μM, may represent structures to be exploited for the design of new active ingredients for weed control.

A mechanistic and kinetic study on the formation of PBDD/Fs from PBDEs

This study presents a detailed mechanistic and kinetic investigation that explains the experimentally observed high yields of formation of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) from the polybrominated diphenyl ethers (PBDEs), commonly deployed in brominated flame retardants (BFRs). Theoretical calculations involved the accurate meta hybrid functional of M05-2X. The previously suggested pathways of debromination and generation of bromophenols/bromophenoxys/bromobenzenes were found to be unimportant corridors for the formation of PBDD/Fs. A loss of an ortho Br or H atom from PBDEs, followed by a ring-closure reaction, is the most accessible pathway for the production of PBDFs via modest reaction barriers. The initially formed peroxy-type adduct (RO₂) is found to evolve in a complex, nevertheless very exoergic, mechanism to produce PBDDs. Results indicate that, degree and pattern of bromination, in the vicinity of the ether oxygen bridge, has a minor influence on governing mechanisms and that even fully brominated isomers of BFRs are capable of forming PBDD/Fs. We thoroughly discuss bimolecular reactions of PBDEs with Br and H, as well as the Br-displacement reaction by triplet oxygen. The rate of the Br-displacement reaction significantly exceeds that of the unimolecular inititiation reactions due to loss of ortho Br or H. Results presented herein address conclusively the intriguing question of how PBDEs form PBDD/Fs, a matter that has been in the center of much debate among environmental chemists.

Benzofuran-, benzothiophene-, indazole- and benzisoxazole-quinones: excellent substrates for NAD(P)H:quinone oxidoreductase 1

A series of heterocyclic quinones based on benzofuran, benzothiophene, indazole and benzisoxazole has been synthesized, and evaluated for their ability to function as substrates for recombinant human NAD(P)H:quinone oxidoreductase (NQO1), a two-electron reductase upregulated in tumor cells. Overall, the quinones are excellent substrates for NQO1, approaching the reduction rates observed for menadione.

Studies on an (S)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptor antagonist IKM-159: asymmetric synthesis, neuroactivity, and structural characterization

IKM-159 was developed and identified as a member of a new class of heterotricyclic glutamate analogues that act as AMPA receptor-selective antagonists. However, it was not known which enantiomer of IKM-159 was responsible for its pharmacological activities. Here, we report in vivo and in vitro neuronal activities of both enantiomers of IKM-159 prepared by enantioselective asymmetric synthesis. By employment of (R)-2-amino-2-(4-methoxyphenyl)ethanol as a chiral auxiliary, (2R)-IKM-159 and the (2S)-counterpart were successfully synthesized in 0.70% and 1.5% yields, respectively, over a total of 18 steps. Both behavioral and electrophysiological assays showed that the biological activity observed for the racemic mixture was reproduced only with (2R)-IKM-159, whereas the (2S)-counterpart was inactive in both assays. Racemic IKM-159 was crystallized with the ligand-binding domain of GluA2, and the structure revealed a complex containing (2R)-IKM-159 at the glutamate binding site. (2R)-IKM-159 locks the GluA2 in an open form, consistent with a pharmacological action as competitive antagonist of AMPA receptors.

Synthesis, crystal structure and two-photon excited fluorescence properties of three aurone derivatives

Three aurone derivatives, Z-2-[(4-N,N-dimethylaminophenyl)methylene] benzofuran-3-one (1), Z-2-[(N-ethylcarbazol-3-yl)methylene]benzofuran-3-one (2) and Z-2-[(pyren-1-yl)methylene]benzofuran-3-one (3) have been synthesized by the cyclization of 2'-hydroxychalcones. Their crystal structure, single- and two-photon related absorption and fluorescence properties have been examined. Pumped by 860 nm laser pulses in femtosecond regime, the compounds exhibit strong yellow-green two-photon excited fluorescence at 539 nm (1), 505 nm (2) and 524 nm (3) in THF with two-photon absorption (TPA) cross-section being 1536GM (1), 608GM (2) and 236GM (3).

Synthesis of a potent antimalarial agent through natural products conjugation

Au naturel! (+)-Usnic acid (green) is a weak antimalarial agent, however, in conjugation with known antimalarial scaffolds and drugs, such as dihydroartemisinin (blue), potent activity against the blood-stage parasite can be seen both in vitro and in vivo. The compound shown exhibits an IC(50) value of 1.4 nM against Plasmodium falciparum in vitro and proved nearly as efficacious as artesunate in a mouse model of infection.

Pd(II)-catalyzed enantioselective C-H activation/C-O bond formation: synthesis of chiral benzofuranones

Pd(II)-catalyzed enantioselective C-H activation of phenylacetic acids followed by an intramolecular C-O bond formation afforded chiral benzofuranones. This reaction provides the first example of enantioselecctive C-H functionalizations through Pd(II)/Pd(IV) redox catalysis.

Synthesis, anticonvulsant and neurotoxicity evaluation of some newer N-(2-benzoylbenzofuran-3-yl)-3-(substituted)-propanamide analogs

A series of 12, N-(2-benzoylbenzofuran-3-yl)-3-(substituted)-propanamide analogs was designed and synthesized to meet the pharmacophore requirement essential for anticonvulsant activity. All the compounds were characterized by IR, (1)H NMR and mass spectral data followed by their anticonvulsant evaluation according to the Antiepileptic Drug Development Program (ADD) protocol. The present study has proved the hypothesis concerning the pharmacophore model with essential binding sites. N-(2-benzoylbenzofuran-3-yl)-3-(4-(2-fluorophenyl)piperazin-1-yl) propanamide, 6h was found to be the most active compound in both maximal electroshock seizure (MES) and subcutaneous metrazol (scMET) seizure test at 30 and100 mg/kg respectively at 0.5 and 4.0 h.

σ-1 receptor at the mitochondrial-associated endoplasmic reticulum membrane is responsible for mitochondrial metabolic regulation

The mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) is a small section of the outer mitochondrial membrane tethered to the ER by lipid and protein filaments. One such MAM protein is the σ-1 receptor, which contributes to multiple signaling pathways. We found that short interfering RNA-mediated knockdown of σ-1 reduced pregnenolone synthesis by 95% without affecting expression of the inner mitochondrial membrane resident enzyme, 3-β-hydroxysteroid dehydrogenase 2. To explore the underlying mechanism of this effect, we generated a series of σ-receptor ligands: 5,6-dimethoxy-3-methyl-N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamide (KSCM-1), 3-methyl-N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamide (KSCM-5), and 6-methoxy-3-methyl-N-phenyl-N-(3-(piperidin-1-yl) propyl)benzofuran-2-carboxamide (KSCM-11) specifically bound to σ-1 in the nanomolar range, whereas KSCM-5 and KSCM-11 also bound to σ-2. Treatment of cells with the KSCM ligands led to decreased cell viability, with KSCM-5 having the most potent effect followed by KSCM-11. KSCM-1 increased σ-1 expression by 4-fold and progesterone synthesis, whereas the other compounds decreased progesterone synthesis. These differences probably are caused by ligand molecular structure. For example, KSCM-1 has two methoxy substituents at C-5 and C-6 of the benzofuran ring, whereas KSCM-11 has one at C-6. KSCM ligands or σ-1 knockdown did not alter the expression of ER resident enzymes that synthesize steroids. However, coimmunoprecipitation of the σ-1 receptor pulled down voltage-dependent anion channel 2 (VDAC2), whose expression was enhanced by KSCM-1. VDAC2 plays a key role in cholesterol transport into the mitochondria, suggesting that the σ-1 receptor at the MAM coordinates with steroidogenic acute regulatory protein for cholesterol trafficking into the mitochondria for metabolic regulation.

Synthesis of N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamides as new selective ligands for sigma receptors

Novel benzofuran-2-carboxamide ligands, which are selective for sigma receptors, have been synthesized via a microwave-assisted Perkin rearrangement reaction and a modified Finkelstein halogen-exchange used to facilitate N-alkylation. The ligands synthesized are the 3-methyl-N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamides (KSCM-1, KSCM-5 and KSCM-11). The benzofuran-2-carboxamide structure was N-arylated and N-alkylated to include both N-phenyl and N-(3-(piperidin-1-yl)propyl substituents, respectively. These new carboxamides exhibit high affinity at the sigma-1 receptor with K(i) values ranging from 7.8 to 34nM. Ligand KSCM-1 with two methoxy substituents at C-5 and C-6 of the benzofuran ring, and K(i)=27.5nM at sigma-1 was found to be more selective for sigma-1 over sigma-2.

Synthesis and herbicidal potential of substituted aurones

BACKGROUND

With the objective of exploring the herbicidal activity of substituted aurones, a series of 4,6-disubstituted and 4,5,6-trisubstituted aurones were synthesised, and their herbicidal activities against Brassica campestris L. and Echinochloa crusgalli (L.) Beauv. were evaluated in laboratory bioassays. Effects of some of the compounds were evaluated on seed germination. The most active compounds in the laboratory were evaluated in the greenhouse.

RESULTS

The compounds were characterised by (1)H NMR, (13)C NMR and HRMS; some of them were further identified by IR. A (Z)-configuration was assigned to the aurones, based on spectroscopic and crystallographic data. Bioassay results of root growth showed that the aurones had a moderate herbicidal activity against the dicotyledonous plant Brassica campestris. (Z)-2-Phenylmethylene-4,6-dimethoxy-3(2H)-benzofuranone(6o) was the most active compound, with 81.3 and 88.5% inhibition at 10 and 100 µg ml(-1) respectively, equal to the activity of mesotrione. Some of the aurones possessed some inhibition of germination on several plant species. For glasshouse tests, the substituted aurones had lower herbicidal activity than metolachlor and mesotrione.

CONCLUSION

It is possible that aurone derivatives, which possess structures different from those of the commercial herbicides, may become novel lead compounds for the development of herbicides against dicotyledonous weeds with further structure modification.

Synthesis and characterization of selected methyl 5-methoxy-2-methyl-1-benzofuran-3-carboxylate derivatives with potential antimicrobial activity

Halogen and aminoalkyl derivatives of methyl 5-methoxy-2-methyl-1-benzofuran-3-carboxylate were prepared using 5-hydroxy-2-methyl-3-benzofuranocarboxylic acid as starting material. (1)H-NMR spectra were obtained for all of the synthesized structures, and for compounds 1 and 2 X-ray crystal structures were obtained too. All derivatives were tested for antimicrobial activity against a selection of Gram-positive cocci, Gram-negative rods and yeasts.

Design and synthesis of inhibitors of Plasmodium falciparum N-myristoyltransferase, a promising target for antimalarial drug discovery

Design of inhibitors for N-myristoyltransferase (NMT), an enzyme responsible for protein trafficking in Plasmodium falciparum , the most lethal species of parasites that cause malaria, is described. Chemistry-driven optimization of compound 1 from a focused NMT inhibitor library led to the identification of two early lead compounds 4 and 25, which showed good enzyme and cellular potency and excellent selectivity over human NMT. These molecules provide a valuable starting point for further development.

Elucidating the formation pathway of the off-flavor compound 6-propylbenzofuran-7-ol

In a previous work, we identified 6-propylbenzofuran-7-ol as an off-flavor compound formed from ascorbic acid and (E)-hex-2-enal in a test apple beverage. In this study, we elucidate the pathway by which 6-propylbenzofuran-7-ol formed. Isotope labeling studies revealed that the propyl group of 6-propylbenzofuran-7-ol derives from (E)-hex-2-enal and that 6-propylbenzofuran-7-ol contains carbons 2-6 of ascorbic acid. Two compounds, namely, 2,3-dihydro-6-propylbenzofuran-3,7-diol and 3-(2-furoyl)hexanal, were identified as byproducts of a model reaction of ascorbic acid and (E)-hex-2-enal. Each of these compounds was dissolved in an aqueous solution of citric acid and stored at 60 °C for 1 week. After storage, 6-propylbenzofuran-7-ol was detected from a solution of 2,3-dihydro-6-propylbenzofuran-3,7-diol, but not from 3-(2-furoyl)hexanal. 6-Propylbenzofuran-7-ol was formed by isolating tricyclic hemiacetal lactone derived from the Michael addition of ascorbic acid to (E)-hex-2-enal, mixing the tricyclic hemiacetal lactone with the aqueous solution of citric acid, and applying heat. This confirmed that 6-propylbenzofuran-7-ol was formed via the Michael adduct.