A novel sustainable strategy for the synthesis of phenols by magnetic CuFe2O4-catalyzed oxidative hydroxylation of arylboronic acids under mild conditions in water

Secondary metabolites and transcriptomic analysis of novel pulcherrimin producer Metschnikowia persimmonesis KIOM G15050: A potent and safe food biocontrol agent

Metschnikowia persimmonesis, a novel endophytic yeast strain isolated from Diospyros kaki calyx, possesses strong antimicrobial activity. We investigated its potential use as an environmentally safe food biocontrol agent through genomics, transcriptomics, and metabolomics. Secondary metabolites were isolated from M. persimmonesis, followed by chemical structure elucidation, PUL gene cluster identification, and RNA sequencing. Pulcherrimin was isolated using 2 M NaOH, its structure was confirmed, and the yield was quantified. Biocontrol efficacy of M. persimmonesis on persimmon fruits and calyx was evaluated by assessing lesion diameter and disease incidence. Following compounds were isolated from M. persimmonesis co-culture with Botrytis cinerea and Fusarium oxysporum: fusaric acid, benzoic acid, benzeneacetic acid, 4-hydroxybenzeneacetic acid, 4-(-2-hydoxyethyl)-benzoic acid, cyclo (Leu-Leu), benzenemethanol, 4-hydroxy-benzaldehide, 2-hydroxy-4-methoxy-benzoic acid, 4-hydroxy-benzoic acid, lumichrome, heptadecanoic acid, and nonadecanoic acid. Exposing M. persimmonesis to different growth media conditions (with or without sugar) resulted in the isolation of five compounds: Tyrosol, Cyclo (Pro-Val), cyclo(L-Pro-L-Tyr), cyclo(Leu-Leu), and cyclo(l-tyrosilylicine). Differentially expressed gene analysis revealed 3264 genes that were significantly expressed (fold change ≥2 and p-value ≤0.05) during M. persimmonesis growth in different media, of which only 270 (8.27%) showed altered expression in all sample combinations with Luria-Bertani Agar as control. Minimal media with ferric ions and tween-80 triggered the most gene expression changes, with the highest levels of PUL gene expression and pulcherrimin yield (262.166 mg/L) among all media treatments. M. persimmonesis also produced a higher amount of pulcherrimin (209.733 mg/L) than Metschnikowia pulcherrima (152.8 mg/L). M. persimmonesis inhibited the growth of Fusarium oxysporum in persimmon fruit and calyx. Toxicity evaluation of M. persimmonesis extracts showed no harmful effects on the liver and mitochondria of zebrafish, and no potential risk of cardiotoxicity in hERG-HEK293 cell lines. Thus, M. persimmonesis can be commercialized as a potent and safe biocontrol agent for preserving food products.

Metal-Free Oxidative Formation of Aryl Esters by Catalytic Coupling of Acyl and Sulfonyl Chlorides with Arylboronic Acids

A practical and efficient synthesis of aryl esters was developed through metal-free oxidation. This reaction employs stable and readily available acyl or sulfonyl chlorides and arylboronic acids as the starting materials and proceeds under mild reaction conditions without additional precious metal catalysts. This new strategy exhibits broad substrate tolerance and operational simplicity and gives diverse aryl esters in moderate to high yields.

Linker-Assisted CdS-TiO2 Nanohybrids as Reusable Visible Light Photocatalysts for the Oxidative Hydroxylation of Arylboronic Acids

A variety of phenols have been obtained in aqueous media with moderate to excellent chemical yields (≤100%) by using arylboronic acids and esters as substrates, a robust CdS-TiO₂ nanohybrid as a heterogeneous photocatalyst, visible light irradiation (467 nm), and an O₂-saturated atmosphere. The nanohybrid was prepared through a linker-assisted methodology that uses mercapto alkanoic acids as the organic linkers. The nanohybrid showed improved photocatalytic activity in the hydroxylation of substituted arylboronic acids and phenyl boronic esters compared with that of pristine CdS quantum dots. The nanohybrid can be reused in up to five photocatalytic cycles with ∼90% of its outstanding activity preserved.

Surface Nanoarchitectonics of Boron Nitride Nanosheets for Highly Efficient and Sustainable ipso-Hydroxylation of Arylboronic Acids

One of the important industrial processes commonly employed in the pharmaceutical, explosive, and plastic manufacturing industries is ipso-hydroxylation of arylboronic acids. In this work, a straightforward, metal-free methodology for the synthesis of phenols from arylboronic acids has been demonstrated using hydroxyl functionalized boron nitride (BN-OH) nanosheets. The functionalized hydroxyl groups on the BN nanosheets act as the active sites for the hydroxylation reaction to take place. The detailed optimization of reaction parameters was done in order to attain high catalytic efficiency, and the reactions were conducted in water, which eliminates the use of toxic solvents. The as-synthesized catalysts exhibited excellent recyclability and reusability in addition to high product yields and good turnover numbers. The green metrics parameters were also evaluated for the model reaction to examine the sustainable nature of the developed protocol. The use of BN-OH catalysts for the ipso-hydroxylation reactions under base-free and metal-free conditions using environmentally benign solvents is utmost desired for industrial processes and can pave a way toward sustainable organic catalysis.

Autocatalytic aerobic ipso-hydroxylation of arylboronic acid with Hantzsch ester and Hantzsch pyridine

ipso-Hydroxylation of arylboronic acids with Hantzsch ester has been developed. The by-product Hantzsch pyridine was found to promote the reaction in the presence of oxygen under ambient conditions.

The graphite-catalyzed ipso-functionalization of arylboronic acids in an aqueous medium: metal-free access to phenols, anilines, nitroarenes, and haloarenes

An efficient, metal-free, and sustainable strategy has been described for the ipso-functionalization of phenylboronic acids using air as an oxidant in an aqueous medium. A range of carbon materials has been tested as carbocatalysts. To our surprise, graphite was found to be the best catalyst in terms of the turnover frequency. A broad range of valuable substituted aromatic compounds, i.e., phenols, anilines, nitroarenes, and haloarenes, has been prepared via the functionalization of the C-B bond into C-N, C-O, and many other C-X bonds. The vital role of the aromatic π-conjugation system of graphite in this protocol has been established and was observed via numerous analytic techniques. The heterogeneous nature of graphite facilitates the high recyclability of the carbocatalyst. This effective and easy system provides a multipurpose approach for the production of valuable substituted aromatic compounds without using any metals, ligands, bases, or harsh oxidants.

Sonochemically Synthesized Spin-Canted CuFe2O4 Nanoparticles for Heterogeneous Green Catalytic Click Chemistry

Heterogeneous green catalysis by using magnetically separable nanometal-oxide catalysts has become a subject of prime focus recently. PXRD (powder X-ray diffraction), FESEM (field emission scanning electron microscopy), and HRTEM (high-resolution tunneling electron microscopy) with IR and Raman spectroscopy are applied to analyze the structural and microstructural properties of nanosized (∼15.3 nm) CuFe₂O₄ synthesized by both sonochemical and mechanochemical processes. The sonochemical process provides a better uniformity of sizes of the nanoparticles (NPs). Rietveld refinement with the PXRD pattern reveals the inverse spinel-like architecture of CuFe₂O₄ NPs. The Raman spectra also indicate the phase purity of the synthesized material. The static magnetic measurements are performed at different magnetic fields and temperature ranges from 300 to 5 K, which confirms the existence of the ferrimagnetic phase mixed with some finer superparamagnetic (SPM) nanophases within the sample. Unsaturated magnetization is observed even at an applied 5 T magnetic field for the presence of spin-canting nature in the partially inverted copper ferrite phases at the surfaces of the nanoparticles. Now, these coupled magnetic CuFe₂O₄ NPs are used as a heterogeneous catalyst for three-component Huisgen 1,3-dipolar cycloaddition click reaction in aqueous media. By this catalyst system, we were able to couple alkyl halide, epoxide, or boronic acid with alkynes efficiently to furnish 1,4-disubstituted 1,2,3-triazoles in excellent yields within very short reaction time. The test for heterogeneity, reusability, and reproducibility of the catalyst has also been performed successfully without prominent decrease in yield up to the fifth cycle.

Trichloroacetonitrile as an efficient activating agent for the ipso-hydroxylation of arylboronic acids to phenolic compounds

An efficient and practical method for the ipso-hydroxylation of arylboronic acids was developed using TBHP and Cl₃CCN under base-free conditions with blue-LED irradiation.

A facile hydroxylation of arylboronic acids mediated by sodium ascorbate

A mild and selective method for the synthesis of phenols has been described.

Two new compounds from a marine-derived Streptomyces sp

Two new long-chain unsaturated compounds, (2E, 6E)-10-methoxy-3,7-dimethyl-10-oxodeca-2,6-dienoic acid (1) and (2E, 6E)-3,7,11-trimethyldodeca-2,6-dienedioic acid (2), together with seven known compounds were isolated from a marine-derived Streptomyces sp. Their structures were determined by spectroscopic methods, including 2D NMR techniques. Compounds 1 and 2 were investigated for their antibacterial activities.

Synthesis of triphenylamines via ligand-free selective ring-opening of benzoxazoles or benzothiazoles under superparamagnetic nanoparticle catalysis

Synthesis of triphenylamines via ligand-free selective ring-opening of benzoxazoles or benzothiazoles with aryl halides under CuFe₂O₄ superparamagnetic nanoparticle catalysis.

Allelochemicals from the Rhizosphere Soil of Cultivated Astragalus hoantchy

Astragalus hoantchy, a widely cultivated medicinal plant species in traditional Chinese and Mongolian medicine, has been often hampered by replant failure during cultivation, like many other herbs of the genus Astragalus. Root aqueous extracts of Astragalus herbs were reported to exhibit allelopathic activity against other plants and autotoxic activity on their own seedlings, but the allelochemicals released by Astragalus plants have not been specified so far. Ten compounds were isolated from the rhizosphere soil extract of cultivated A. hoantchy and elucidated by spectroscopic analysis. Compounds 1-6 observably showed allelopathic activity against Lactuca sativa seedlings and autotoxic activity against A. hoantchy seedlings. The isolated compounds were further confirmed and quantified by high-performance liquid chromatography (HPLC) in the rhizosphere soil, with a total concentration of 9.78 μg/g (dry weight). These results specify and verify the allelochemicals released by cultivated A. hoantchy into the soil environment, which may provide new insights into the allelopathic mechanisms of this medicinal plant and probably assist in clarifying the replant problems of Astragalus plants.

Copper(II)-mediated O-arylation of protected serines and threonines

An effective protocol toward the O-arylation of β-hydroxy-α-amino acid substrates serine and threonine has been developed via Chan-Lam cross-coupling. This Cu(II)-catalyzed transformation involves benign open-flask conditions that are well-tolerated with a variety of protected (Boc-, Cbz-, Tr-, and Fmoc-) serine and threonine derivatives and various potassium organotrifluoroborates and boronic acids.

Magnetic copper ferrite nanoparticles/TEMPO catalyzed selective oxidation of activated alcohols to aldehydes under ligand- and base-free conditions in water

A novel, effective and sustainable strategy for the synthesis of aldehydes under ligand and base free conditions has been developed using inexpensive, readily available, oxygen-stable and recyclable CuFe₂O₄ nanoparticles as the catalyst.