Lead Tetraacetate Research Articles

Synthetic studies on fusicoccin A: Enantioselective synthesis of the C-ring fragment

The enantioselective synthesis of the C-ring fragment of fusicoccin A is described. The TBS ether of hydroxyketone prepared by baker’s yeast reduction was converted to the α-ethylidene ketone by aldol condensation with propionaldehyde, followed by Michael reaction with divinylcopper reagent and conversion to enol triflate to afford a single diastereomer. X-ray crystallographic analysis of the crystalline derivative of the single diastereomer showed that the asymmetric carbon formed by the Michael reaction was consistent with the configuration of the C15 asymmetric carbon of fusicoccin A. The vinyl group of the enol triflate was converted to a hydroxymethyl group by selective dihydroxylation with a bulky ligand, oxidative cleavage of the resultant 1,2-diol with lead tetraacetate, and DIBAL-H reduction. The hydroxymethyl group was subsequently converted to TBS ether, followed by the hydrogenolysis of the benzyl group and Dess–Martin oxidation, accomplishing the enantioselective synthesis of the desired C-ring fragment of fusicoccin A.

Oxidative photochemical cyclisations to access spiroketals

The spiroketal moiety is an important substructure within many biological natural products. One method to access them is via the oxidative cyclisation of a pendant hydroxyl group on to a pre‐formed pyran. However applications of this methodology have been severely limited by requiring the use of toxic and powerful oxidants, such as lead (IV) tetraacetate or mercuric oxide. Herein we report a novel and high yielding photochemical route to prepare complex spiroketals using a photochemical oxidative approach with mild and non‐toxic reagents and demonstrate the methodology to the synthesis of a number of insect pheromones.

Identification of the Hub Genes Linked to Lead (IV)-Induced Spleen Toxicity Using the Rat Model.

Exposure to lead (Pb) has harmful effects on the organs of both humans and animals, particularly the spleen. However, the precise mechanisms through which Pb (IV) exposure leads to spleen toxicity remain unclear. Hence, this study aimed to identify the key genes and signaling pathways involved in spleen toxicity caused by Pb (IV) incubation. We obtained the dataset GSE59925 from the Gene Expression Omnibus, which included spleen samples treated with lead tetraacetate (PbAc4) as well as control samples on the 1st and 5th day. Through differential expression analysis, we identified 607 and 704 differentially expressed genes (DEGs) in the spleens on the 1st and 5th day following PbAc4 treatment, respectively, with 245 overlapping DEGs between the two time points. Gene ontology analysis revealed that the commonly shared DEGs were primarily involved in signal transduction, drug response, cell proliferation, adhesion, and migration. Pathway analysis indicated that the common DEGs were primarily associated with MAPK, TNF, cAMP, Hippo, and TGF-β signaling pathways. Furthermore, we identified the hub genes such as CXCL10, PARP1, APOE, and VDR contributing to PbAc4-induced spleen toxicity. This study enhances our understanding of the molecular mechanisms underlying Pb (IV) toxicity in the spleen.

Oxidative α-sulfonyloxylation of aryl ketones with sulfonic acids by lead tetraacetate

Oxidative α-sulfonyloxylation of aryl ketones with sulfonic acids by lead tetraacetate

6,7-Dihydroxy-5,8-dimethoxy-2H-chromen-2-one

This article presents a novel approach for synthesizing a new 5,8-dimethoxy derivative of esculetin via the selective cleavage of the methylene bridge in sabandin—naturally occurring and easily synthetically accessible methoxylated coumarin. A high selectivity is achieved by using acetoxylation of methylenedioxy group with lead tetraacetate. Natural coumarin sabandin as a starting compound was prepared in a few simple steps from 5-allyl-4,7-dimethoxybenzo[d][1,3]dioxole (apiol), which is readily available from parsley and dill seed extracts. The developed method enables an efficient and straightforward synthesis of a new derivative of esculetin with potential medicinal and therapeutic applications.

Dual functional lead tetraacetate oxidant in Spiro-OMeTAD toward efficient and stable perovskite solar cells

Spiro-OMeTAD represents the benchmark hole transport material (HTM) in the state-of-the-art perovskite solar cells (PSCs). However, restricted by the low conductivity of pristine spiro-OMeTAD, dopants and a long oxidation process are required to improve the conductivity and hole mobility. The long oxidation in air not only prolongs the device fabrication period, but also leads to the decomposition of perovskite layer. Even worse, dopants such as tBP and Li-TFSI will be severely affected and cause irreversible damage during the long oxidation process, which will greatly affect the device performances. In this regard, a strong oxidant lead tetraacetate (LTA) is introduced into spiro-OMeTAD to significantly accelerate the oxidation process. Excitingly, the Pb2+ ions generate as a result of the reduction of LTA could strongly coordinate with tBP, thus hindering the evaporation of tBP, as well as the agglomeration of Li-TFSI. As a result, the PSCs based on LTA-doped spiro-OMeTAD show a high photo-to-electric conversion efficiency of 22.08% with excellent long-term stability and thermal stability. Overall speaking, LTA is commercially available and low-cost, more importantly, the accelerate oxidation process as well as the effect to stabilize the dopants in spiro-OMeTAD, makes it potential as a p-dopant for highly efficient and stable PSCs.

Facile Conversion of Aryl Amines Having No α-Methylene to Aryl Nitriles.

Dimethyl carbonimidodithioates, 2 derived from various primary aryl amines (1) by reacting with carbon disulfide and methyl iodide in dimethyl formamide in the presence of concentrated sodium hydroxide, are converted to the diaziridine derivatives, 3 by reacting with hydrazine in ethanol. The diaziridines, 3 on oxidation with lead tetraacetate in refluxing xylene, extrudes nitrogen, and intramolecular stabilization, particularly 1,2-carbon migration, takes place to give the product, 5. The reaction may take place through the intermediates, diazirines, 4, which have not been isolated. This work provides a new approach for the conversion of aryl amines having no α-methylene to aryl nitriles.

Synthesis, characterization and biological evaluation of some 2-arylbenzoxazole acetic acid derivatives as potential anticancer agents

A series of 2-arylbenzoxazole compounds possessing a cytotoxic activity as potential anticancer agents has been synthesised. Oxidative coupling of benzaldehyde with o -aminophenol utilizing lead tetraacetate approach has been used to realize the synthesis of compounds 1 - 11 . The cytotoxicity of 1 - 11 have been screened against breast cancer cell line MCF-7 and human colon cancer cell line HCT-116 utilizing doxorubicin as reference drug. Among these compounds, 2-(3-benzyloxyphenyl)benzoxazole-5-acetic acid 5 and 2-(4-methoxyphenyl)benzoxazol-5-acetic acid 10 , are found to be promising cytotoxic compounds against MCF-7 cell line. In addition, this study shows that the presence of acetic acid group at position 5 of benzoxazole nucleus enhances the activity. Moreover, it is noticed that the presence of oxygen atom directly linked to the phenyl substituent improves activity. The results offer a new benzoxazole based template to design and develop novel antineoplastic agents.

Lead tetraacetate assisted formation of bis(acetoxy)acetic acid derivative from carvone

R-Carvone on heating with Pb(OAc)4 in benzene gives (2RS)-2-hydroxy-2-[(1S)-4-methyl-5-oxocyclohex-3-en-1-yl)]-prop-1-yl bis(acetoxy)acetate. Alkaline hydrolysis of this compound affords the corresponding diol which under acidic catalysis is transformed into bis-hydroxy ether and 1,4-dioxane derivatives.

Oxidative Functionalization of Trinor-18α-olean-17(22)-ene Derivatives. Annulation of the E-Ring by an Intramolecular Aldol Reaction.

cis-Dihydroxylation of trinor-18α-olean-17(22)-ene 2 with osmium tetroxide led to diol 9. Its cleavage with lead tetraacetate gave tetracyclic ketoaldehyde 10. By comparison, the ozonation of trinor-18α-olean-17(22)-ene 2 in the presence of p-toluenesulfonic acid gave the corresponding ketoacetal 12. Both products were subjected to an intramolecular aldol reaction under the acidic conditions and yielded unusual triterpenes bearing a bicyclo[4.3.1]decane fragment (22). Further manipulation of the protective groups afforded compounds useful in triterpene synthesis, especially in the preparation of potentially biologically active saponins based on a tetracyclic terpene core.

Lead Tetraacetate in Organic Synthesis

Lead Tetraacetate in Organic Synthesis

Bridged-Selective Intramolecular Diels-Alder Reactions in the Synthesis of Bicyclo[2.2.2]octanes.

Regioselectivity for intramolecular Diels-Alder (IMDA) reactions of 6-acetoxy-6-alkenylcyclohexa-2,4-dien-1-ones that were formed by oxidation of 2-alkenylphenols with lead tetraacetate in acetic acid were studied. Bridged regioselectivity was observed in the IMDA reactions of 6-acetoxy-6-alkenylcyclohexa-2,4-dien-1-ones having a dienophile part which could conjugate with an aromatic group. Bridged seven- and eight-membered rings and bicyclo[2.2.2]octane skeletons were constructed by the present IMDA reactions. Density functional theory (DFT) calculations suggested that conjugation of the dienophile with neighboring aromatic groups lowered the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap and preceded bridged [4 + 2] adducts.

Correlation Between the Electrochemical Activity and the Crystallite Size of PbO2: A Comparative Study Between the Chemical and the Electrochemical Routes

Lead dioxide was prepared by chemical and electrochemical routes. The chemical samples were obtained by dissolving lead tetra-acetate in distilled water at room temperature. The electrochemical samples were obtained by oxidizing cured plates in sulfuric acid containing different concentrations of surfactant. The discharge of the different samples in sulfuric acid showed that the capacity of the chemical electrodes is independent of the crystallite size. In contrast the capacity of the electrochemical powders decreases with the increase of the crystallite size. Thermal analyses of the different samples were investigated to show the difference between the two methods.

Concerning the Stereoselectivity of the Oxidative Dimerization of 3-Alkyl-2-Hydroxy-1,4-Naphthoquinones in the Synthesis of Hybocarpone

Reinvestigation of 2-hydroxy-3-alkylnaphthoquinones oxidative dimerization was carried out. On the example of dihydrolapachol it is shown that the oxidative dimerization of 2-hydroxy-3-alkylnaphthoquinones upon treatment with lead tetraacetate or cerium ammonium nitrate in aprotic media leads to the formation of diastereomeric 5a S*,6a S*,12a S*,12b S*- and 5a S*,6a R*,12a R*,12b S*-dihydrobinaphthofurantetraones (1:1). This result is significantly different from the previous one.

A Facile, Efficient and Convenient One Pot Synthesis of Benzoxazoles from 1,2-diols and 2-aminophenols with Pb(OAc)4 Reagent

Background: In this work, a series of benzoxazole derivatives has been synthesized using 1,2-diols and 2-aminophenols in the presence of lead tetraacetate. This one pot cyclocondensation involves the breaking of a C-C bond and formation of C-O and C-N bonds in a single synthetic operation. Methods: The synthesis of benzoxazole derivatives is developed through the reaction of 1,2-diols and 2-aminophenols in the presence of lead tetraacetate in ethanol under reflux conditions. Results: A series of benzoxazole derivatives was synthesized in good yields (82-96%) under reflux for 2-3.5 hours in ethanol solvent. The structural assignments of these compounds were made on the basis of elemental analysis and spectroscopic data. Conclusion: This domino reaction implies oxidation, condensation, cyclization and dehydrogenation. This procedure is an alternative to the existing procedures for the synthesis of these compounds. Keywords: Benzoxazole, oxazole, lead tetraacetate, one pot synthesis, 1, 2-diols, ethanol solvent.

Antimicrobial photodynamic inactivation is potentiated by the addition of selenocyanate: Possible involvement of selenocyanogen?

We previously showed that antimicrobial photodynamic inactivation (aPDI) of Gram-positive and Gram-negative bacteria mediated by the phenothiazinium dye, methylene blue (MB), was potentiated by the addition of potassium thiocyanate (10 mM). The mechanism was suggested to involve a singlet oxygen-mediated reaction with SCN to form sulfite and cyanide and then to produce sulfur trioxide radical anion. We now report that potassium selenocyanate (concentrations up to 100 mM) can also potentiate (up to 6 logs of killing) aPDI mediated by a number of different photosensitizers (PS): MB, rose bengal and 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin dihydrochloride (as low as 200 nM). When a mixture of selenocyanate with these PS in solution was illuminated and then bacteria were added after the light, there was up to 6 logs of killing (Gram-negative > Gram-positive) but the antibacterial species decayed rapidly (by 20 minutes). Our hypothesis to explain this antibacterial activity is the formation of selenocyanogen (SeCN)2 by reaction with singlet oxygen (1 O2 ) as shown by quenching of 1 O2 by SeCN and increased photoconsumption of oxygen. The fact that lead tetraacetate reacted with SeCN (literature preparation of (SeCN)2 ) also produced a short-lived antibacterial species supports this hypothesis.

On the electrochemical activity of β-lead dioxide in sulfuric acid solution: a comparative study between the chemical and electrochemical routes

β-Lead dioxide is prepared by chemical and electrochemical routes. The chemical sample is obtained by dissolving lead tetra-acetate in distilled water at room temperature. The electrochemical sample is prepared by oxidizing cured plates in sulfuric acid with 1.05 g cm−3 specific gravity. The two powders are indexed as β-PbO2. The sample prepared by chemical route presents smaller crystallite size. When cycling the two powders up to 100 cycles between 0.5 and 1.5 V versus Hg/Hg2SO4 reference electrode, the electrochemical sample presents higher values of anodic and cathodic peak current densities and higher discharge capacity. Thermal analysis and electrochemical techniques are used to explain this difference in activity between the two samples.

Biginelli Reaction of Vicinal Diols: A New Route for One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-One Derivatives

Background: 3,4-Dihydropyrimidin-2(1H)-one derivatives are an important class of nitrogen heterocycles. These compounds present a wide range of biological activities viz antibacterial, antifungal, and antidiabetic. Although many synthetic methods are available in the literature for the synthesis of these molecules, many of these methods have their own limitations such as use of excess of expensive catalyst and poor yields. Methods: The synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives is developed through the reaction of 1,2-diols, ethyl acetoacetate and urea in the presence of lead tetraacetate in dry ethanol under reflux conditions. Results: A series of 3,4-dihydropyrimidin-2(1H)-one derivatives were synthesized in good yields (82-95%) under reflux for 2-3.5 hours in ethanol solvent. The structural assignments of these compounds were made on the basis of elemental analysis and spectroscopic data. Conclusion: This protocol is an alternative to existing procedure for the synthesis of Biginelli compounds. The present methodology reduces the number of steps in total synthesis. Keywords: Biginelli reaction, pyrimidine, 3, 4-dihydropyrimidin-2(1H)-one, lead tetraacetate, multicomponent reaction, 1, 2- diols.

One-Pot Synthesis of 2,4,5-Triphenyl Imidazoles from 1,2-Diols as Key Reagents

A simple one-pot procedure for the preparation of 2,4,5-triphenyl imidazole derivatives is presented. The procedure involves the lead tetraacetate oxidation of 1,2-diols to give aldehydes in situ, which then undergo a three-component reaction with benzil and ammonium acetate to yield the imidazole derivatives.

Synthesis 5-(pyrazolin-3-ylmethylidene)-2-thiohydantoins and 2-alkylsulfanyl-5-(pyrazolin-3-ylmethylidene)-3,5-dihydro-4H-imidazol-4-ones

A reaction of 3-allyl- and 3-phenylthiohydantoins with 1,5-diphenyl- and 1-phenyl-substituted 3-formyl-2-pyrazolines was used to obtain a series of 5-(pyrazolin-3-ylmethylidene)-2-thioxotetrahydro-4H-imidazol-4-ones, the subsequent alkylation of which with methyl iodide or ethyl chloroacetate gave the corresponding 2-alkylthio-5-(pyrazolin-3-ylmethylidene)-3,5-dihydro-4H-imidazol-4-ones in the yields from 30 to 77%. The oxidation of (5Z)-3-phenyl-5-[(1,5-diphenylpyrazolin-3-yl)methylidene]-2-methylsulfanyl-4,5-dihydroimidazol-4-one with lead tetraacetate led to the corresponding pyrazole in 48% yield.