Oximino Group Research Articles

Molecular mechanism of the transformation of oxidized lignin to N-substituted aromatics.

The cleavage of C-C bonds in oxidized lignin model compounds is a highly effective methodology for achieving lignin depolymerization, as well the generation of N-substituted aromatics. Here, density functional theory calculations were performed to understand the mechanism of the transformation of an oxidized lignin model compound (ligninox) and hydroxylamine hydrochloride to N-substituted aromatics. The reaction was proposed to proceed via an energetically viable mechanism featuring the initial production of HOAc acting as proton bridge. According to our calculations, Z-type oxime is the major intermediate of the reaction, with an energy barrier of 22.9 kcal mol-1, owing to the weak interactions between methoxy and oximino groups being stronger than that of E-type oxime. Additionally, the hydroxy addition is the rate-determining step, with an energy barrier of 27.0 kcal mol-1. Moreover, the huge net energy change of Beckmann and abnormal Beckmann rearrangements is the main overall thermodynamic driving force for producing N-substituted aromatics from oximes. The theoretical results have provided a clear picture of how ligninox transforms into N-substituted aromatics and are expected to provide valuable theoretical guidance for lignin depolymerization.

Convenient synthesis of endo,endo- and endo,exo-bicyclo[3.3.1]nonane diamines

3,7-Diaminobicyclo[3.3.1]nonanes were synthesized starting from adamantane-2-on. endo,endo-3,7-Diaminobicyclo[3.3.1]nonane was obtained through Schmidt rearrangement of 3,7-bicyclo[3.3.1]nonane dicarboxylic acid. The endo,exo-isomer was synthesized by Schmidt rearrangement of 3-oximinobicyclo[3.3.1]nonane-7-carboxylic acid in acidic media following reduction of oximino group which was unprecedentedly stable in the Schmidt reaction conditions.

Polarity Umpolung Strategy for the Radical Alkylation of Alkenes.

Free radical mediated alkylation of alkenes is a challenging and largely unmet goal. Disclosed here is a conceptually novel "polarity umpolung" strategy for radical alkylation of alkenes using a portfolio of easily accessed, difunctional alkylating reagents. This strategy is achieved by substituting inherently nucleophilic alkyl radicals with electrophilic sulfone-bearing surrogates, thus inverting the usual mode of reactivity. Along with alkylation, either an heteroaryl or oximino group is concurrently incorporated into the alkenes by a consecutive docking and migration process, leading to valuable products. The reaction displays a broad functional-group tolerance under mild reaction conditions. The protocol opens new vistas for the late-stage modification of complex natural products and drug molecules containing alkene moieties.

Polarity Umpolung Strategy for the Radical Alkylation of Alkenes

AbstractFree radical mediated alkylation of alkenes is a challenging and largely unmet goal. Disclosed here is a conceptually novel “polarity umpolung” strategy for radical alkylation of alkenes using a portfolio of easily accessed, difunctional alkylating reagents. This strategy is achieved by substituting inherently nucleophilic alkyl radicals with electrophilic sulfone‐bearing surrogates, thus inverting the usual mode of reactivity. Along with alkylation, either an heteroaryl or oximino group is concurrently incorporated into the alkenes by a consecutive docking and migration process, leading to valuable products. The reaction displays a broad functional‐group tolerance under mild reaction conditions. The protocol opens new vistas for the late‐stage modification of complex natural products and drug molecules containing alkene moieties.

Synthesis, structure elucidation, and antifungal potential of certain new benzodioxole-imidazole molecular hybrids bearing ester functionalities.

BackgroundThe incidence of fungal infections is a growing serious global health burden. There is an urgent medical demand to acquire new antifungal drug-like compounds having azole nuclei to get rid of the drawbacks of the currently available azole antifungal agents.MethodsThe target compounds 5a-r were synthesized in a four-step reaction sequence using the appropriate acetophenone derivative as a starting material. The antifungal potential of the title compounds was assessed using DIZ and MIC assays according to the reported standard procedures.ResultsThe newly synthesized oximino esters 5a-r were identified with the aid of various spectroscopic approaches. Their assigned chemical structures were confirmed via single-crystal X-ray structure of compound 5o. The molecular structure of compound 5o was crystallized in the triclinic, P–1, a=9.898 (3) Å, b=10.433 (3) Å, c=11.677 (4) Å, α =86.886 (6)°, β =87.071 (7)°, γ =64.385 (6)°, V=1,085.2 (6) Å3, Z=2. The synthesized compounds 5a-r were in vitro evaluated for antifungal potential against four fungal strains. Compounds 5l and 5m bearing a trifluoromethylphenyl moiety showed the best anti-Candida albicans activity with minimum inhibitory concentration (MIC) value of 0.148 μmol/mL, while compound 5b displayed the best activity toward Candida tropicalis with MIC value of 0.289 μmol/mL. Compounds 5o and 5l were the most active congeners against Candida parapsilosis and Aspergillus niger, respectively.ConclusionSingle-crystal X-ray analysis of compound 5o confirmed without doubt the assigned chemical structures of the title compounds as well as confirmed the (E)-configuration of their oximino group. Compounds 5b, 5l, 5m, and 5o emerged as the most active compounds against the tested fungi and they could be considered as new antifungal lead candidates.

Visible-light-induced carbosulfonylation of unactivated alkenes via remote heteroaryl and oximino migration

An efficient visible-light photocatalytic protocol for the vicinal heteroarylsulfonylation and oximinosulfonylation of unactivated olefins is described. The addition of sulfonyl radicals to alkenes triggers the intramolecular migration of remote heteroaryl and oximino groups via CC bond cleavage. The transformation features a good functional group tolerance and a broad substrate scope. A variety of valuable heteroaryl- and oximino-substituted alkyl sulfones are obtained under mild conditions in synthetically useful yields.

Synthesis of 1,4,6,10-tetraazaadamantane quaternary derivatives

Methods for the preparation of stable 1,4,6,10-tetraazaadamantane quaternary derivatives were developed based on quaternization of a tertiary nitrogen atom in tris(β-oximinoalkyl)amines or isomeric 4,6,10-trihydroxy-1,4,6,10-tetraazaadamantanes. This process constitutes a convenient approach to the introduction of a hydrophilic 1,4,6,10-tetraazaadamantane moiety into lipophilic molecules in order to increase their solubility in water. 4,6,10-Trihydroxy-1,4,6,10-tetraazaadamantane N-oxide was synthesized by the oxidation of the tertiary nitrogen atom in the tris-oxime and subsequent intramolecular cyclotrimerization of the oximino groups. Quantum chemical calculations showed that the quaternization of the annular nitrogen atom led to a considerable stabilization of tetraazaadamantane framework as compared to the open-chain form of tris-oxime.

Synthesis of Unsymmetrically Substituted 4,6,10-Trihydroxy-1,4,6,10-tetra­azaadamantanes via Intramolecular Cyclization of Tris(β-oximinoalkyl)amines

The cyclotrimerization of oximino groups in unsymmetrically substituted tris(β-oximinoalkyl)amines was studied. A general approach to the synthesis of 4,6,10-trihydroxy-1,4,6,10-tetraazaadamantanes containing different substituents at bridgehead carbon atoms was developed from available aliphatic nitro compounds.

Synthesis and Bio-Spectral Studies of Co(II) Complex of 5-Chloro-2,4-Dihydroxy Butyrophenoneoxime (CDHBOX)

Co(II) complex of 5-chloro-2,4-dihydroxy butyrophenoneoxime (CDHBOX) was synthesized from 5-chloro-2,4-dihydroxy butyrophenoneoxime by using standard protocol, and characterized by elemental analyses, melting point determination and spectral data. The ML2 (metal/ligand) stoichiometry of the complex was determined by spectrophotometric and potentiometric studies, and mass spectral data. The value of stability constant of the complex was found to be 6.94x 108 while its standard free energy of formation is 12.155 kcal/mol at 27ºC. Beer’s law is obeyed in the concentration range 2-15 ppm of Co. The value of molar extinction coefficient and sensitivity as per Sandell’s scale were found to 3.35x 103 L.mol-1cm-1and 0.017 μg Co/cm2 respectively. The value of activation energy and the Arrhenius constant Arrhenius constant were found as 4.949 kjmol-1, 74.39. The IR studies reveal that the phenolic proton is lost on complexation and the oxygen of the phenolic (–OH) and nitrogen of the oximino (=NOH) groups coordinate with Co(II) ion. The electronic spectra and magnetic susceptibility measurement indicate that the complex is paramagnetic and tetrahedral in nature. The antimicrobial activity of different concentrations of ligand and its Co(II)-complex has been evaluated against Curvularia lunata, Fusarium oxysporum and Alternaria alternata fungi and Streproproteus, Staph, Escherchia coli, Klebsella, and pseudomonas bacteria. The results indicated that the ligand (CDHBOX) and its Co(II) complex have good anti-microbial properties.

ChemInform Abstract: Synthesis and Cytotoxic Activity of Derivatives of 6Z‐Acetylmethylenepenicillanic Acid tert‐Butyl Ester.

AbstractA dependence of the cytotoxic effect in relation to cancer and normal cells in vitro on the structure of the substituents and the syn and anti‐isomerism of the oximino group is established for the new compounds.

Design and synthesis of novel bis-oximinoalkanoic acids as potent PPARα agonists

Bis-oximinoalkanoic acid derivatives were designed and synthesized to aid in the characterization of selective PPARα agonists by replacing the oxazole ring with flexible oximino group in the lipophilic tail part of a previously reported compound 3. Selected compounds 9d and 9m showed excellent potency and high selectivity towards PPARα in vitro. These compounds found effective in reducing serum triglycerides (TG) in vivo.

Synthesis, characterization and XRPD studies of the bioactive complex of 2-hydroxy-3,5-dimethyl acetophenoneoxime (HDMAOX) with oxovanadium(IV)

The complex of 2-hydroxy-3,5-dimethyl acetophenoneoxime (HDMAOX, HL) with VO(IV) has been synthesized and characterized by different physical techniques. Infrared spectra indicate deprotonation and coordination of the phenolic OH, and nitrogen of the oximino group. Electronic spectra and magnetic susceptibility measurements support square-pyramidal geometry around the metal ion. The elemental analyses and mass spectral data indicate ML2 composition. Thermodynamic activation parameters were computed from the thermal data using the Coats and Redfern method. The crystal data for C20H24N2O5V are: tetragonal, space group P4/m, a = 11.76975 Å, b = 11.76975 Å, c = 18.89209 Å, V = 2617.06 A3, Z = 4. The free ligand (HDMAOX) and its oxovanadium complex have been tested in vitro against Alternaria alternate, Aspergillus flavues, Aspergillus nidulans and Aspergillus niger fungi and Streptococcus, Staph, Staphylococuss and Escherchia coli bacteria in order to assess their antimicrobial potential. The results indicate that the ligand and its metal complex have antimicrobial properties.

Syntheses based on α-azidooximes: II. Preparation of 6,7-dihydrotriazolopyrazinones from aliphatic nitro compounds

α-Azidooximes readily obtained from aliphatic nitro compounds were cleanly converted into previously unknown 6,7-dihydro[1,2,3]triazolo[1,5-a]pyrazin-4(5H)-ones via [3+2]-cycloaddition to dimethyl acetylenedicarboxylate and reduction of the oximino group in forming intermediates.

Synthesis, characterization and biological activity of complexes of 2-hydroxy-3,5-dimethylacetophenoneoxime (HDMAOX) with copper(II), cobalt(II), nickel(II) and palladium(II)

A new series of complexes of 2-hydroxy-3,5-dimethyl acetophenone oxime (HDMAOX) with Cu(II), Co(II), Ni(II) and Pd(II) have been prepared and characterized by different physical techniques. Infrared spectra of the complexes indicate deprotonation and coordination of the phenolic OH. It also confirms that nitrogen atom of the oximino group contributes to the complexation. Electronic spectra and magnetic susceptibility measurements reveal square planar geometry for Cu(II), Ni(II) and Pd(II) complexes and tetrahedral geometry for Co(II) complex. The elemental analyses and mass spectral data have justified the ML 2 composition of complexes. Kinetic and thermodynamic parameters were computed from the thermal decomposition data using Coats and Redfern method. The geometry of the metal complexes has been optimized with the help of molecular modeling. The free ligand (HDMAOX) and its metal complexes have been tested in vitro against Alternarie alternate, Aspergillus flavus, Aspergillus nidulans and Aspergillus niger fungi and Streptococcus, Staph, Staphylococcus and Escherchia coli bacteria in order to assess their antimicrobial potential. The results indicate that the ligand and its metal complexes possess antimicrobial properties.

3-Bromo-5-tert-butyl-2-(4-isopropylphenyl)-2-methoxycyclohexan-1-one oxime

In the title compound, C20H30BrNO2, the cyclo­hexa­none ring is in a sightly distorted chair form. The oximino group assumes an E configuration with the hydr­oxy group anti to the substituents at the C-2 position. Of the four substituents viz., tert-butyl, aryl, bromo and meth­oxy groups, the former two occupy equatorial positions and the latter two are placed axially on the cyclo­hexa­none ring.

Less common patterns of reduction of some oximes

Most oximes are reduced in a single, pH-dependent, four-electron wave, in which an amine is formed. Examples of reduction of some oximes, which differ from this general pattern, are reported. These different behaviors can be caused by changes in acid–base equilibria and in the rate of their establishment. Such changes can result from the role of strongly electron-withdrawing substituents, such as the cyano group. Alternatively the reduction pattern can be changed by a covalent hydration of the C N bond. This has been observed for compounds bearing a CF 3 group adjacent to the oximino group. Finally, a different reduction pattern can result from interposed acid–base reactions. The difference in such reactions cause different reduction patterns of two isomeric monoximes of 1-phenyl-1,2-propanedione.

Synthesis and spectra of aldehyde- and ketone-O-(2,5-dihydro-2-methoxy-5,5-dimethyl-1,3,4-oxadiazol-2-yl)oximes — Thermal sources of some methoxy(oximino)carbenes

Ten new oxadiazoline sources of methoxy(oximino)carbenes were synthesized by exchanging the acetoxy group of 2-acetoxy-2-methoxy-Δ3-1,3,4-oxadiazoline with an oximino group. The new compounds were characterized by means of spectroscopy and the formation of carbenes upon thermolysis of a few was demonstrated by means of interception with tert-butyl alcohol. The carbenes fragmented to form methoxycarbonyl and iminyl radicals.Key words: 2,2-dioxyoxadiazoline, methoxy(oximino)carbene, oxadiazole, radical pair, rearrangement.

Discussion of the Physicochemical Effects of Modifiers on the Extraction Properties of Hydroxyoximes. A Review

The physicochemical aspects of hydroxyoxime modification with various modifiers containing oxygen atoms are discussed. This kind of modification is unique to hydroxyoxime reagents, which form weak intramolecular and intermolecular hydrogen bonds. These bonds can easily be destroyed not only by modifier molecules (alcohols, alkylphenols, and esters) but also by solvating diluents. Alcohols are stronger modifiers than alkylphenols. The drawback of these modifiers is their strong self‐association, which is eliminated in esters and sterically hindered alcohols. The extraction properties of strong hydroxyoxime extractants can also be modified by adding weak reagents (hydroxyoximes or β‐diketones), which form co‐associates with strong extractants. The use of sterically hindered esters seem rational for two reasons: they inhibit hydroxyoxime adsorption at the hydrocarbon/water interface with oximino group penetrating the aqueous layers; and they show negligible adsorption. Due to these phenomena, hydroxyoxime extractants are more stable, and a retardation of the extraction is not observed in the presence of hindered esters. There is currently no general explanation of the chemistry of modification. Many published works focus only on the interactions of modifiers with extractants, neglecting the interactions with metal complexes. In order to achieve a substantial progress in our understanding of the phenomenon of modification, interactions between complexes and modifiers must be studied and explained.

Contribution to the alkaline degradation of cefepime

Deviations of the value of the rate constant for borate anions of the first step in the degradation of the antibiotic cefepime from Bronsted relation and deviations from i= f(pH) plots in voltammetric reductions of the oximino group led to investigation of the kinetics of degradation of cefepime in ammonia, borate, CHES and glycine buffers pH 9.3 using UV–visible spectra. Presence of at least two consecutive processes was detected and an interaction of cefepime with glycine has been proved. Identification of intermediates is under investigation.

Functional silanes: crosslinkers for silicone elastomers

Hydrolyzable functional silanes are used as silicone elastomer crosslinkers. The hydrolysis, triggered by air moisture, leads to crosslinking of linear polymer chains to three-dimensional networks. The properties of these elastomers depend on the silane structure. The influence of the structure has been studied for RSi(OR´)3 silanes with R = Me, Et, Pr, Bu, Pentyl (Pe), Vinyl (Vi) and Phenyl (Ph) for hydrolyzable acetoxy or oximino groups. Reactivity differences have been observed. The cure kinetics follows the order Vi > Ph ~ Me > Et > Pr > Bu > Pe leading to a decrease in surface curing rate from Vi to Pe. The cure thermodynamics, i.e. completeness of cure, follows the order Me > Et > Pr > Bu > Pe and Vi > Ph leading to a decrease in the crosslink density from Me to Pe. The lower degrees of cure are related to steric and inductive effects of the functional groups. Oximinosilanes showed a lower reactivity compared to acetoxysilanes, because of a Si—ON bond being more stable than a Si—OAc bond. This also leads to slower surface cure and lower crosslink density. Organometallic tin used for the catalysis of oximinosilane systems gave results similar to organometallic titanium. For acetoxysilane systems, the titanium system was found to be more efficient. Silicone materials tailored to specific requirements can be designed. So the cure rate, release and mechanical properties can be adjusted with the selection of appropriate silanes.