Method For Oxidative Cleavage Research Articles

Regioselective oxidative cleavage of conjugated dienes to access α,β-unsaturated nitriles

A highly regioselective oxidative cleavage method has been developed for the synthesis of α,β-unsaturated nitriles and N-15 atom labeled α,β-unsaturated nitriles from unsymmetric conjugated dienes and ammonium salts.

Sub-tropical benthic/epiphytic dinoflagellates of Aotearoa New Zealand and Rangitāhua Kermadec Islands

Temperatures and temperature anomalies have been increasing in the sub-tropical regions of Aotearoa New Zealand and these changes may impact on harmful algal bloom (HAB) events. Benthic and epiphytic dinoflagellates, particularly the toxin producers, are the focus of this study as it is predicted that under future climate conditions they may produce more toxins or marine animals may become more susceptible to them. The results of past expeditions to Rangitāhua Kermadec Islands and sampling trips to Northland, Aotearoa New Zealand, are summarised and the results of the most recent trips to both regions are presented. The macroalgal habitats of the dinoflagellates are also characterised. Dinoflagellate species not previously identified in Rangitāhua include Coolia canariensis, C. palmyrensis, and C. tropicalis, all identified by DNA sequencing of the large subunit ribosomal RNA region. Gambierdiscus polynesiensis was again isolated and produced 44-methylgambierone and gambierone, and one isolate produced ciguatoxins, the cause of Ciguatera Poisoning. An Ostreopsis tairoto isolate, as analysed by the oxidative cleavage method, produced a palytoxin (PLTX)-like amine oxidation fragment, but when analysed for PLTX-like analogues using a new intact method none were detected indicating an ‘unknown’ PLTX-like compound is produced by this isolate. Isolates of O. cf. siamensis (Ostreopsis sp. 9), collected in Northland, were also analysed using the oxidative cleavage method, with the common PLTX-like amine fragment and the amide fragment corresponding to bishomoPLTX detected in all isolates. Again, the intact method indicated no detections in the isolates, again suggesting an unknown compound was being produced by these isolates. Prorocentrum hoffmannianum isolates produced okadaic acid (OA) and isoDTX-1 and P. lima isolates produced OA, DTX-1, and isoDTX-1. It is expected that new species of potentially harmful, benthic dinoflagellates will continue to be recorded in Aotearoa New Zealand and the results from Rangitāhua provide a guide to the HAB species to expect in sub-tropical Northland as the oceans continue to warm.

Analysis of total microcystins and nodularins by oxidative cleavage of their ADMAdda, DMAdda, and Adda moieties

Microcystins (MCs) and nodularins (NODs) exhibit high structural variability, including modifications of the Adda (3S-amino-9S-methoxy-2S,6,8S-trimethyl-10-phenyldeca-4E,6E-dienoic acid) moiety. Variations include 9-O-desmethylAdda (DMAdda) and 9-O-acetylDMAdda (ADMAdda) which, unless targeted, may go undetected. Therefore, reference standards were prepared of [ADMAdda5]MCs and [DMAdda5]MCs, which were analyzed using multiple approaches. The cross-reactivities of the [DMAdda5]- and [ADMAdda5]MC standards were similar to that of MC-LR when analyzed with a protein phosphatase 2A (PP2A) inhibition assay, but were <0.25% when analyzed with an Adda enzyme-linked immunosorbent assay (ELISA). Oxidative cleavage experiments identified compounds that could be used in the analysis of total MCs/NODs in a similar fashion to the 2R-methyl-3S-methoxy-4-phenylbutanoic acid (MMPB) technique. Products from oxidative cleavage of both the 4,5- and 6,7-ene of Adda, DMAdda and ADMAdda were observed, and three oxidation products, one from each Adda variant, were chosen for analysis and applied to three field samples and a Nostoc culture. Results from the oxidative cleavage method for total Adda, DMAdda, and ADMAdda were similar to those from the Adda-ELISA, PP2A inhibition, and LC-MS/MS analyses, except for the Nostoc culture where the Adda-ELISA greatly underestimated microcystin levels. This oxidative cleavage method can be used for routine analysis of field samples and to assess the presence of the rarely reported, but toxic, DMAdda/ADMAdda-containing MCs and NODs.

Hydroxyl radicals-mediated oxidative cleavage of the glycosidic bond in cellobiose by copper catalysts and its application to low-temperature depolymerization of cellulose

As the most abundant source of biomass in nature for sustainable production of fuels and chemicals, efficient depolymerization of cellulose under mild conditions, due to the difficulty in selective cleavage of its β-1,4-glycosidic bonds, still remains challenging. Here, we report a novel method for oxidative cleavage of the glycosidic bonds by free radicals. Probed by the cellobiose reaction, it was found that ·OH radicals, generated from the decomposition of H2O2 catalyzed by CuSO4 or CuO/SiO2, were efficient for selective conversion of cellobiose to glucose and gluconic acid at a low temperature of 333 K, and their selectivities reached 30.0% and 34.6%, respectively, at 23.4% cellobiose conversion. Other radicals, such as ·SO4−, also exhibited high efficacy in the cellobiose reaction. Mechanistic studies suggest that the oxidative cleavage of the β-1,4-glycosidic bond by the free radicals involve formation of the carbon radical intermediate via abstraction of the H atom dominantly at the C1 position. Following this oxidative mechanism, treatment of microcrystalline cellulose with ·OH by impregnation with H2O2 and CuSO4 catalyst at 343 K led to significant enhancement in its hydrolysis efficiency. These results demonstrate the effectiveness of this new method in the oxidative cleavage of glycosidic bonds, and its viability for the efficient depolymerization of cellulose at low temperatures, which can be further improved, for example, by exploring new free radicals and optimizing their reactivity and selectivity.

Copper-catalyzed demethylative esterification of arylmethylketones: a new route for the synthesis of benzocaine

An efficient method for oxidative cleavage of C(CO)–C bonds of ketones has been developed. This procedure enables activated methyl ketones to react with tetraethyl orthosilicate for generation of the corresponding methyl esters using copper as the catalyst. Primary mechanistic studies revealed that in contrary to other related studies, the involvement of the aldehyde as the intermediate of this reaction is highly probable. Interestingly, this study provides an unprecedented positive effect of the elemental sulfur upon this oxidative esterification reaction. As an application of our method, we have reported a two-step procedure for the synthesis of benzocaine. The second step of this procedure involves a highly selective reduction in nitro group in the presence of ester functionality.

ChemInform Abstract: Benzylidene Acetal Protecting Group as Carboxylic Acid Surrogate: Synthesis of Functionalized Uronic Acids and Sugar Amino Acids.

Direct oxidation of the 4,6-O-benzylidene acetal protecting group to C-6 carboxylic acid has been developed that provides an easy access to a wide range of biologically important and synthetically challenging uronic acid and sugar amino acid derivatives in good yields. The RuCl3 -NaIO4 -mediated oxidative cleavage method eliminates protection and deprotection steps and the reaction takes place under mild conditions. The dual role of the benzylidene acetal, as a protecting group and source of carboxylic acid, was exploited in the efficient synthesis of six-carbon sialic acid analogues and disaccharides bearing uronic acids, including glycosaminoglycan analogues.

Benzylidene Acetal Protecting Group as Carboxylic Acid Surrogate: Synthesis of Functionalized Uronic Acids and Sugar Amino Acids.

Direct oxidation of the 4,6-O-benzylidene acetal protecting group to C-6 carboxylic acid has been developed that provides an easy access to a wide range of biologically important and synthetically challenging uronic acid and sugar amino acid derivatives in good yields. The RuCl3 -NaIO4 -mediated oxidative cleavage method eliminates protection and deprotection steps and the reaction takes place under mild conditions. The dual role of the benzylidene acetal, as a protecting group and source of carboxylic acid, was exploited in the efficient synthesis of six-carbon sialic acid analogues and disaccharides bearing uronic acids, including glycosaminoglycan analogues.

Mechanism-specified 5-exo termini differentiation of a C32-desmethyl C28–C34 aplyronine A analog segment

A new mild, high yielding oxidative cleavage method allows access to a critical lactone aplyronine A analog precursor. Enhanced termini selectivity is achieved, granting access to a previously unavailable C28–C34 C-32-desmethyl actin binding tail fragment via vinyl sulfone polypropionate methodology.

Palladium-Catalyzed Synthesis of 3-Acylated Indoles Involving Oxidative Cross-Coupling of Indoles with α-Amino Carbonyl Compounds

A new and selective C-N bond oxidative cleavage method to 3-acylated indoles by Pd-catalyzed oxidative cross coupling of indoles with α-amino carbonyl compounds has been developed; moreover, one-pot synthesis of 3-acylated indoles from 2-ethynylanilines and α-amino carbonyl compounds has also been established. Importantly, the products 3-acylated indoles can be used to construct polyheterocyclic compound, which can be employed as efficient probes for Hg(2+) and Fe(3+).

Mild Oxidation of Oxime Derivatives with KMnO4 in Ionic Liquid Media

AbstractIn this research, potassium permanganate in the presence of a catalytic amount of [bmim]Br under solvent free conditions is used as an efficient and chemoselective method for oxidative cleavage of some oximes to corresponding carbonyl compounds. This experiment was carried out in mild conditions without any further oxidation of aldehydes to corresponding acids.

Deoximation of Ketoximes to Ketones with Ammonium Chlorochromate/Montmorillonite K10 in Dichloromethane

A convenient, mild and efficient method for oxidative cleavage of ketoximes to their parent carbonyl compounds with ammonium chlorochromate (ACC) / montmorillonite K10 in dichloromethane at room temperature is described

Activated Iodosylbenzene Monomer as an Ozone Equivalent: Oxidative Cleavage of Carbon−Carbon Double Bonds in the Presence of Water

Reported here for the first time are the developments of an efficient method for oxidative cleavage of carbon−carbon double bonds yielding carbonyl compounds by using aryl-λ3-iodanes, which involve a combination of iodosylbenzene and HBF4 in the presence of water. The method serves as a safety alternative to ozonolysis. The oxidative cleavage of olefins probably involves the hitherto unknown direct vicinal dihydroxylations of double bonds with aryl-λ3-iodanes and the subsequent oxidative glycol fissions. Cyclic (cyclopentenes, cyclohexenes, etc.) and acyclic olefins are cleaved smoothly under our conditions. In the reaction of electron-deficient styrenes such as m-nitrostyrene, intermediate formation of the corresponding epoxide was detected. A variety of aryloxiranes also undergo an oxidative cleavage of the epoxide rings under our conditions, and aromatic aldehydes were obtained in good yields

Oxidative deprotection of trimethylsilyl ethers under solvent-free conditions using K2S2O8 in the presence of catalytic amount of [bmim]Br

Potassium persulfate in the presence of a catalytic amount of ionic liquid [ bmim ]Br under solvent-free conditions is used as an efficient and convenient method for oxidative cleavage of trimethylsilyl ethers to the corresponding carbonyl compounds.

Lauric acid is desaturated to 12:1n-3 by hepatocytes and rat liver homogenates.

Lauric acid desaturation was investigated and described in liver homogenates and in cultured rat hepatocytes. The identification of the desaturated product of lauric acid has been performed using the oxidative cleavage method, and we showed that the obtained monoene was mainly 12:1n-3. This result suggests that lauric acid desaturation could be the first step in the biosynthesis of alpha-linolenic acid in animal cells.

An Improved Oxidative Cleavage Method for Large Scale Preparation of Some Acid‐Labile Aglycones from Glycosides

AbstractA practical method for large‐scale preparation of acid‐labile aglycones including protopanaxadiol, protopanaxatriol, cycloastragenol, and jujubogenin from the corresponding glycoside containing fraction was developed. The key point of this improved method is to generate and maintain the critical reaction conditions, anhydrous and strongly basic, in situ. This effort over comes the weakness of the reported method for oxidative cleavage of glycones and scales up the preparation of these acid‐labile aglycones for further studies.

A convenient, mild method for oxidative cleavage of alkenes with Jones reagent/osmium tetraoxide

Oxidative scission of alkenes is used for preparation of carboxylic acids and ketones. The authors present a method for cleavage of terminal olefins to yield a carboxylic acid based on the realization that a catalytic amount of osmium tetraoxide chromate should convert an olefin via a diol to an acid and/or ketone. The authors believe that and the osmium is then reoxidized by the chromate, which also cleaves the 1,2-diol. 1 tab.