Mass spectral investigations on trichothecene mycotoxins. III. Synthesis, characterization and applications of pentafluoropropionyl and trifluoroacetyl esters of simple trichothecenes

The pentafluoropropionyl, (PFP) and trifluoroacetyl (TFA) esters of several naturally occurring and synthetically modified simple trichothecenes were synthesized in nanogram amounts and characterized. Optimum conditions for the gas chromatographic (GC) separation of these derivatives and their analysis by negative ion chemical ionization (NICI) mass spectrometric technique were determined. These perfluoroacyl derivatives under the NICI conditions undergo limited but characteristic fragmentations similar to the fragmentations of heptafluorobutyryl esters of trichothecenes under the same conditions. Characteristic ions for the specific detection and accurate quantification of these PFP and TFA derivatives were chosen. Preliminary results indicated that the PFP derivatives are better suited for the analysis of simple trichothecenes by GC-NICI-MS technique. Ultra trace (0.5-2.0 pg) amounts of these PFP derivatives were detected by the developed procedure.     

Application of differential reactivity towards synthesis of lamellarin and 8-oxoprotoberberine derivatives: Study of photochemical properties of aryl-substituted benzofuran-8-oxoprotoberberines

A unique differential reactivity between dihydroisoquinolines and 3-nitrocoumarins was observed and was exploited for the efficient construction of lamellarins and their isomeric benzofuran-8-oxoprotoberberine derivatives under acid-catalyzed or base-promoted conditions. Further, these prepared aryl-substituted benzofuran-8-oxoprotoberberine derivatives bearing electron-donating substituents on benzofuran moiety are found to be benchtop stable but light-sensitive, and can undergo oxidative ring-opening reaction to give the corresponding keto products when exposed to visible light under aerobic conditions.     

Silica sulfuric acid mediated synthesis of naphtho[2,1-b]furan derivatives and development of one-pot multicomponent synthesis of substituted pyrazole derivatives

Silica sulfuric acid (SSA) mediated synthesis of naphtho[2,1-b]furan derivatives starting from β-nitrostyrene derivatives and β-naphthol derivatives under solvent-free conditions have been developed. The scope of SSA as a heterogeneous catalyst is extended to one-pot multicomponent reaction for the synthesis of functionalized pyrazole derivatives under solvent-free conditions from readily available β-nitrostyrene derivatives, acetyl acetone, and hydrazine hydrate. The synthetic methods have significant advantages such as solvent-free conditions, simple operation, shorter reaction times, ease and clean isolation procedures, and very good yields of products.     

Biodegradation of Pyridine and Pyridine Derivatives by Soil and Subsurface Microorganisms

Abstract

Large amounts of aromatic compounds are produced by various industries and two thirds of these are heterocyclic chemicals. Compared with the extensive information available on microbial degradation of homocyclic aromatic compounds, relatively little is known on the transformation and biodegradation of heterocyclic chemicals in soil. Recent concerns about the persistence of hazardous pollutants have led to a renewed interest in the biodegradation of heterocyclic compounds. Hence, we investigated the microbial degradation of pyridine and some of its alkylated derivatives under aerobic and anaerobic conditions in groundwater, subsurface sediment, and soil. Results of the investigation revealed that these compounds were degraded predominantly under aerobic conditions and, to a lesser extent, under anaerobic conditions, with nitrate or sulfate serving as electron acceptors. In groundwater polluted with various pyridine derivatives, biodegradation was limited by the absence of oxygen. Therefore, we conclude that, under appropriate conditions, bioremediation is a potentially feasible method for the clean-up of environments contaminated with heterocyclic chemicals and, in particular, pyridine derivatives.     

Lewis acid catalyzed cascade reactions of diarylvinylidenecyclopropanes and 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers

The reactions of vinylidenecyclopropanes 1 with 1,1,3-triarylprop-2-yn-1-ols or their methyl ethers 2 in the presence of a Lewis acid selectively produce 4-dihydro-1H-cyclopenta[b]naphthalene derivatives 3 or 1,2,3,8-tetrahydrocyclopenta[a]indene derivatives 4 depending on the substituents on the cyclopropane. Good to high yields are obtained under mild conditions. A plausible cascade Meyer-Schuster rearrangement and Friedel-Crafts reaction mechanism has been proposed. Moreover, novel functionalized methylenecyclobutene derivatives 5 could also be obtained in moderate to good yields under similar conditions when strongly electron-donating methoxy groups were introduced into the benzene rings of 2.     

N-Isocyaniminotriphenylphosphorane as an Efficient Reagent for the Synthesis of Disubstituted 1,3,4-Oxadiazoles Via In-Situ Generation of Sterically Congested Iminophosphorane Derivatives

Abstract

Reaction of N-isocyaniminotriphenylphosphorane with benzaldehyde derivatives in the presence of 3-phenyl-2-propynoic acid and secondary amines proceeds smoothly at room temperature and under neutral conditions to afford sterically congested 1,3,4-oxadiazole derivatives in high yields. The reaction proceeds smoothly and cleanly under mild conditions and no side reactions are observed.     

An easy stereoselective access to beta,gamma-aziridino alpha-amino ester derivatives via mannich reaction of benzophenone imines of glycine esters with N-sulfonyl alpha-chloroaldimines

Mannich-type addition of benzophenone imine glycinates across newly synthesized N-(p-toluenesulfonyl) alpha-chloroaldimines afforded gamma-chloro-alpha,beta-diamino ester derivatives with moderate diastereoselectivity as separable mixtures of anti and syn diastereomers. The gamma-chloro-alpha,beta-diamino esters were efficiently cyclized under basic conditions to the corresponding beta,gamma-aziridino alpha-amino ester derivatives, representing a new class of conformationally constrained heterocyclic alpha,beta-diamino acid derivatives. The relative configuration of the aziridines was determined via X-ray diffraction analysis. Mechanisms and intermediate transition states to explain the stereochemical outcome of the Mannich reaction with different substrates or under different conditions are proposed. The synthetic importance of the beta,gamma-aziridino alpha-amino ester derivatives is demonstrated by their conversion into the corresponding Boc-protected derivatives and ring opening reactions to alpha,beta-diamino esters and a gamma-amino alpha,beta-unsaturated amino ester.     

可见光诱导烷基羧酸及其衍生物的脱羧偶联反应研究进展

烷基羧酸广泛存在于自然界之中,科研工作者一直致力于开发以来源丰富的烷基羧酸及其衍生物作为起始原料的反应.烷基羧酸及其衍生物在可见光氧化还原作用下可以高效地生成烷基自由基,从而在温和条件下用于构筑各类化学键.以可见光催化烷基羧酸及其衍生物的脱羧自由基反应类型为线索,系统地综述了近年来在可见光条件下烷基羧酸及其衍生物的脱羧官能团化反应研究进展.     

A Green Route for the One‐Pot Synthesis of 1,2‐Disubstituted Benzimidazoles Using Iron(III) Phosphate under Solventless Conditions

1,2‐Disubstituted benzimidazoles are selectively synthesized in high yields under extremely mild conditions via the condensation of o‐phenylenediamine derivatives with aldehyde derivatives using catalytic amount of iron(III) phosphate under solvent‐free conditions. The use of readily available iron(III) phosphate as a reusable and recyclable catalyst makes this process quite simple, convenient, and environment‐friendly.     

Novel thermal reaction of Fischer carbene complexes with imines: synthesis of beta-methoxy allylic amine derivatives

[formula: see text] Alkyl-substituted chromium Fischer carbene complexes were found to react with various N-tosylimines to give beta-methoxy allylic amine derivatives under thermal conditions. This result is essentially distinct from the photochemical outcome in which beta-lactam derivatives are obtained.     

1,2-oxazine chemistry—I : Synthetic approaches to tetrahydro-1,2-oxazines

The synthesis of a series of N-carbethoxytetrahydro-1,2-oxazines, by the reaction of 1,4-dibromobutane derivatives with N-hydroxyurethane under basic conditions, and their reduction to N-Me derivatives is described. Stereochemical and mechanistic points of interest in these reactions are discussed.     

Investigations in the field of benzimidazole derivatives

The bromination of 1, 3-dialkyl-2-iminobenzimidazolines by the action of potassium bromate and hydrobromic acid leads via the perbromides formed intermediately to 5(6)-monobromo derivatives and, further, to 5,6-dibromoimines. Under these conditions, 1-alkyl-2-aminobenzimidazoles form mixtures of 5- and 6-monobromo-substituted derivatives which, on further bromination, are converted into 5,6-dibromo and, under more severed conditions, into 4,5, 6-tribromo derivatives.For part XX, see [1].     

1,4‐Cyclohexadienes—Easy Access to a Versatile Building Block via Transition‐Metal‐Catalysed Diels–Alder Reactions

1,4‐Cyclohexadiene derivatives are easily accessed via transition‐metal cycloadditions of 1,3‐dienes with alkynes. The mild reaction conditions of several transition‐metal‐catalysed reactions allows the incorporation of various functional groups to access functionalised 1,4‐cyclohexadienes. The control of the regiochemistry in the intermolecular cobalt‐catalysed Diels–Alder reaction is realised utilising different ligand designs. The functionalised 1,4‐cyclohexadiene derivatives are valuable building blocks in follow‐up transformations. Finally, the oxidation of the 1,4‐cyclohexadienes can be accomplished under mild conditions to generate the corresponding arene derivatives.     

One-carbon extrusion from carbohydrates via C1-alkoxy radical fragmentation. An easy access to erythrose and threose

Generation and fragmentation of the C1-alkoxy radicals of pyranose derivatives are nicely promoted by (diacetoxyiodo)benzene or lead tetraacetate in the presence of iodine catalyst under mild conditions to give the corresponding mixed-acetal formates which are further converted to the furanose derivatives by acid-catalysed transacetalization.     

Facile N-derivatization of alpha-amino esters and amides via benzotriazolylmethyl derivatives

Alpha-(N-substituted amino)esters were prepared in a two-step procedure from available unsubstituted alpha-amino esters. alpha-Amino esters are first converted into the corresponding N-benzotriazolylmethyl derivatives; in the second step, the benzotriazole group is substituted by various nucleophiles with or without the presence of a Lewis acid to give substituted alpha-amino esters in high overall yield under mild conditions with no signs of racemization. Boc-protected amino acids were converted into alpha-amino amides; subsequent deprotection allowed the conversion into N-substituted derivatives analogously to the alpha-amino esters, without racemization in high yields under mild conditions.     

N-Alkoxyl Templates for Diastereoselective Pyrrolidine Synthesis

Intramolecular cyclization of N-alkoxyl amines are studied for the stereoselective preparation of 2, 4-disubstituted pyrrolidine derivatives. Reduction of oximes under acidic conditions by NaBH3CN afforded the corresponding nucleophilic hydroxylamine derivatives,which subsequently cyclized via SN2‘ mechanism to give the desired N-alkoxyl pyrrolidines.     

Gadolinium triflate catalyzed alkylation of pyrroles: efficient synthesis of 3-oxo-2,3-dihydro-1H-pyrrolizine derivatives

Novel 2-alkylated pyrrole derivatives were synthesized regioselectively by Gd(OTf)₃ catalyzed addition reactions of pyrrole to substituted dimethyl 2-benzylidenemalonate derivatives under mild reaction conditions. 2-Alkylated pyrrole derivatives are used for the construction of the 3-oxo pyrrolizine skeleton. Intramolecular cyclization of alkylated pyrrole derivatives afforded new diastereoselective 3-oxo-2,3-dihydro-1H-pyrrolizine derivatives with good to high yields.     

2-Imidazolines. III (1). 1-Aryl- and 1-acyl-2-amino-(ormethoxy)-4,5-diamino-4,5-dihydroimidazoles. Synthesis and properties

Diimmonium salt (5) reacts with guanidines (6) and o-methylisoureas (7) affording 2-amino-4,5-dimorpholinoimidazolines (9) . 1-Aryl-2-amino-4,5-dimorpholinoimidazolines lose the amino functionality under mild acidic conditions with formation of 2-amino-5-morpholinoimidazole derivatives (10) whereas 1-acyl derivatives undergo under the same conditions a ring expansion process leading to pyrimidine derivatives (13) .     

Aerobic oxidation of N-alkylamides catalyzed by N-hydroxyphthalimide under mild conditions. Polar and enthalpic effects

The oxidation of N-alkylamides by O(2), catalyzed by N-hydroxyphthalimide (NHPI) and Co(II) salt, leads under mild conditions to carbonyl derivatives (aldehydes, ketones, carboxylic acids, imides) whose distribution depends on the nature of the alkyl group and on the reaction conditions. Primary N-benzylamides lead to imides and aromatic aldehydes at room temperature without any appreciable amount of carboxylic acids, while under the same conditions nonbenzylic derivatives give carboxylic acids and imides with no trace of aldehydes, even at very low conversion. These results are explained through hydrogen abstraction by the phthalimide-N-oxyl (PINO) radical, whose reactivity with benzyl derivatives is governed by polar effects, so that benzylamides are much more reactive than the corresponding aldehydes. The enthalpic effect is, however, dominant with nonbenzylic amides, making the corresponding aldehydes much more reactive than the starting amides. The importance of the bond dissociation energy (BDE) of the O-H bond in NHPI is emphasized.     

Synthesis of alkylated methylene bisphosphonates via organothallium intermediates

Thallium(I) derivatives of esterified methylene bisphosphonates can be readily obtained by treating the latter with thallium(I) ethoxide under anhydrous conditions. Alkylation of the thallium(I) derivatives by a range of primary alkyl iodides takes place smoothly, and significantly higher yields are obtained than for the corresponding reactions with lithio or sodio derivatives.