Cycloaddition reactions of carbohydrate derivatives. Part 8: Intramolecular cycloaddition of nitrilimines derived from sugars

Nitrilimines containing a carboncarbon double bond were prepared in several steps from 2,3,4-tri-O-benzyl-d-xylose, d-ribose and l-arabinose derivatives and their intramolecular 1,3-dipolar cycloaddition reactions were studied. The results were examined with molecular modelling and compared with the literature data for similar cycloadditions.     

d-Xylose and l-Arabinose-based surfactants: Synthesis,reactivity and physico-chemical properties

The valorization of d-xylose and l-arabinose towards the formation of non-ionic surfactants is here described. Several processes are employed involving telomerization, glycosylation and phosphorylation reactions. Various structures of surfactants are given with respectively their amphiphilic properties.     

Efficient O-glycosylation of diethyl oxoglutarate via 1,2-O-sulfinyl derivatives

1,2-O-Sulfinyl derivatives of d- and l-arabinose, d-xylose and d-glucose treated by potassium anion of diethyl oxoglutarate gave, exclusively, the corresponding O-glycosides in 92-97% yields.     

Synthesis of 2-fluoro-substituted and 2,6-modified purine 2′,3′-dideoxy-2′,3′-difluoro-d-arabinofuranosyl nucleosides from d-xylose

A series of novel purine-modified 2′,3′-dideoxy-2′,3′-difluro-D-arabinonucleosides, including fluorinated analogs of fludarabine and nelarabine, have been prepared via anion glycosylation reactions of salts of 2-fluoropurine derivatives with the glycosyl bromide. A short and efficient synthetic route to the carbohydrate precursor 5-O-benzoyl-2,3-difluoro-α-d-arabinofuranosyl bromide was developed in five steps from d-xylose. Improved synthesis of methyl 5-O-benzoyl-2,3-difluoro-α-d-arabinofuranoside based upon the study of diethylaminosulfur trifluoride (DAST)-reactions with 5-O-protected methyl D-xylosides was explored using mild reaction conditions on the key step. New peculiarities for selective fluorinations of 5-O-benzoylated α- and β-D-pentofuranosides with DAST leading to the formation of mono and difluoro-furanoside derivatives are reported.     

Sulfuric acid immobilized on silica: an efficient reusable catalyst for the synthesis of O-isopropylidene sugar derivatives

Sulfuric acid immobilized on silica proved to be an efficient catalyst for the synthesis of O-isopropylidene sugar derivatives from reducing sugars. The method is very simple and economic for large-scale synthesis in which the catalyst is recovered and reused several times. Reactions with d-glucose, d-galactose, d-mannose, l-rhamnose, l-arabinose, d-xylose and l-sorbose led to the formation of the corresponding thermodynamically stable di-O- and/or mono-O-isopropylidene derivatives in good to excellent yields.     

Regio- and stereoselective syntheses of l-pentose derivatives from l-arabinose

Novel l-arabinose, l-ribose, 2-deoxy-l-ribose and 2-fluoro-2-deoxy-l-arabinose derivatives were synthesized from readily available l-arabinose. Different synthetic routes to methyl 3,5-di-O-acylated-l-arabino(ribo)furanosides as valued intermediates for the preparation of C-2 functionalized l-pentoses were investigated via regioselective transformations of 1,2-di-O-acetyl-3,5-di-O-pivaloyl-l-arabinofuranose, and selective acylation of methyl l-arabinofuranoside with 4-chlorobenzoyl or pivaloyl chloride. Short three-five-step syntheses of methyl 2-deoxy-α-l-ribofuranoside, its 3,5-di-O-acyl derivatives, valuable precursors for preparation of antiviral 2′-deoxy-l-nucleosides, were accomplished via simple and efficient reduction of methyl 2-O-mesyl-l-arabinofuranoside with L-Selectride or tandem reaction involving a complex hydride 2-deoxygenation/acylation of intermediate 2-deoxysugar. A new synthesis of 2′-deoxy-2′-fluoro-β-l-arabinofuranosyl thymine (l-FMAU) was performed using a mild fluorination of protected l-ribofuranoside and a novel sequence of conversions for the preparation of 2-deoxy-2-fluoro-l-arabinofuranoside derivatives.     

NMR Characterization of Substituted Aromatic Poly (Ether Sulofone)s

Abstract

The synthesis of a variety of substituted bisphenol A polysulfones, including nitro, amino, aminomethyl, ethyl, and methyl derivatives, is described. Nuclear magnetic resonance (NMR) (both proton and carbon, and several 2-D experiments) data confirm conclusions on the substitution site based on arguments on inductive effects in the phenyl rings. The proton ortho to the oxygen in the bisphenol A (BPA) residue is replaced in electrophilic substitution reactions. The degree of substitution was also calculated from the NMR results. The ethyl and methyl derivatives were expected, from the starting reactants, to each have a BPA ring substituted. The NMR data showed that, on the average, this is true. The nitro derivative also has substitution in every BPA ring, while the amino and aminomethyl derivatives have only intermittent BPA rings substituted. Measured degrees of substitution (DS) varied from 0.11 to 2.25.     

Synthesis of anomerically pure vinyl sulfone-modified pent-2-enofuranosides and hex-2-enopyranosides: a group of highly reactive Michael acceptors for accessing carbohydrate based synthons

Syntheses of the benzyl or the trityl protected α- and β-anomers of vinyl sulfone-modified pent-2-enofuranosides have been initiated by the ring opening of the suitably masked methyl α-lyxofuranosyl-epoxide or methyl β-ribofuranosyl-epoxide or by the nucleophilic displacement of the leaving groups in benzyl protected 3-O-tosyl xylofuranoside and 3-O-mesyl ribofuranoside by p-thiocresol. In case of the latter set of starting materials, α- and β-methyl glycosides formed in almost equal ratio only from the derivatives of d-xylose. For the synthesis of α- and β-anomers of vinyl sulfone-modified hex-2-enopyranosides, a d-glucose derivative was selected over a d-allose derivative as the starting material because the former almost exclusively produced the required methyl pyranosides whereas the latter produced a mixture. All sulfides were converted to vinyl sulfone-modified carbohydrates by the sequential application of oxidation, mesylation and base induced elimination reactions.     

Theoretical study on the hydrogen abstraction reactions from hydrazine derivatives by H atom

The hydrogen abstraction reactions from hydrazine and its methyl derivatives by the H atom have been investigated theoretically by using CBS-QB3//DSD-BLYP-D3(BJ)/Def2-TZVP quantum chemical calculations and transition state theory calculations coupled with various tunneling correction methods. Both the products and transition state energies of the hydrogen abstraction from the amino group were stabilized by the methyl group substitution. The substitution effect on the ^αN site was two times larger than that on the ^βN site. On the other hand, the substitution effect was negligible on the hydrogen abstraction from the methyl group. The overall rate coefficients of N₂H₄ + H reaction calculated by canonical variational transition state theory with the small-curvature tunneling correction agreed well with previously reported values, but those of CH₃NHNH₂/(CH₃)₂NNH₂ + H were slightly lower than a previous experimental value. The product-specific rate coefficients have been proposed for the kinetics modeling of these fuels’ combustion.     

Temperature and solvent dependent NMR studies on mangiferin and complete NMR spectral assignments of its acyl and methyl derivatives

By employing concerted 1 and 2D NMR techniques, exact NMR spectral assignments have been made of the acyl (2-7) and methyl (8 and 9) derivatives of mangiferin (1) isolated from the leaves of Bombax ceiba. Derivatives 2, 8 and 9 have been reported in literature, while 3-7 represent new compounds. The acetates 2 and 3 were found to be unstable and were converted into the same penta-acetate 4 at room temperature. Extensive NMR studies on mangiferin (1) and its derivatives showed that H-4 exchanges with deuterium of the solvent molecule more easily. This exchange under acidic conditions occurred at that position (C-4) where electrophilic substitution reactions can easily take place. This is the first report describing the exchange of C-4 proton of mangiferin (1), or any other xanthone, with deuterium of solvent molecules.     

Synthesis of trihydroxylated pyrrolizidine and indolizidine alkaloids based on SmI2-induced reductive coupling of chiral nitrones with methyl acrylate

Synthesis of trihydroxylated pyrrolizidines, the enantiomer of 2-epihyacinthacine A₂ and indolizidine analogues of the natural alkaloids is reported. The key step of these syntheses is the stereoselective samarium diodide-induced coupling of the chiral nitrone prepared from d-ribose with methyl acrylate. The nitrone derived from d-ribose possessing C2/C3 syn configuration reacted with methyl acrylate in the presence of samarium diiodide in excellent yield and diastereoselectivity, with only the anti-diastereomer being detected.     

Hydrogen/deuterium exchange in gas phase reactions of anions with some alkyl phenyl ethers

The gas phase reactions of anions with methyl and ethyl phenyl ether have been studied by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry. ¹⁸O-Labelling has shown that part of the reactions of OH^- with methyl phenyl ether proceed via ipso-substitution, the main reaction channel being S_N2 substitution. Deuterium labelling has shown that extensive inter- and intramolecular hydrogen/deuterium exchange can precede the final substitution reaction. Hydrogen atoms originating from the methoxy substituent are involved in this exchange process. The reactions of anions with ethyl phenyl ether proceed mainly via an elimination mechanism. Deuterium labelling has shown that in some cases hydrogen/deuterium exchange takes place prior to elimination.     

环丙叉环丙烷——一个新的多功能有机合成子

介绍了一个新的多功能有机合成子环丙叉环丙烷及其衍生物的制备和反应，环 丙叉环丙烷现已可从环丙烷羧酸甲酯出发较大量地制备。其单取代衍生物亦可容易 地经对其进行去质子化-亲电取代而制备，环丙叉环丙烷的典型反应性能为：（1） 环丙烷环上四个亚甲基有增强了动力学酸度，易于去质子化；（2）中间双键对环 加成反应有很高活性；（3）环丙烷环上处于双键近端和远端的C-C单键可发生裂解 ；（4）在有些反应中，可同时表现出上述反应性能，介绍了环丙叉环丙烷及其衍 生物的一些反应：对中间C=C双键的[2+n]环加成反应、亲电和自由基加成反应、1 ，3-偶极环加成反应和过渡金属催化的反应。     

Laccase-Catalyzed Oxidation of Allylbenzene Derivatives: Towards a Green Equivalent of Ozonolysis

Laccase-based biocatalytic reactions have been tested with and without mediators and optimized in the oxidation of allylbenzene derivatives, such as methyl eugenol taken as a model substrate. The reaction primarily consisted in the hydroxylation of the propenyl side chain, either upon isomerization of the double bond or not. Two pathways were then observed; oxidation of both allylic alcohol intermediates could either lead to the corresponding α,β-unsaturated carbonyl compound, or the corresponding benzaldehyde derivative by oxidative cleavage. Such a process constitutes a green equivalent of ozonolysis or other dangerous or waste-generating oxidation reactions. The conversion rate was sensitive to the substitution patterns of the benzenic ring and subsequent electronic effects.     

Dextran derivatives

Conclusions 1. Acid chloride and carbodiimide methods for the synthesis of N-aminoacyl derivatives of carboxymethyldextran have been developed.2. Using these methods, derivatives of carboxymethyldextran containing residues of glycine esters (with different degrees of substitution) and residues of the methyl ester of L-histidine have been synthesized.3. A method for obtaining carboxymethyldextrans with different degrees of substitution has been developed.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 6, pp. 525–531, 1969     

Synthetic studies of venturicidins: stereoselective synthesis of the C15-C27 segment based on two types of stereospecific epoxide opening reactions

The C15-C27 segment of venturicidins was stereoselectively synthesized by using two types of stereospecific methyl substitution reactions of epoxides and subsequent stereocontrolled methylation reactions of lactone derivatives as the key steps.     

Profiling the metabolic differences of anthraquinone derivatives using liquid chromatography/tandem mass spectrometry with data‐dependent acquisition

This work concentrates on the in vitro metabolism of anthraquinone derivatives from rhubarb. Different metabolic reactions for anthraquinone derivatives were dependent on the substituent group in the skeleton. Monohydroxylation in the exocyclic methyl group was the major metabolic modification for emodin. Aloe‐emodin containing a hydroxymethyl group was mainly metabolized through a methylation reaction. For rhein, both hydrogenation and methyl substitution on the benzene ring were the major metabolic reactions. Hydroxyl substitution on the benzene ring was the predominant metabolic reaction for chrysophanol. For physcion, demethylation of the exocyclic methoxy group was the most important metabolic reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Pyridyl groups for protection of the imide functions of uridine and guanosine. Exploration of their displacement reactions for site-specific modifications of uracil and guanine bases

For the protection of the O-4 function of uridine and the O-6 of guanosine, 2-, 3- and 4-hydroxypyridines, 2-pyridinethiol, 6-methyl-2-hydroxy- and 6-methyl-3-hydroxypyridines have been employed. These substituted pyridines gave pyridyl-N-and/or pyridyl-O-substituted derivatives, depending both upon the position of the hydroxyl and methyl groups in the pyridine ring, at the C-4 and the C-6 of the uracil and guanine residues, respectively. These groups were found to be good leaving groups for nucleophilic substitution reactions by amines, thiolates and oximate. If needed, the rate of these substitution reactions could be conveniently increased by almost 1000-fold by conversion of the pyridyl moiety to its methiodide.     

Mapping the hydrolytic and synthetic selectivity of a type C feruloyl esterase (StFaeC) from Sporotrichum thermophile using alkyl ferulates

The active site of Sporotrichum thermophile type C feruloyl esterase (StFaeC) was probed using a series of C₁–C₄ alkyl ferulates. The affinities for straight and branched alkyl ferulates were demonstrated by the K_m values of 1.64–0.51 and 0.19–0.1, respectively. Comparison of k_cat and k_cat/K_m values shows that the enzyme hydrolyzed n-propyl ferulate faster and iso-propyl ferulate more efficiently. Alkyl ferulates were applied also for substrate selectivity mapping of feruloyl esterase to catalyze feruloyl group transfer to l-arabinose, using as a reaction system a ternary water–organic mixture consisting of n-hexane, t-butanol and water. Lengthening the aliphatic side chain was the most significant factor causing lower synthetic activity of the enzyme. The reaction parameters affecting the feruloylation rate and the conversion of the enzymatic process, such as the temperature and substrate concentration have been investigated. Under identical reaction conditions, the enzyme feruloylated other monosaccharides such as d-arabinose, d-glucose, d-xylose, d-mannose, d-fructose, d-galactose, d-ribose and model substrates such as 4-nitrophenyl α-l-arabinofuranoside and 4-nitrophenyl α-l-arabinopyranoside.     

C(3)-乙烯基的化学修饰与含氧基团取代的叶绿素-a衍生物的合成

以焦脱镁叶绿酸-a甲酯为起始原料, 通过加成和氧化反应将其3-位上的乙烯基转化为羟乙基、溴乙基、二羟乙基、二溴乙基和溴羟乙基, 再经过二甲亚砜/乙酸酐或者高钌酸四丙基铵(TPAP)/N-甲基吗啉-N-氧化物所组成的混合氧化剂的氧化反应, 得到多种C(3)-多酮基取代的二氢卟吩衍生物. 其单羟基作为离去基团与不同的活泼亚甲基化合物经过重排过程, 得到相应的酮基取代的二氢卟吩衍生物. 所得新叶绿素衍生物的化学结构均经UV, IR, ¹H NMR及元素分析得以证实, 并对相应的反应提出可能的反应机理.