Highly enantioselective aryl transfer to aldehydes: a remarkable effect of sulfur substitution in amino thioacetate ligands

Chiral amino thioacetate ligands were prepared from the corresponding amino alcohols and used as catalysts for enantioselective aryl transfer reaction. The amino thioacetates were remarkably superior to the corresponding amino alcohols. Low catalyst loadings of only 1-2.5 mol % were sufficient to achieve excellent enantioselectivity as well as high conversion in short reaction time. The results reveal that the thioacetoxy moiety of the amino thioacetates has a surprisingly beneficial effect in enhancing the asymmetric induction.     

"Click chemistry" inspired synthesis of pseudo-oligosaccharides and amino acid glycoconjugates

[reaction: see text] Various pseudo-oligosacchardies and amino acid glycoconjugates were synthesized via an intermolecular 1,3-dipolar cycloaddition ("click") reaction using easily accessible carbohydrate and amino acid derived azides and alkynes as building blocks. It is pertinent to mention that the conjugation reaction is highly regioselective and high yielding and can be carried out under mild reaction conditions.     

Study on Production of Amino Acids from Bean Dregs by Hydrolysis in Sub-critical Water

This study investigated the production of value‐added amino acids from bean dregs by hydrolysis in subcritical water. It was investigated that the effect of reaction temperature, reaction time and CO₂ on amino acid concentration in the hydrolysates of bean dregs. The product of amino acid was determined by Amino Acid Analyzer. The results show that a variety of amino acids are produced. The concentrations of arginine, lysine and alanine were relatively high in the hydrolysate. Temperature and time have a great influence on the hydrolysis reaction. The effects of reaction temperature and time on concentration of different amino acids vary. The addition of carbon dioxide led to an increase in amino acid yield due to the acceleration of acid hydrolyzed catalysis steps. The highest yield of total amino acids is 22% (0.22 g/g of dry bean dregs) at 330°C and 30 min. This method may provide a practical and economical solution for the disposal of bean dregs wastes.     

Organocatalytic Formation of Chiral Trisubstituted Allenes and Chiral Furan Derivatives

A novel reaction that provides chiral allenes by amino catalytic activation of either aldehydes or α,β‐unsaturated aldehydes for reaction with alkynyl‐substituted enones is presented. The reaction forms a variety of trisubstituted allenes in high yields and with excellent stereoselectivities. The utility of the reaction concept is demonstrated by the synthesis of chiral furan derivatives in high yields and stereoselectivities.     

Acyclic chiral amines and amino acids as inexpensive and readily tunable catalysts for the direct asymmetric three-component Mannich reaction

The direct three-component asymmetric Mannich reaction catalyzed by acyclic chiral amines or amino acids is presented. Simple acyclic chiral amines and amino acids--such as alanine-tetrazole (9), alanine, valine, and serine-catalyzed the three-component asymmetric Mannich reactions between unmodified ketones, p-anisidine, and aldehydes with high chemo- and stereoselectivity, furnishing the corresponding Mannich bases with up to >99 % ee. This study demonstrates that the whole range of amino acids in nature, as well as nonproteogenic amino acid derivatives, can be considered in the design and tuning of novel, inexpensive organocatalysts for the direct asymmetric Mannich reaction.     

QUALITATIVE UNTERSUCHUNGEN ZUR PHOTOLYSE EINFACHER DIPEPTIDE

Abstract— The photolyses of eight chromatographical pure dipeptides were studied. They were irradiated by the total spectrum of a high pressure mercury lamp. The resulting products were separated by electrophoresis and identified by paper chromatography. It was found that the carbonyl group of the N-terminal amino acid was eliminated in a dipeptide; an amine and an amino acid were found as primary products. This reaction is accompanied by a second reaction, the decarboxylation of the C-terminal amino acid. Possible mechanisms of these reactions are discussed.     

Enantioselective decarboxylation of beta-keto esters with Pd/amino alcohol systems: successive metal catalysis and organocatalysis

The kinetics and mechanisms of one-pot cascade reactions of racemic beta-keto esters to give chiral ketones in the presence of Pd/C-chiral amino alcohol catalyst systems were studied. Transformation of 2-methyl-1-tetralone-2-carboxylic acid benzyl ester (1) into 2-methyl-1-tetralone (4) in the presence of Pd/C and cinchona alkaloids or ephedrine was chosen as a model reaction. After the first reaction step, the Pd-catalysed debenzylation of 1 to afford the corresponding beta-keto acid (2), there are two possible reaction routes that may be catalysed by the chiral amino alcohol in solution or by Pd(0) sites on the metal surface in cooperation with the adsorbed amino alcohol. The reaction intermediate 2 was synthesized, and the kinetics of decarboxylation were followed by NMR, UV and IR spectroscopy. The studies revealed that the role of Pd is to trigger the reaction series by deprotection of 1. The subsequent dominant reaction route from the racemic beta-keto acid 2 to the chiral ketone 4 is catalysed by the chiral amino alcohol in the liquid phase. It is shown that kinetic resolution of the diastereomeric salt of rac-2 and the chiral amino alcohol plays a key role in the enantioselection. High enantioselectivity necessitates an amino alcohol/rac-2 ratio of at least 2. A high ratio favours the formation of 1:1 amino alcohol/acid diastereomeric complexes, and the second amino alcohol molecule may be responsible for the enantioselective protonation of 2 in the diastereomeric complex.     

Hydroxylation of aromatic rings in an aqueous solution induced by argon arc plasma

Plasma-induced reaction in an aqueous solution of phenyl-containing amino acids resulted in the formation of several hydroxyphenyl amino acids, which was explained by the action of hydroxyl radicals generated by decomposition of water molecules by the high energy plasma.     

Selective reaction of amino acid sulfoximines with nitrous acid; facile stereospecific conversion to amino acid sulfoxides

N-Unsubstituted sulfoximines of amino acids can he readily converted to the corresponding amino acid sulfoxides in high yields by treatment with stoichiometric quantities of nitrous acid. Under the conditions employed, reaction with L-methionine-S (or R)-sulfoximine is specific for the sulfoximine nitrogen atom, and no reaction occurs at the α-amino group. Conversion to the sulfoxide proceeds with complete retention of configuration at the sulfur atom.     

高效和可重复使用的Zr-MCM-41催化剂催化Strecker反应合成氨基腈类化合物(英文)

The synthesis and characterization of Zr-MCM-41 nanoreactors and their catalytic activity in the synthesis of new amino nitrile derivatives by the Strecker reaction in high yields and in short reaction times is reported.     

Effect of basic amino acids on photoreaction of ketoprofen in phosphate buffer solution

Photoreaction of ketoprofen (KP), one of the widely used nonsteroidal anti-inflammatory drugs (NSAIDs), was studied with transient absorption spectroscopy in phosphate buffer solution (pH 7.4) in the presence of basic amino acids of histidine (His), lysine (Lys) and arginine (Arg). Deprotonated form of KP (KP(-)) excited with UV-light irradiation gave rise to carbanion through a decarboxylation reaction. It was found that carbanion abstracted a proton from the side chain of the protonated amino acids to yield 3-ethylbenzophenone ketyl biradical (EBPH); however, no reaction was observed with alanine. The relative yield of EBPH by the proton transfer reaction with His was ca. 40 times larger than that of the other two basic amino acids, suggesting that the proton-donating ability of His (protonated His) should be quite high. The information on the photoreaction mechanism of NSAIDs with basic amino acids was essential to understand primary reaction of excited NSAIDs in vivo causing photosensitization on human skin.     

An efficient synthesis of γ-amino β-ketoester by cross-Claisen condensation with α-amino acid derivatives

Cross-ester condensation between N-protected amino acid ester and the lithium enolate prepared from alkyl acetate gave the corresponding β-ketoester in high yield without the formation of the tertiary alcohol that is commonly seen as by-product. This interesting reaction is applicable to the amino acid derivatives with suitable N-protecting groups, which can help to stabilize the reaction intermediates.     

Utilizing the high dielectric constant of water: efficient synthesis of amino acid-derivatized cyclobutenones

This work reports the use of water as a solvent to facilitate an efficient syntheses of amino acid-derivatized cyclobutenone. Kinetics studies in different solvents reveals that high dielectric constants of the solvents are the primary attribute for the high yielding and fast rate for this reaction. This class of substitution reactions in water also proceeds efficiently with a wide range of amino acids.     

Transforming natural amino acids into alpha-alkyl-substituted amino acids with the help of the HOF.CH3CN complex

Alpha-alkyl amino acids can be efficiently prepared in high yields from the respective amino acids themselves. The key step is the oxidation of the amine function to create the corresponding alpha-nitro acid in a fast and very high yield reaction followed by phase-transfer alkylation and finally reduction to the desired alpha-alkyl amino acid. Several such acids containing aromatic rings or additional carboxylic groups and acids with steric hindrance at the alpha-position are suitable substrates. Several alkyl halides were examined as alkylating agents.     

Chemoselective peptide bond formation using formyl-substituted nitrophenylthio ester

A novel method for peptide bond formation utilizing amino acid 2-formyl-4-nitrophenylthio ester has been developed. The reaction can be performed in water-containing media and is compatible with various types of amino acid side-chain functional groups. Use of N-methylmaleinimide as an additive is essential for the reaction to proceed with high efficiency. It captures liberated formyl-substituted thiophenol through 1,4-addition followed by aldol cyclization.     

Rapid synthesis of highly functionalised α-amino amides and medium ring lactones using multicomponent reactions of amino alcohols and isocyanides

Four-component reactions between amino alcohols, aldehydes, isocyanides and thiols proceed rapidly under microwave or conventional heating at 60 °C in methanol. The reaction is successful with a wide range of components and gives access to potentially drug-like products containing amine, amide and thioether functionality in moderate to excellent yield. The reaction conditions are also applicable to the synthesis of a range of 8-10 membered medium ring lactones via three-component reactions of amino alcohols, isocyanides and acid-aldehydes. Incorporation of L-prolinol as the amino alcohol component in each case gives access to multicomponent products with moderate to high diastereoselectivity.     

Synthesis of Chiral Benzimidazoles as Acylating Agents for Kinetic Resolution of Racemic α‐Amino Esters

A series of novel chiral 1‐benzoyl‐2‐(α‐N‐substituted aminoethyl)benzimidazoles are synthesized with the improved method in high yields (72–84%) and developed as nonenzymatic acylating agents for kinetic resolution of racemic α‐amino esters. The process exhibits high enantioselectivity (ee up to 94%) for α‐amino esters under mild reaction conditions.     

Gold-catalyzed multicomponent synthesis of aminoindolizines from aldehydes, amines, and alkynes under solvent-free conditions or in water

A gold(III)-catalyzed multicomponent coupling/cycloisomerization reaction of heteroaryl aldehydes, amines, and alkynes under solvent-free conditions or in water has been developed. This methodology provides rapid access to substituted aminoindolizines with high atom economy and high catalytic efficiency. Especially, the coupling of enantiomerically enriched amino acid derivatives produces the corresponding N-indolizine-incorporated amino acid derivatives without loss of enantiomeric purity.     

Diastereo‐ and Enantioselective Palladium‐Catalyzed Dearomative [3+2] Cycloaddition of 3‐Nitroindoles

Diastereo‐ and enantioselective cycloaddition of 3‐nitroindoles with vinyl aziridine was realized under Pd‐catalysis using commercially available Walphos as the ligand, affording pyrroloindolines in high yields with high diastereo‐ and enantioselectivities. The reaction can be scaled up to a gram scale and the reaction products are easily converted to amino pyrroloindoline and other pyrroloindoline derivatives.     

Transient silylation of the guanosine O6 and amino groups facilitates N-acylation

[reaction: see text] The formation of a guanosine derivative silylated at both the O6 and amino groups was identified by (15)N NMR. This intermediate allows facile reaction with acetyl chloride or phenoxyacetyl chloride to give in high yield the corresponding N-protected guanosine derivatives, suitable for use in RNA synthesis. The acetyl and phenoxyacetyl amino protecting groups are, respectively, 4 and 230 times more labile than the isobutyryl group to methylamine/ethanol deprotection.