Possible cage-like nanostructures formed by amino acids

We report possible cage-like nanostructures formed by a representative amino acid, serine octamers and decamers, determined by binding energy calculations and molecular dynamic simulations using the density functional tight-binding method. We used the l-handed serine to construct complex conformers linked by hydrogen bonds. We found the structures linked by -COOH···O=C- to be the most stable conformers and the calculation of the vibrational modes of complexes further illustrated this result. We attempted to apply our cage-like structures to the delivery of C(20) and cycloserine as model molecules. Our results may shed light on the design of cage-like biocompatible complexes for drug delivery.     

DFT study of structural, electronic, vibrational, and magnetic properties of the chirality cage-like molecule C24O12

Bonding, vibrational and magnetic properties of the cage-like molecule C(24)O(12) are studied by DFT calculations. Infrared- and Raman-active vibrational frequencies of the cage-like molecule C(24)O(12) are assigned. Two (13)C and one (17)O nuclear magnetic resonance (NMR) spectral signals of the cage-like molecule C(24)O(12) are characterized. Heat of formation of the cage-like molecule C(24)O(12) is estimated. Compared to C(60) and the cage-like molecule C(24)O(12), only from the thermodynamic points of view, C(24)O(12) is more stable than C(60). Thus we believe that the cage-like molecule C(24)O(12) has sufficient stability to allow its experimental preparation. We proposed that it could be synthesized by using the condensation of molecules C(6)(OH)(6) and C(12)Cl(12). Since the symmetry of C(24)O(12) is D(6), it is a chiral molecule.     

Gas-chromatographic determination of trace amino alcohols in water, air, and bitumen-salt masses forming in the detoxication of chemical warfare agents

A procedure was proposed for the determination of trace amino alcohols in various media using hydrochloric acid and acetic anhydride as gas-chromatographic derivatizing reagents. The developed procedures provide the determination of amino alcohols in water and air at a level of their maximum permissible concentrations (0.5 mg/L and 0.5 mg/m³, respectively) and in a bitumen-salt mass in a concentration of 5 x 10^-4%.     

Highly Chemoselective Aerobic Oxidation of Amino Alcohols into Amino Carbonyl Compounds

The direct oxidation of unprotected amino alcohols to their corresponding amino carbonyl compounds has often posed serious challenges in organic synthesis and has constrained chemists to adopting an indirect route, such as a protection/deprotection strategy, to attain their goal. Described herein is a highly chemoselective aerobic oxidation of unprotected amino alcohols to their amino carbonyl compounds in which 2‐azaadamantane N‐oxyl (AZADO)/copper catalysis is used. The catalytic system developed leads to the alcohol‐selective oxidation of various unprotected amino alcohols, carrying a primary, secondary, or tertiary amino group, in good to high yield at ambient temperature with exposure to air, thus offering flexibility in the synthesis of nitrogen‐containing compounds.     

Selective mono protection of diols, diamines, and amino alcohols using cesium bases

Efficient synthetic methods were developed for the synthesis of mono xanthates, as well as mono dithiocarbamates of diamines and amino alcohols. This protocol utilizes the three component coupling of diols, diamines, and amino alcohols using alkyl bromides and carbon disulfide in the presence of a cesium base and tetrabutylammonium iodide (TBAI).     

Chiral Ferrocenyl Amino Alcohols：Preparation and Application as Catalysts in the Enantioselective Reduction of Ketones Using NaBH4／I2

Five novel chiral ferrocenyl amino alcohols were prepared from natural amino acids and used as catalysts in the asymmetric reduction of prochiral ketones with NaBH4/I2 combination.The incorporation of the ferrocenyl moiety into the molecule of the chiral amino alcohols greatly improved their enantioselectivity in the catalysis.The optically active secondary alcohols were obt5ained in moderate to good enantiomeric excesses and high chemical yields.     

Selective One-Pot Conversion of Carboxylic Acids into Alcohols

Carboxylic acids are converted into alcohols by chemoselective reduction of their corresponding fluorides with sodium borohydride and dropwise addition of methanol. The method is general and mild and displays a high level of functional group compatibility. N-Protected amino and peptide alcohols, bearing varieties of protecting groups, are prepared in the same way from their corresponding amino acids and peptides without racemization.     

Enantiomeric differentiation of β‐amino alcohols under electrospray ionization mass spectrometric conditions

The enantiomeric differentiation of a series of chiral β‐amino alcohols (A) is attempted, for the first time, by applying the kinetic method using L‐proline, L‐tryptophan, 4‐iodo‐L‐phenylalanine or 3, 5‐diiodo‐L‐tyrosine as the chiral references (Ref) and Cu²⁺ or Ni²⁺ ion (M) as the central metal ion. The trimeric diastereomeric adduct ions, [M+(Ref)₂+A‐H]⁺, formed under electrospray ionization conditions, are subjected for collision‐induced dissociation (CID) experiments. The products ions, formed by the loss of either a reference or an analyte, detected in the CID spectra are evaluated for the enantiomeric differentiation. All the references showed enantiomeric differentiation and the R_chiral values are better for the aromatic alcohols than for aliphatic alcohols. Notably, the R_chiral values of the aliphatic amino alcohols enhanced when Ni²⁺ is used as the central metal ion. The experimental results are well supported by computational studies carried out on the diastereomeric dimeric complexes. The computational data of amino alcohols is correlated with that of amino acids to understand the structural interaction of amino alcohols with reference molecule and central metal ion and their role on the stabilization of the dimeric complexes. Application of flow injection MS/MS method is also demonstrated for the enantiomeric differentiation of the amino alcohols. Copyright © 2014 John Wiley & Sons, Ltd.     

Convenient synthesis of stable aldimine-borane complexes, chiral delta-amino alcohols, and gamma-substituted GABA analogues from nitriles

A one-pot synthesis of stable aldimine-trialkylborane adducts, the first synthesis of C- and N-deuterated imine-borane complexes, and their application for a highly enantioselective (84-99% ee) synthesis of delta-amino alcohols and gamma-substituted gamma-aminobutyric acids, including deuterated amino acids from nitriles, are described.     

Specific recognition of chiral amino alcohols via lanthanide coordination chemistry: structural optimization of lanthanide tris(beta-diketonates) toward effective circular dichroism/fluorescence probing

Lanthanide tris(beta-diketonates) formed stable, 1:1 highly coordinated complexes with amino alcohols, and the resulting complexes exhibited large enhanced fluorescence and intense induced circular dichroism (CD) signals. The stability constants of the highly coordinated complexes were determined for various combinations of lanthanide centers, beta-diketonate ligands, and organic substrates. These revealed that amino alcohol coordinated with the lanthanide center much more strongly than monoamine, monoalcohol, or diol derivative. On the basis of the highly coordinated complexation, several lanthanide tris(beta-diketonates) acted as CD/fluorescence probes specific for amino alcohols. Tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octadionato)europium(III) showed enhanced fluorescence in the presence of amino alcohols, while the corresponding ytterbium complex exhibited chirality-dependent CD signals for amino alcohols. In particular, the observed CD spectral profiles related well with the absolute configuration and optical purity of the bound amino alcohol, indicating that the structural optimization of lanthanide tris(beta-diketonates) offered specific sensing of amino alcohols and precise determination of their enantiomer excess percentages.     

Amino alcohols as ligands for nickel-catalyzed suzuki reactions of unactivated alkyl halides, including secondary alkyl chlorides, with arylboronic acids

Suzuki cross-coupling reactions of an unprecedented array of unactivated primary and secondary alkyl halides (including challenging alkyl chlorides) can be accomplished through the use of nickel/amino alcohol-based catalysts. Both the nickel precatalyst and the amino alcohols (prolinol or trans-2-aminocyclohexanol) are commercially available and air-stable. In view of the remarkable diversity of amino alcohols that are readily accessible, this discovery may open the door to the rapid development of versatile catalysts for a wide range of cross-coupling processes.     

Influence of additives on the clouding phenomenon of chlorpromazine hydrochloride solutions

Herein we report the effect of various additives (viz. alcohols, cycloalcohols, amino acids, sugars, ureas) on the clouding phenomenon observed in 50mM chlorpromazine hydrochloride (CPZ) drug solutions (prepared in 10mM sodium phosphate buffer). Long chain alcohols (except octanol), cyclohexanol and allylalcohol increased the cloud point (CP) followed by a decrease with the increase in alcohol concentration but short chain alcohols affected the CP insignificantly. Effect of amino acids depended upon their nature: acidic and salts of basic amino acids increased the CP while basic amino acids depressed it; non-polar and uncharged polar amino acids caused small changes in CP. Additives of urea family decreased the CP. All sugars caused a decrease in CP, which is in consonance to their effect on the critical micellar concentration. The overall behavior is explained on the basis of additives affecting the solvent as well as micelle aggregation and/or structure.     

Prediction of retention indexes. III. Silylated derivatives of polar compounds.

Polar compounds containing hydroxyl, amino and carboxyl groups, singly or in combination, can be chromatographed after the polar functional groups are silylated. The silylated derivatives of acids, alcohols, amines, diols, amino alcohols, amino acids are shown to behave chromatographically as hydrocarbons, and their retention indexes can be readily predicted from their base values. The column difference, namely, the difference between the retention indexes of the analyte on polar and non-polar columns is minimal for the silylated derivatives in comparison to that observed for the underivatized analytes. This minimal column difference is attributed to the hydrocarbon-like chromatographic characteristics of the silylated derivatives. The retention indexes of the silyl derivatives appear to correlate with the atom number Z of the analyte.     

手性氨基酸及其衍生物配体在酮不对称氢转移反应中的应用进展

前手性酮的不对称氢转移反应(ATH)是获得手性醇的重要方法.近年来氨基酸及其衍生物在金属Ru,Rh,Ir催化酮的ATH中的应用引起人们关注.就氨基酸、氨基酸酰胺、氨基酸硫代酰胺、氨基酸羟胺酸、氨基酸酰肼、氨基醇及氨基酸羟基酰胺等为配体的金属络合物在ATH中的催化性能进行了综述.     

Free Amino Acids and Volatile Aroma Compounds in Watermelon Rind,Flesh, and Three Rind-Flesh Juices

Watermelon rind is treated as agricultural waste, causing biomass loss and environmental issues. This study aimed to identify free amino acids and volatiles in watermelon rind, flesh, and rind-flesh juice blends with ratios of 10%, 20%, and 30%. Among the 16 free amino acids quantified, watermelon rind alone contained higher total amino acids (165 mg/100 g fresh weight) compared to flesh alone (146 mg/100 g). The rind had significantly higher (1.5×) and dominant amounts of citrulline and arginine (61.4 and 53.8 mg/100 g, respectively) than flesh. The rind, however, contained significantly lower amounts of essential amino acids. Volatile analysis showed that watermelon rind total volatiles (peak area) comprised only 15% of the flesh volatiles. Of the 126 volatiles identified, the rind alone contained 77 compounds; 56 of these presented in all five samples. Aldehydes and alcohols were most prevalent, accounting for >80% of the total volatiles in all samples. Nine-carbon aldehyde and alcohol compounds dominated both the flesh and rind, though the rind lacked the diversity of other aldehydes, alcohols, ketones, terpenes, terpenoids, esters and lactones that were more abundant in the watermelon flesh. Watermelon rind was characterized by the major aroma compounds above their thresholds, including 17 aldehydes and six unsaturated nine-carbon alcohols. This study demonstrated the potential for rind as a food or beverage supplement due to its key features such as concentrated citrulline and arginine, relatively low odor intensity, and valuable volatiles associated with fresh, green, cucumber-like aromas.     

Enantiomeric impurities in chiral synthons,catalysts, and auxiliaries: Part 3

The enantiomeric excess of chiral reagents used in asymmetric syntheses directly affects the reaction selectivity and product purity. In this work, 84 of the more recently available chiral compounds were evaluated to determine their actual enantiomeric composition. These compounds are widely used in asymmetric syntheses as chiral synthons, catalysts, and auxiliaries. These include chiral alcohols, amines, amino alcohols, amides, carboxylic acids, epoxides, esters, ketones, and oxolanes among other classes of compounds. All enantiomeric test results were categorized within five impurity levels (i.e., <0.01%, 0.01–0.1%, 0.1–1%, 1–10%, and >10%). The majority of the reagents tested were determined to have enantiomeric impurities over 0.01%, and two of them were found to contain enantiomeric impurities exceeding the 10% level. The most effective enantioselective analysis method was a GC approach using a Chiraldex GTA chiral stationary phase (CSP). This method worked exceedingly well with chiral amines and alcohols.     

咪唑(啉)-2-羧酸盐作为潜在的/可热活化的有机小分子催化剂催化转酯反应(英文)

采用咪唑(啉)-2-羧酸盐(ImCO2)作为催化剂前驱体,通过温度控制脱除ImCO2的2-位羧酸根,再原位释放出高活性的N-杂环卡宾(NHCs),进而催化转酯反应.研究了NHCs在苯甲酸乙酯与一元醇、二元醇及氨基醇反应体系中的催化活性.结果表明,在该体系中不需要选用活化酯为原料,无需加入分子筛或加大醇酯比提高产率,仅用少量催化剂(0.5mol%),在较短时间内(3h),即可使反应转化率达到95%.     

Asymmetric synthesis of highly substituted beta-nitro alcohols and enantiomerically enriched 4,4,5-trisubstituted oxazolidinones

It is demonstrated that alpha,alpha-disubstituted-alpha-nitroketones are reduced to the corresponding trisubstituted nitro alcohols in good to excellent yield and enantiomeric excess by borane-dimethyl sulfide in the presence of a chiral oxazaborolidine catalyst. Reduction of the nitro alcohols to the corresponding amino alcohols and their subsequent conversion to enantiomerically enriched 4,4,5-trisubstituted oxazoldinones is also reported.     

Ketones of the 1, 4-benzodioxane series

New amino ketones and amino alcohols of the 1, 4-benzodioxane series, of pharmacological interest, are synthesized.For Part VII see [1].     

Synthesis of noval chiral tridentate amino alcohols as chiral solvating agents under ball-milling conditions

A new family of chiral solvating agents based on chiral didentate amino alcohols and chloromethyl pyridine derivatives were synthesized by ball milling in solvent free condition. The new chiral tridentate amino alcohols were tested as chiral NMR solvating agents for the Ts-derivatives of amino acids, other several acids and pyrazole drugs. For the Ts-derivatives of amino acids studied herein, chiral tridentate amino alcohol 3a could be used for the assignment of the absolute configurations of their racemes through the chemical shift non-equivalences of their CH₃ (Ts) protons with certain confidence.