Primary Amine‐Initiated Polymerizations of α–Amino Acid N‐Thiocarbonic Acid Anhydrosulfide

The N‐thiocarbonic acid anhydrosulfides NTAs of D,L‐leucine, D,L‐phenylalanine and sarcosine were polymerized in dioxane by addition of n‐hexylamine as initiator. Despite variation of the monomer‐initiator ratio (M/I) only low yields of oligopeptides were obtained from D,L‐Leu‐ and D,L‐Phe‐NTA. Both yields and molecular weights were almost twice as high for polymerizations of Sar‐NTA. MALDI‐TOF mass spectra confirmed that the isolated oligo‐and polypeptides possess the expected structure with one reactive amino end group. Therefore, it is surprising that the polymerizations stopped at low conversions. Two hypotheses explaining this phenomenon are discussed.     

Antibacterial activity of cyclo(L-Pro-L-Tyr) and cyclo(D-Pro-L-Tyr) from Streptomyces sp. strain 22-4 against phytopathogenic bacteria

Two bioactive cyclic dipeptides, cyclo(L-Pro-L-Tyr) and cyclo(D-Pro-L-Tyr), were isolated from the culture broth of Streptomyces sp. strain 22-4 and tested against three economically important plant pathogens, Xanthomonas axonopodis pv. citri, Ralstonia solanacearum and Clavibacter michiganensis. Both cyclic dipeptides were active against X. axonopodis pv. citri and R. Solanacearum with MIC of 31.25 μg/mL. No activity could be observed against C. michiganensis.     

The Structure of N‐(1‐Deoxy‐β‐D‐fructopyranos‐1‐yl)‐L‐proline Monohydrate (“D‐Fructose‐L‐proline”) and N‐(1,6‐Dideoxy‐α‐L‐fructofuranos‐1‐yl)‐L‐proline (“L‐Rhamnulose‐L‐proline”)

Nano n-propylsulfonated γ-Fe₂O₃ was found to be a highly efficient, reusable heterogeneous catalyst for the conversion of a range of monosaccharides and some of their derivatives to the corresponding O-isopropylidene derivatives in good to excellent yields by refluxing the reaction mixture in dry acetone. The magnetic property of the catalyst enabled its separation from the reaction mixture by a simple process of filtration along with the aid of an external magnet. The efficiency of the catalyst was found to be largely unaffected for at least up to six cycles of reuse, thus proving the new methodology to be environmentally rewarding besides being simple and facile in operation.     

Synthesis of L‐6‐Chloropyrroloindoline of Chloptosin Cyclohexapeptide

Abstract

Chloptosin is an apoptosis‐inducing dimeric cyclohexapeptide. Enantioselective synthesis of L‐6‐chloropyrroloindoline, as the key chiral synthon of the cyclohexapeptide of chloptosin, was successfully achieved starting from 3‐chloroaniline by utilizing Fischer indole/Schöllkopf protocol and oxidative cyclization of resulting L‐6‐chlorotryptophan.     

Thermo-sensitive random poly(L-alanine-co-L-lactic acid) with no cytotoxicity by the structure-controlled synthesis for a nano-drug carrier

A random poly(L-alanine-co-L-lactic acid) (PAL) with excellent thermo-sensitivity and no cytotoxicity was synthesized by the structure-controlled polycondensation from natural L-alanine and L-lactic acid. Only those PALs in which the contents of L-alanine structural unit are rigidly controlled in the smaller range of 53–65% show a reversible lower critical solution temperature of 35–60°C. The change of secondary structure in poly(L-alanine) segments by the introduction of L-lactic acid structural unit plays a decisive role in regulating the thermo-sensitivity of PAL. The viability of HeLa cells exposed to PAL reaches up to 91–116% after incubation of 24 and 72?h, indicating no cytotoxicity. Furthermore, PAL can easily form curcumin-loaded nano-carriers through its thermo-sensitivity and self-assembly. The curcumin-loaded PAL nano-particles are observed to clearly internalize into the cells by confocal laser-scanning microscopy, and thus can be used as a potential nano-drug-carrier.     

Complex formation of curium(III) with amino acids of different functionalities: L-threonine and O -phospho-L-threonine

The speciation of curium(III) with L-threonine and O-phospho-L-threonine was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3?×?10^?7?M). Curium species of the type M_pH_qL_r were identified in the L-threonine- and O-phospho-L-threonine system. These complexes are characterized by their individual luminescence spectra and luminescence lifetimes. The following formation constants were determined (a) for L-threonine: log?β₁₀₁?=?6.72?±?0.07, log?β₁₀₂?=?10.22?±?0.09, and log?β_1–22?=?(7.22?±?0.19) at ionic strength I?=?0.5?M and (b) for O-phospho-L-threonine: log?β₁₂₁?=?18.03?±?0.13 and log?β₁₁₁?=?14.17?±?0.09 at ionic strength I?=?0.154?M. Possible structures of the identified curium species are discussed on the basis of the luminescence lifetime measurements and the magnitude of the formation constants.     

Synthesis,characterization and crystal structures of two binary acid complexes based on L-glutamate and L-aspartate

Two amino acid complexes, [Cd(L-glu)(H₂O)] _n ?·?nH₂O (1) and [Co(L-asp)(phen)(N₃)]?·?2H₂O (2) (L-glu?=?L-glutamate, L-asp?=?L-aspartate, phen?=?1,10-phenanthroline), have been synthesized and characterized by elemental analyses, IR spectra and TG-DSC analysis. Single crystal X-ray structure analyses revealed that each L-glutamate acts as a pentadentate ligand binding to three octahedral Cd(II) atoms through the amino group and two carboxyl groups to form a neutral helical network. Complex 2 is a mononuclear compound in which Co(III) is octahedrally coordinated by tridentate L-aspartate, monodentate azide and chelating phen ligand. Thermal stability and fluorescence of 1 have been investigated. The complex shows strong blue fluorescence in the solid state.     

Studies on the Conformation of Polyhydroxyalkylpyrazolo (3,4-b) Quinoxalines

¹H NMR spectral studies on polyhydroxyalkylpyrazolo-(3,4-b)-quinoxaline derivatives of sugars having five to seven carbon atoms have shown that the polyhydroxyalkyl chain exists in a conformation in which a hydrogen bond is formed between the l'-hydroxyl group and N-2 of the pyrazolo(3,4-b)-quinoxaline base moiety. The polyhydroxyalkyl chain exists in the planar zigzag conformation, where no 1,3 syn axial interaction is present. Substitution in the base moiety did not change the extent of the population of the planar zigzag conformation.     

Enantioselective,Potentiometric Membrane Electrodes Based on Cyclodextrins for the Assay of L‐ and D‐2‐Hydroxyglutaric Acid

Abstract

Enantioselective, potentiometric membrane electrodes (EPMEs) based on immobilization of β‐, γ‐cyclodextrin (CD) or 2‐hydroxy‐3‐trimethylammoniopropyl‐β‐cyclodextrin (as chloride salt) (β‐CD‐derivative) in carbon paste have been designed. The β‐CD and β‐CD‐derivative‐based electrodes were applied in the 10^?8–10^?6 and 10^?7–10^?5 mol/L concentration ranges for the determination of L‐2‐hydroxyglutaric acid (L‐2‐HGA), whereas γ‐CD‐based electrode was applied for the determination of D‐2‐hydroxyglutaric acid (D‐2‐HGA) in the concentration range 10^?6–10^?4 mol/L. The β‐CD‐based EPME showed the lowest detection limit (1×10^?9 mol/L). The enantioselectivity and selectivity of the proposed electrodes for the assay of L‐2‐HGA and D‐2‐HGA, respectively, were determined over D‐2‐HGA/L‐2‐HGA, creatine, and creatinine. The proposed EPMEs can be applied for the enantioanalysis of 2‐hydroxyglutaric acid in urine samples.     

Amphiphilic Networks. I. Network Synthesis by Copolymerization of Methacryloyl-Capped Polyisobutylene with 2-(Dimethylamino) Ethyl Methacrylate and Characterization of The Networks

New amphiphilic networks have been synthesized by free-radical co-polymerization of hydrophobic methacryloyl-capped polyisobutylenes (MA-PIB-MA) with hydrophilic 2-(dimethylamino)ethyl methacrylate. Two MA-PIB-MAs have been prepared with M_n = 4920 and 10 200, and two series of networks were prepared with MA-PIB-MA contents between 48 and 71.5%. Variation of the molecular weight of MA-PIB-MA and its concentration in the network allows for a wide range of mechanical properties and swellability in hydrophilic and hydrophobic solvents. Differential scanning calorimetry shows the existence of two glass transitions in these networks and thus indicates a phase-separated domain structure. Tensile strengths and elongations were dependent on MA-PIB-MA contents varying from 57.7 to 39.8 kg/cm² and from 168 to 200%, respectively, with increasing MA-PIB-MA content. Solvent swelling of the networks ranged from 170 to 20% in water and from 40 to 170% in n-heptane with increasing MA-PIB-MA contents.     

Syntheses and crystal structures of cis - and trans -copper(II) complexes of L-arginine

Two copper(II) complexes of L-arginine, trans-[Cu(l-Arg)₂(NO₃)]NO₃ · 3H₂O (1) and {cis-[Cu(l-Arg)₂](NO₃)₂ · 3H₂O} _n (2) (Arg = arginine) were prepared by reaction of Cu(NO₃)₂ · 3H₂O and L-arginine in acetone and aqueous solution, respectively. X-ray analysis reveals 1 crystallizes in a monoclinic system, P2₁ with a = 10.3857(15), b = 16.885(3), c = 15.9586(19) Å, β = 15.9586(19)°, Z = 4, V = 2654.2(6) ų. The copper(II) centers lie in a distorted N₂O₃ square-pyramidal environment. While 1 adopts a mononuclear structure, and the axial position occupied by a nitrate with Cu1–O9 = 2.535 Å and Cu2–O20 = 2.581 Å, 2 features a 1-D infinite chain structure. In 1, adjacent monomeric units connect with each other to give a 2-D layer structure of (4, 4) nets through hydrogen bonds between the guanidinium and carboxylic groups of arginine, and 2-D layers further assemble to a 3-D supermolecular structure via a series of inter-layer hydrogen bonds.     

Syntheses and characterizations of zinc(II) and copper(II) complexes with reduced Schiff base derived from salicylaldehyde and D,L-selenomethionine

New zinc(II) and copper(II) complexes with a reduced Schiff-base ligand derived from D,L-selenomethionine and salicylaldehyde have been synthesized and characterized by elemental analysis, magnetic susceptibility, IR, and NMR measurements. The single-crystal X-ray structure of the Cu(II) complex reveals that this complex is a carboxylate-bridged dimer of dinuclear copper(II) subunits and all metal centers are five-coordinate with O₄N donor sets in distorted square-pyramidal geometries. The Cu(II) complex consists of a 1-D coordination polymer.     

Thermal Properties of Copoly(L‐lactic acid/glycolic acid) by Direct Melt Polycondensation

Poly(L‐lactic acid‐co‐glycolic acid) (PLGA) was prepared from hydroxy‐acids with melt polymerization. In this way, the copoly(L‐LA/GA) (PLGA) was synthesized directly using a binary catalyst (tin chloride dihydrate/p‐toluenesulfonic acid). The thermal properties of PLGA were studied by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR). The results show that the melting point of PLGA decreases with increasing mole fraction of GA units in the copolymer. In addition, the melting point of polymer also decreases with increasing degree of racemization of the polymer.     

Long‐Term Stabilization of the Activity of Ascorbate Oxidase Adsorbed on a Porous Carbon Material by Polymaleimidostyrene

Abstract

The biological catalysts adsorbed on the carbon surface gradually lost their activities. In order to prolong stabilization of the enzyme activity, polymaleimidostyrene (PMS) was used to preserve enzyme conformation. Sulfhydryl and amino groups of enzyme or biological tissue can be covalently bound to PMS. By using the carbon material coated by PMS, the stability of L‐ascorbic acid sensor response using purified enzyme was significantly improved, and its initial response was not decreased at all for 150 days, although the purified enzymes adsorbed to the carbon without PMS lost their activity 22.5% after 10 days.     

CuI/L-Proline-Catalyzed Synthesis of Vinyl Sulfides in 95% Alcohol

A method for the synthesis of vinyl sulfides using the simple CuI/L-proline as a catalyst system is reported. The best yields were obtained in the 95% ethanol with 10 mol% CuI, 20 mol% L-proline, and 1.2 equiv of K₂CO₃. The amino acids act as base and excellent promoter for the copper-catalyzed coupling reactions, and this protocol tolerates both aromatic and heterocyclic thiols and avoids using other expensive additives.     

Synthesis of Protected Hydroxyethylamine Transition-State Analogs of N-Ac-Muramyl-L-alanine

A novel N-acetyl-α-D-glucosamine derivative containing an epoxide moiety 5 has been synthesized and converted into a series of protected hydroxyethylamine transition-state analogs of N-Ac-muramyl-L-ala peptide 6a–e using a microwave-accelerated reaction.     

Electrochemical and Electrocatalytic Properties of Ferrocene Incorporated in L‐Cysteine Self‐Assembled Monolayers on a Gold Electrode

Abstract

The preparation of a gold electrode modified by aminylferrocene (FcAI) covalently bound to L‐cysteine self‐assembled monolayer (L‐Cys/Au SAM) was described, and characterized by cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS). In pH 7.4 buffers, FcAI incorporated in L‐Cys/Au SAM gave a pair of well‐defined and quasi‐reversible cyclic voltammetric peaks at 0.109 vs. saturated calomel eletrode (SCE), characteristic of Fe(II)/Fe(III) redox couples of the Fc. The apparent surface electron transfer rate constant is 6.86 s^?1 at the modified electrode. The immobilized Fc gave an excellent electrocatalytic activity for the oxidation of epinephrine (EP). The catalytic current of EP vs. its concentration has a good linear relation in the range of 1.7×10^?7–1.0×10^?4 mol/L, with the correlation coefficient of 0.9975 and detection limit of 1.8×10^?8 mol/L. The modified electrode can be used for the determination of EP in practical injection. The method is simple, quick, sensitive, and accurate.     

Concise and Efficient Synthesis of Highly Potent and Selective Dipeptidyl Peptidase II Inhibitors

Highly potent and selective DPP II inhibitors N′‐(4‐Chlorobenzyl)‐N′‐methyl‐4‐oxo‐4‐(1‐piperidinyl)‐1,3‐(S)‐butane‐diamine dihydrochloride 1 and N′‐(4‐chlorobenzyl)‐4‐oxo‐4‐(1‐piperidinyl)‐1,3‐(S)‐butanediamine dihydrochloride 2 have been efficiently synthesized starting from L‐glutamine. A short and high yielding route with simple isolation techniques has been disclosed.     

L ‐Proline‐Promoted CuI‐Catalyzed C‐S Bond Formation between Aryl Iodides and Thiols

An improved, mild procedure for the CuI‐catalyzed coupling reactions of aryl iodides with aliphatic and aromatic thiols, using L ‐proline as the ligand, is reported. This procedure is noteworthy given its high generality and exceptional level of functional group toleration.     

Synthesis of metal-organic frameworks from the system metal/L-glutamic acid/TEA/H2O

Three metal-organic frameworks (MOFs) with similar zeolite-like 3-D structures, Zn(L-Glu)(H₂O) · H₂O, Cu(L-Glu)(H₂O) · H₂O, and Co(L-Glu)(H₂O) · H₂O, have been obtained from metal/L-glutamic acid/TEA/H₂O systems, whereby the weak base triethylamine (TEA), rather than the more typically used NaOH or Na₂CO₃, has been used to adjust the pH of the solution. A systematic and detailed exploration of the synthesis conditions has revealed that not all transition metals may be coordinated to L-glutamic acid and that the range of conditions under which the three MOFs remained stable was different. The metal/L-glutamic acid/TEA/H₂O system offers an effective means of obtaining MOFs.