Synthesis of a boronated amino acid as a potential neutron therapy agent: 1-amino-3-[(dihydroxyboryl)ethyl]cyclobutanecarboxylic acid

A novel boronated aminocyclobutanecarboxylic acid was synthesized in 10 steps for potential use in neutron capture therapy. The molecule was modeled after the unnatural amino acid 1-aminocyclobutanecarboxylic acid, which has shown high uptake in brain tumors.     

Synthesis and application in SPPS of a stable amino acid isostere of palmitoyl cysteine

(S)-2-Amino-4-(2-pentadecyl-1,3-dioxolan-2-yl)-butanoic acid, 11, Pdiob, a synthetic analogue C-isostere of palmitoylated cysteine, has been prepared starting from tetrabenzyl glutamic acid. The less hindered benzyl carboxylate ester was transformed into the corresponding β-ketophosphonate and subjected to a Horner-Wadsworth-Emmons reaction followed by hydrogenation/hydrogenolysis. This product was used for the preparation on solid phase and under microwave dielectric heating of a highly lipidated peptide that can be considered as an acid stable analogue of the C-terminus of the H-Ras heptapeptides 180-186.     

Simple and effective preparation of amino sulfonylureas from amino acids: application to the synthesis of amino sulfonylurea-containing peptidomimetics

Several amino sulfonylureas have been synthesized, starting from amino acids. The synthetic procedure is simple affording high yields of products under mild conditions. Furthermore, it is shown that these compounds can be incorporated into a peptide sequence.     

Synthesis of novel amino squaric acids via addition of dianion enolates derived from N-Boc amino acid esters

Novel α-amino squaric acid analogs were synthesized by initial addition reaction of a dianion enolate generated from N-Boc amino acid tert-butyl ester to squaric acid diisopropyl ester, and subsequent decarboxylation of the resulting carboxylic acid moiety.     

Synthesis of novel water-soluble linear and heterocyclic phosphino amino acids from 2-phosphinophenols or 2-phosphinophenolethers, formaldehyde and amino acids

Acyclic and cyclic amino acid derivatives of 2-phosphinophenols have been synthesised by reaction of primary phosphinophenols (4-R-2-H₂PC₆H₃OH; R=H, Me, OMe) 1a–c with formaldehyde and amino acids (o- and p-aminobenzoic acid, -lysine) via in situ formed hydroxymethyl species 2a–c. Condensation reactions with glycine did not afford defined products except when the methoxymethyl and tetrahydropyranyl ethers of 1d,e were used instead of the hydroxy compounds. o-Aminobenzoic acid gives rise to linear bis(o-carboxyphenylaminomethyl)phosphines 3a–e. p-Aminobenzoic acid, dependent on the molar ratio, affords bis(p-carboxyphenylaminomethyl)phosphines 4a,d as well as eight-membered heterocyclic 1,5,3,7-diazadiphosphacyclooctanes 5a–e. The aliphatic amino acids glycine and -lysine form six-membered heterocyclic 1,3,5-diazaphosphorinanes 6d and 7a–e, respectively, in presence of excess formaldehyde. -lysine differs from glycine by reaction at the terminal amino group. The structures of the compounds have been elucidated by multinuclear NMR spectroscopy. The salts of the phosphino amino acids are soluble in water. Water solubility increases with the number of hydrophilic groups, i.e. free phenols are more soluble than their ethers. Ligand concentrations in water from 0.1 to 1 M were observed.     

Synthesis of enantiopure free and N-benzyloxycarbonyl-protected 3-substituted homotaurines from naturally occurring amino acids

Enantiopure N-benzyloxycarbonyl-protected and free 3-substituted homotaurines were synthesized from naturally occurring amino acids via N-benzyloxycarbonyl protection, Arndt–Eistert homologation, reduction, esterification with thioacetic acid, and oxidation with performic acid. The current method is a convenient, practical, and salt-free method for the synthesis of enantiopure 3-substituted homotaurine with moderate to good yields.     

Synthesis of novel fullerene amino acids and their multifullerene peptides

[60]-Fullerene functionalized amino acids with 4-6 methylene spacers from α-carbon to the nitrogen atom of fulleropyrolidine and corresponding multifullerene peptides have been synthesized.     

反相流动注射-化学发光法测定氨基酸

基于碱性条件，氨基酸对次氯酸钠-一鲁米诺化学发光体系的显著增敏作用，建立了反相流动注射-化学发光法测定氨基酸的新方法。该法不需对氨基酸进行衍生或转化，检出限为0．016μg/mL，采样频率为150次／h，对1μg／L的组氨酸进行连续12次平行测定，其RSD为0．9％。对氨基酸注射液样品中的氨基酸测定的回收率在98．6％～102．1％之间，并和经典的茚三酮比色法进行了对照。     

Synthesis of 2,3,6-trisubstituted pyridines by transition-metal free cyclization of 1,3-diynes with amino acids

Amino acids are firstly employed in transition-metal free heterocyclization reaction of 1,3-diynes in the presence of K₃PO₄ and DMSO at 120 °C. This method produces 2,3,6-trisubstituted pyridines with up to 86% yield. The –CO₂H group on the amino acids is crucial for this heterocyclization reaction. The mechanism of such a heterocyclization reaction is discussed, as well.     

Catalyst and solvent-free amidation of inactive esters of N-protected amino acids

A catalyst free procedure for the preparation of amides from inactive esters of N-protected amino acids and various amines is demonstrated under mild reaction conditions. Our effort to recover excess amine and generated alcohol is an approach towards environment friendly and cost effective synthesis under easy operational conditions.     

Production and utilization of amino acids.

The amino acid industry has been steadily expanding since monosodium glutamate was first marketed as a flavoring material in 1909. Its production has recently reached almost the 1 billion dollar level. Amino acids are produced by extraction from protein hydrolyzates, by fermentation with the aid of microorganisms, by enzymatic processes, and by chemical synthesis. To obtain natural L-amino acid, chemical synthesis generally requires two additional steps, i.e. optical resolution and racemization of the D isomer. The most important applications of amino acids include the fortification of plant food and feeds by supplementation of the deficient essential amino acid(s). Apart from their uses in the food industry, medical applications of amino acids (nutritional preparations and therapeutic agents) are becoming increasingly important.     

Chemiluminescence determination of 20 amino acids and the mechanism study

<正>It was found that 20 amino acids could inhibit the intensity of the luminol-H_2O_2-CuSO_4 chemiluminescence system.Using this character,a rapid and sensitive method for the determination of 20 amino acids was developed with flow injection coupled with chemiluminescence detection.Under the optimal conditions,the detection limits of 20 amino acids were in the range of 4.5×10~(-7)- 4.3×10~(-10) mol/L,and the relative standard deviations were less than 3.2%.The proposed method was successfully applied to drug analysis.The possible mechanism was also discussed.     

Effect of some amino acids and peptides on silicic acid polymerization

The polymerization of silicic acid in aqueous solutions at different pH was followed by the colorimetric molybdosilicate method. The role of four amino acids (serine, lysine, proline and aspartic acid) and the corresponding homopeptides was studied. All four amino acids behave the same way and favor the condensation of silicic acid. Peptides exhibit a stronger catalytic effect than amino acids but they appear to behave in very different ways depending on the nature of side-groups and pH. Poly-lysine and poly-proline for instance lead to the precipitation of solid phases containing both silica and peptides. The role of these biomolecules on the polymerization of silicic acid is discussed in terms of electrostatic interactions, hydrogen bonds and solubility.     

Multiparametric analysis of amino acids and organic acids in rat brain tissues using GC/MS

Using design of experiment (DOE) theory coupled with multivariate statistical analysis, we have developed a simple and reliable GC/MS-based analytical assay for simultaneous analysis of amino acids and organic acids in rat brain tissue samples. The process of water extraction (pH 10.0) was extensively evaluated using brain tissue samples and a set of 21 reference standards. Acceptable calibration curves were obtained over a wide concentration range, 0.2-35.0 microg/mL for standards and 15.0-2.4 mL/g (tissue) for brain tissue samples. The precision was mostly better than 10% for both the mixed standards and the brain tissue samples. The brain tissue samples exhibited good stability within 48 h with RSD generally less than 15%. Furthermore, the developed analytical method was successfully applied in distinguishing the subtle variation among different parts of the brain tissues, such as cerebral cortex, hippocampus, and thalamus.     

Separation of native amino acids at low pH by capillary electrophoresis

Amino Acids are cations at low PH and can be readily separated by capillarty electrophoresis provided an alkanesulfonic acid is added to the elecrolyte carrier. Formation of a Positive net charge on the bare fused-silica surface at low PH was confirmed by measurement of an anodic electroosmotic flow. The addition of ethanesulfonic acid or octanesulfonic acid to the electrolyte carrier causes a reversal of the EOF. A mechanism is proposed in which the alkanesulfonic acid adsorbs to the positively-charged capillary wall through electrostatci attraction. Adsorption of a second molecule of alkanesulfonate by hudrophobic attraction to the carbon chain forms a negatively-charge coating on the capillary wall. The alkanesuflfonate also imparts selectivety to the system by participation in ionpairing interactions with the native amino acids to improve resolution. The CE separation of a mixture of the twenty common amino acids at PH 2.8 with direct absorabance detection at 185 nm resulted in 17 amino acid peals in 20 minutes with a 30 KV applied voltage. The effect of several variables was studied including electrolyte carrieres containing different alkanesulfonic acids, the influence of PH, applied voltage, and concentration of electrolyte carrier.     

Synthesis of N-alkylated amino acids using fluorous-tagged hydroxylamines

The development of a new fluorous-tagged ammonia-equivalent for the synthesis of N-alkylated amino acids is described. The required building blocks were readily accessed in high yield and purity using F-SPE purification technique. Coupling of the fluorous-tagged hydroxylamines with a selection of boronic acids and glyoxalic acid gave the desired N-alkylated amino acids. Subsequent removal of the fluorous tag via catalytic hydrogenation was investigated using a number of different catalysts and solvents. A more robust de-tagging procedure involves the transformation of the amino acid to the corresponding methyl ester followed by a Mo(CH₃CN)₃(CO)₃ mediated N-O bond cleavage.     

Lipophilicity determination of some fully protected peptides and amino acids

Summary The lipophilicity of 21 fully protected peptides and amino acids was determined by reversed-phase thin-layer chromatography. The R_M values decreased linearly with growing methanol concentration of the eluent. The sequence and conformation of molecular substructures did not significantly influence the lipophilicity. The presence of salt and ammonia in the eluent had a negligible impact on retention; the effect of the pH value was also low. In the presence of 1M and 2M acetic acid the retention of each compound considerably decreased. Acetic acid also changed markedly the selectivity. Our data suggest that the acetic acid has a preponderant role in changing the retention and selectivity of fully protected peptides and amino acids in reversedphase thin-layer chromatography.     

Probing the weak interactions between amino acids and carbon monoxide

The relatively weak interactions between some non-charged amino acids with CO were investigated theoretically by using density functional theory （DFT） method. The stretching frequency of CO correlates well with its bond length followed the Badger＇s rule, and the correlation between binding energy and Mulliken charge partition of CO was also investigated for the first time. 2007 Ying Wu Lin. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.