Search results for "uci"
showing 10 items of 5317 documents
Fluorenylmethoxycarbonyl-ProtectedO-Glycosyl-N-methyl Amino Acids: Building Blocks for the Synthesis of Conformationally Tuned Glycopeptide Antigens
2015
Peptide antibiotics often contain N-methylated amino acids. These N-methylamino components enhance the metabolic stability and strongly influence the conformational behavior of these peptide drugs. N-Methyl-O-glycosyl amino acids, in particular, threonine and serine derivatives, are unknown so far. Fmoc-protected N-methyl-O-glycosyl-threonine and -serine building blocks, including sialyl TN antigens, have been synthesized for the first time by converting the Fmoc-protected O-glycosyl amino acids or their tert-butyl esters into the corresponding oxazolidinones followed by reductive ring-opening. These new components are considered interesting for the construction of modified mucin glycopepti…
ChemInform Abstract: New Strategy for the Stereoselective Synthesis of Fluorinated β-Amino Acids.
2010
Racemic and chiral nonracemic α-substituted and α-unsubstituted β-fluoroalkyl β-amino acid derivatives 6 and 9 have been synthesized in two steps starting from fluorinated imidoyl chlorides 1 and ester enolates. This approach is based on the chemical reduction of previously obtained γ-fluorinated β-enamino esters 4 by using ZnI2/NaBH4 in a nonchelated aprotic medium (dry CH2Cl2) as the reducing agent. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction. The process takes place with high yields and with moderate to good diastereoselectivity. The best results related to diastereoselective reduction of chiral β-enamino esters 4…
Effects of KL4-Type Peptides on the Surface Activity and Stability of Pulmonary Surfactant Films as Evaluated in the Captive Bubble Surfactometer
2012
Although SP-B is the most critical protein in lung surfactant, recombinant or synthetic forms of SP-B as a basis for the development of therapeutic surfactants are still not available. An alternative is the design and production of peptides mimicking the structure and general properties of essential motifs in SP-B.In the present study the surface activity of different KL4-derived peptides, as sequence variations of the original peptide designed to replicate a general amphipathic motif of SP-B [1], has been assessed in the captive bubble surfactometer. The peptides were reconstituted in a surfactant lipid matrix: DPPC/POPC/POPG (50:25:15, w/w/w). This mixture was selected because it offers a…
Chromatographic Determination of Thiols After Pre‐column Derivatization witho‐Phthalaldehyde and Isoleucine
2004
Abstract The reaction of primary amines with excess o‐phthalaldehyde (OPA) and thiol yields unique isoindole derivatives that are readily separated by reversed‐phase liquid chromatography. In a previous work, a spectrophotometric procedure was proposed for the assay of N‐acetylcysteine by derivatization with OPA and isoleucine at pH 9.5, with satisfactory results. The chromatographic determination of this and other low molecular‐weight thiols, after isoindole formation with isoleucine, using mobile phases of acetonitrile–water at pH 3 and spectrophotometric detection, is now examined. From the assayed thiols (thioglycolic acid, 3‐mercaptopropionic acid, tiopronin, N‐acetylcysteine, N‐acetyl…
Use of the o-Phthalaldehyde and N-Acetyl-L-Cysteine the Evaluation of Milk Proteins
1991
Abstract o -Phthalaldehyde and N-acetyl-Lcysteine are used in the determination of milk proteins. Three procedures are proposed and compared. One of them is based on reaction of o -phthalaldehyde and N-acetyl-Lcysteine with the intact proteins and the two others on reaction of the reagents with the released amino acids after total acid hydrolysis of the protein samples. When the protein sample is hydrolyzed, calibration is performed either with a hydrolyzed protein standard or with isoleucine. A procedure for the measurement of the degree of enzymatic hydrolysis of milk proteins without separation of the unhydrolyzed protein, which makes use of the same reagents, is also described. In all c…
Direct acid-catalysed mechanical depolymerisation of fibre sludge to reducing sugars using planetary milling
2016
Abstract This study performed a direct solvent-free acid-catalysed mechanical depolymerisation of fibre sludge to reducing sugars which involves one step of acid milling in a planetary mill. The common reported ‘solvent-free’ mechanocatalytic depolymerisation of lignocellulose which includes 1) acid impregnation, 2) vacuum evaporation and 3) mechanocatalytic depolymerisation was also performed as a reference. The major converted monosaccharides were determined by capillary electrophoresis and the results of total reducing sugar (TRS) yields were carried out based on the 3,5-dinitrosalicylic acid (DNS) method. The results showed that the TRS conversion of direct acid-catalysed mechanical dep…
Pretreatment and fractionation of lignocellulosic barley straw by mechanocatalysis
2017
Abstract This study focuses on the mechanocatalytical process combining dilute acid pretreatment and mechanical processing driven by ball milling. Milled and hydrolyzed barley straw samples are subject to reducing sugar analysis by DNS assay and capillary electrophoresis. Optimization of the saccharification conditions was carried out with two different sulfuric acid concentrations, 0.5 mol kg −1 and 1.0 mol kg −1 , and compared. A significant yield of total reducing sugar (53.4%) was obtained from barley straw impregnated with sulfuric acid (1.0 mol kg −1 ) after milling for only 20 min. Glucose and xylose concentrations accounted for 3.5% and 11.3%, respectively. Strikingly, the present s…
Purification and characterization of leucine aminopeptidase from kidney bean cotyledons
1992
A leucine aminopeptidase (EC 3,4,11.1) was purified from cotyledons of resting kidney beans (Phaseolus vulgaris L. cv. Processor) by acidic extraction, ammonium sulfate fractionation and chromatography on DEAE-Sephacel, Sephacryl S-300, Mono Q HPLC and Superose HPLC columns. The yield of the 317-fold purified enzyme was 9%. On gel filtrations on Sephacryl S-300 and Superose HPLC the elution volumes of the enzyme corresponded to an M, of 360 000. The enzyme gave one band on native gel electrophoresis and an electrophoretic titration in an immobilized pH gradient gave a single curve with a pI of 4.8. Two bands were observed in an SDS-gel electrophoresis with Mr values of 58 000 and 60 000 bot…
Indirect analysis of urea herbicides from environmental water using solid-phase microextraction.
2000
We described here a solid-phase microextraction procedure used to extract six urea pesticides-- chlorsulfuron, fluometuron, isoproturon, linuron, metobromuron and monuron--from environmental samples. Two polydimethylsiloxanes and a polyacrylate fiber (PA) are compared. The extraction time, pH control, addition of NaCl to the water and the influence of organic matter such as humic acid on extraction efficiency were examined to achieve a sensitive method. Determination was carried out by gas chromatography with nitrogen-phosphorus detection. The proposed method requires the extraction of 2 ml of sample (pH 4, 14.3%, w/v, NaCl) for 60 min with the PA fiber. The limits of detection range from 0…
Determination of the protein and free amino acid content in a sample using o-phthalaldehyde and N-acetyl-L-cysteine
1990
A spectrophotometric method is proposed for determining the protein content in a sample after total acid hydrolysis. In the procedure, free amino acids are caused to react with o-phthalaldehyde and N-acetyl-L-cysteine at pH 9.5, using isoleucine as the reference compound. Correction factors are used to take into account the differences between the molar absorptivities of the amino acid isoindoles and the recoveries of the amino acids after the hydrolysis treatment. The limit of detection was in the range 40-50 micrograms of protein, and the recoveries were usually 101 +/- 3% with a coefficient of variation lower than 4%. The free amino acid content in a partially hydrolysed protein was also…