Synthesis of sequential oligopeptides and polypeptide having the sequence of L-alanyl-L-leucylglycine

A series of sequential oligopeptides having simple nonpolar side chains, Nps-(L -Ala-L -Leu-Gly)_n- OEt has been prepared by a stepwise fragment-condensation method using Nps-L -alanyl-L -leucylglycine N-hydroxysuccinimide ester, which was prepared by the Nps-N-carboxy α-amino-acid-anhydride method. The success of the synthesis of the peptide having a high-molecular weight, such as octadecapeptide, results from the highest solubility of the tripeptide unit, L -alanyl-L -leucylglycine. The sequential polypeptide having the same tripeptide sequence was also prepared by polycondensation of the tripeptide N-hydroxy-succinimide ester.     

Synthesis of N-hydroxysuccinimide esters of phosphatidylethanolamine and some properties of liposomes containing these derivatives

The N-hydroxysuccinimide (NHS) ester of N-suberyl-dimyristoylphosphatidylethanolamine (sub-DMPE) was synthesized by reaction of DMPE with disuccinimidyl suberate, and isolated by preparative plate chromatography. Liposomes, which contain NHS-sub-DMPE, can covalently bind compounds that possess a free amino group such as ε-dinitrophenyl-lysine. The extent of DNP-lysine binding is influenced by the time and temperature of incubation, the amount of NHS-sub-DMPE incorporated into the liposomes, and the initial concentration of DNP-lysine. Binding occurs as a consequence of the formation of a new dinitrophenylated compound which has been characterized. Although NHS-sub-DMPE is stable to storage in organic solvents, preformed liposomes rapidly lose their ability to bind DNP-lysine due to hydrolysis of the N-hydroxysuccinimide ester bond. These findings bear on the future applicability of liposomes, containing N-hydroxysuccinimide esters of PE, as illustrated by the preparation of immunogenic liposomes.     

Aminomethyl coumarin acetic acid: A new fluorescent labelling agent for proteins

Summary A new fluorescent protein labelling agent, 7-amino-4-methyl coumarin-3-acetic acid (AMCA), emits in the blue region (440–460 nm) on activation with UV light (350 nm). The active reagent is theN-hydroxysuccinimide ester which reacts with lysine residues under mild conditions to form photostable amide links.The Stokes shift of 100 nm compared to 30 nm for Fluorescein isothiocyanate (FITC) allows easy filter discrimination of exciting and emitting radiation. The agent has been demonstrated in use for fluorohistochemical examination of human kidney glomeruli, using the sandwich technique and compared with the same procedure using FITC-labelled antibodies. The good quantum yield coupled with convenient emission lines in the mercury spectrum allows photographic exposure time of fluorescent labelled sections to be reduced to a quarter of that required for a corresponding FITC conjugate.AMCA—immunoglobulin conjugates were not susceptible to photobleaching and have a storage life at – 20° C of more than two years.To whom correspondence and reprint requests should be addressed.     

Tryptic peptide mapping of picomolar quantities of protein labeled with the Bolton-Hunter reagent

Characterization of 5 to 25 pmol of purified proteins by tryptic peptide mapping has been accomplished using the Bolton-Hunter reagent (¹²⁵I-3-[4-hydroxyphenyl]propionic acid N-hydroxysuccinimide ester). Radioacylation is followed by reaction with unlabeled ester and reductive methylation to ensure resistance of lysyl residues to trypsinization. Reduced and alkylated proteins are analzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, trypsinized from individual gel slices, and mapped two-dimensionally on thin layers. The method permits peptide mapping of proteins with specific activities of 1 to 2 × 10⁴ cpm/ng, results in more spots (and often more structural information) than direct iodination procedures, and can be used for characterization of proteins that could not be biosynthetically labeled.     

Isolation of isoaccepting tRNAs

The N-hydroxysuccinimide ester of succinated polyethylene oxide (polyethylene glycol 6000) has been prepared. The ester has been used to make the N-acyl derivatives of valyl-tRNA and phenylalanyl-tRNA from E. coli K-12. Because of the large molecular weight, high solubility in phenol, and the binding to Corning porous glass of polyethylene oxide, the acyl derivative, N-(succinated polyethylene oxide)-aminoacyl-tRNA, has been separated from unreacted tRNA. Since the reaction is reasonably specific for the amino group of the amino acid, large purifications have been obtained for tRNA_val and tRNA_phe. Evidence is presented to show that the ester can react with tRNA at a slow rate. The limitations on the purification due to this reaction are quantitatively evaluated. The highest ratios, pmoles aminoacyl-tRNA/ OD₂₆₀, obtained for valyl-tRNA and phenylalanyl-tRNA were 800 and 360.     

E. coli tRNAPhe modified at the 3-(3-amino-3-carboxypropyl)uridine with a photoaffinity label is fully functional for aminoacylation and for ribosomal interaction

E. coli tRNA^Phe was modified at its 3-(3-amino-3-carboxypropyl)uridine residue with the N-hydroxysuccinimide ester of N-4-azido-2-nitrophenyl)glycine. Exclusive modification of this base was shown by two-dimensional TLC analysis of the T₁ oligonucleotide and nucleoside products of nuclease digestion. The fully modified tRNA could be aminoacylated to the same level as control tRNA. The aminoacylated tRNA was as active as control tRNA in non-enzymatic binding to the P site of ribosomes, and in EFTu-dependent binding to the rirobosomal A site. The functional activity of this photolabile modified tRNA allows it to be used to probe the A and P binding sites on ribosomes and on other proteins that interact with tRNA. Crosslinking to the ribosomal P site has been shown.     

Cleavable ester-linked magnetic nanoparticles for labeling of solvent-exposed primary amine groups of peptides/proteins

To study the solvent-exposed lysine residues of peptides/proteins, we previously reported disulfide-linked N-hydroxysuccinimide ester-modified silica-coated iron oxide magnetic nanoparticles (NHS–SS–SiO₂@Fe₃O₄ MNPs). The presence of a disulfide bond in the linker limits the use of disulfide reducing agent during protein digestion and allows unwanted disulfide formation between the MNPs and protein. In the current work, the disulfide bond was replaced with a cleavable ester group to synthesize NHS ester-modified SiO₂@Fe₃O₄ MNPs. Use of the cleavable ester group provides an improved method for protein labeling and allows the use of disulfide reducing agents during protein digestion.     

A new method of iodinating collagens for use in radioimmunoassay.

Purified collagens from a variety of species were iodinated to a high specific activity with the N-hydroxysuccinimide ester of I¹²⁵-labeled p-hydroxyphenyl propionic acid (Bolton-Hunter reagent). Labeling had no effect on the immunoreactivity of the collagen as determined by hemagglutination inhibition. This compound presumably acylates the abundant ?-amino groups of lysyl and hydroxylysyl residues in the collagen molecule. Using this method it is possible to label pepsin-extracted collagen from which the terminal nonhelical extensions containing tyrosine have been cleaved. The application of Bolton-Hunter-labeled collagens to radioimmunoassay of affinity-purfied antibodies against collagen is demonstrated.     

Submicron patterning of DNA oligonucleotides on silicon

The covalent attachment of DNA oligonucleotides onto crystalline silicon (100) surfaces, in patterns with submicron features, in a straightforward, two-step process is presented. UV light exposure of a hydrogen-terminated silicon (100) surface coated with alkenes functionalized with N-hydroxysuccinimide ester groups resulted in the covalent attachment of the alkene as a monolayer on the surface. Submicron-scale patterning of surfaces was achieved by illumination with an interference pattern obtained by the transmission of 248 nm excimer laser light through a phase mask. The N-hydroxysuccinimide ester surface acted as a template for the subsequent covalent attachment of aminohexyl-modified DNA oligonucleotides. Oligonucleotide patterns, with feature sizes of 500 nm, were reliably produced over large areas. The patterned surfaces were characterized with atomic force microscopy, scanning electron microscopy, epifluorescence microscopy and ellipsometry. Complementary oligonucleotides were hybridized to the surface-attached oligonucleotides with a density of 7 × 10¹² DNA oligonucleotides per square centimetre. The method will offer much potential for the creation of nano- and micro-scale DNA biosensor devices in silicon.     

Poly(L-histidyl-L-alanyl-α-L-glutamic acid). I. Synthesis

Poly(L -histidyl-L -alanyl-α-L -glutamic acid) has been prepared in order to test the acid–base catalytic ability of a carboxyl-imidazole hydrogen-bonded system. Two different blocked histidyl-alanyl-glutamic acid monomers were used in the polymerization step. The imidazole ring was blocked with either a dinitrophenyl or a t-butyloxycarbonyl group. The γ-carboxyl of glutamic acid was protected as the benzyl ester. Both the coupling reactions and the polymerization step were via the N-hydroxysuccinimide active ester method. Thiolysis removed the dinitrophenyl group, while hydrogen bromide removed the t-butyloxycarbonyl and the benzyl groups. The water-soluble unblocked polymers obtained were fractionated on Sephadex G-50 or Bio-Gel P30. Fractions within a range of average molecular weights of 2,000 to 25,000 were isolated. Enzymatic oxidation of the acid hydrolyzate of the polymers revealed that no detectable racemization had occurred.     

The labelling of proteins to high specific radioactivities by conjugation to a 125I-containing acylating agent. Application to the radioimmunoassay

1. A new method is described for labelling proteins to high specific radioactivities with ¹²⁵I. The protein is treated with a ¹²⁵I-labelled acylating agent, iodinated 3-(4-hydroxyphenyl)propionic acid N-hydroxysuccinimide ester, which reacts with free amino groups in the protein molecule to attach the ¹²⁵I-labelled groups by amide bonds. 2. Three protein hormones have been labelled by this method, human growth hormone, human thyroid-stimulating hormone and human luteinizing hormone. Specific radioactivities of up to 170, 120 and 55μCi/μg respectively have been obtained for these hormones. 3. The immunoreactivity of these labelled hormones has been investigated by using a radioimmunoassay system specific for each hormone. These preparations have also been compared with and found to be equal or superior to labelled hormones prepared by chemical substitution of ¹²⁵I into tyrosine residues of the proteins by using the chloramine-t-oxidation procedure. 4. With some antisera the immunoreactivity of the antigen was diminished by the introduction of a single I atom into the tyrosyl groups, whereas antigen containing a single ¹²⁵I-labelled 3-(4-hydroxyphenyl)propionamide group showed the same immunoreactivity as the unmodified antigen.     

Bovine serum albumin-bovine hemoglobin conjugate as a candidate blood substitute

A bovine serum albumin-bovine hemoglobin conjugate was prepared using 3-maleimidobenzoic acid N-hydroxysuccinimide ester as cross-linker. The conjugate was purified using DEAE Sepharose. It had an M _r of 127 kDa. Its P₅₀ (half-saturated O₂ pressure) value and Hill coefficient were 27 mm Hg and 2, respectively.     

Synthesis of optically pure chrysobactin and immunoassay development

Chrysobactin (-N-(2,3-dihydroxybenzoyl)-d-lysyl-l-serine), a siderophore that is essential for systemic virulence by plant pathogenic Erwinia chrysanthemi, was synthesized with high diastereomeric purity. Chrysobactin was prepared by coupling the N-hydroxysuccinimide ester of -N-(2,3-dibenzyloxybenzoyl)--N-Cbz-d-lysine with l-serine benzyl ester followed by deprotection via hydrogenolysis. Optically pure chrysobactin was obtained with 98% overall yield. A monoclonal antibody to ferric chrysobactin was developed and characterized as IgM. The antibody reacts with chrysobactin, ferric chrysobactin and less strongly with ferric dihydroxybenzoic acid. The antibody reacts weakly with the siderophores ferrichrome, A, ferric pseudobactin and ferric rhodotorulic acid. This antibody was used in a competitive immunoassay to detect ferric chrysobactin at 10^–8 to 10^–10 mol. This immunoassay may provide a useful method for the detection of chrysobactin in plant samples.     

Iodotyrosylation of peptides using tertiary-butyloxycarbonyl-l-[125I]iodotyrosine N-hydroxysuccinimide ester

A rapid method for the iodotyrosylation of peptides using tertiary-butyloxycarbonyl-l-[¹²⁵I]-iodotyrosine N-hydroxysuccinimide ester is described. The method, like that of Bolton and Hunter (1973, Biochem. J.133, 529–539), uses nonoxidizing conditions, is applicable to tyrosine-free peptides, and results in an easily isolated product with decreased cationic charge. The present method has the additional advantage that the derivatized peptide is readily deblocked to form a radiolabeled product with the same net charge as the starting material.     

3-([3-125I]iodo-4-hydroxyphenyl)propionyl carbohydrazide,a new radioiodination reagent for ultrasensitive detection and determination of periodate-oxidized nucleoside derivatives and other carbonyl compounds

A new radioiodination reagent for the identification and quantitation of periodate-oxidized ribonucleosides was developed. The reagent, 3-([3-¹²⁵I]iodo-4-hydroxyphenyl)propionyl carbohydrazide, was prepared by radioiodination of 3-(4-hydroxyphenyl)propionic acid N-hydroxysuccinimide ester in the presence of chloramine T, followed by reduction of the latter with sodium arsenite and treatment of the radioiodinated ester with an excess of carbohydrazide. The reagent reacted quantitatively with periodate-oxidized nucleosides to form ¹²⁵I-labeled morpholine derivatives which were separated by thin-layer chromatography and quantitated by liquid scintillation counting. The reagent was found to react also with other carbonyl compounds and thus may find more general application in the qualitative and quantitative ultramicroanalysis of aldehydes and ketones.     

The use of azidoarylimidoesters in RNA-protein cross-linking studies with Escherichia coli ribosomes

A series of related hetero-bifunctional RNA-protein cross-linking reagents has been prepared, carrying an imidoester or N-hydroxysuccinimide ester function at one end of the molecule, and a phenylazido function at the other. These compounds have been applied to RNA-protein cross-linking studies with ribosomal subunits, and one of them, p-azido-phenylacetic imidoester, has proved to be a particularly useful reagent for this purpose. The reagent first reacts specifically with protein amino groups, and subsequent photolysis of the azide group leads to cross-linking to the RNA in yields of up to 8% of the total protein. The whole reaction takes place under very mild conditions in aqueous solution.The individual proteins concerned in the cross-links have been identified by two-dimensional gel electrophoresis, and the existence of a covalent cross-link was confirmed by the isolation by two different methods of protein-oligonucleotide complexes carrying a ³²P label. Although most of the ribosomal proteins could be cross-linked to their corresponding ribosomal RNA within the individual subunits, RNA-protein cross-links at the ribosomal subunit interface were only detectable in vanishingly small amounts.The advantages of this type of genuine hetero-bifunctional reagent in RNA-protein cross-linking studies are discussed.     

Characteristics of xanthan gum-based biodegradable superporous hydrogel

A novel biopolymer-based superporous hydrogel (SPH) was synthesized through chemical crosslinking by graft copolymerization of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) on to xanthan gum (XG) via redox initiator system of ammonium persulfate (APS) and N, N, N′, N′-tetramethylethylenediamine (TMED), in the presence of N, N′-methylenebisacrylamide (MBA) crosslinking agent, sodium bicarbonate foaming agent, a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene as a foam stabilizer. Characterization of SPH was done by FT-IR, TGA, SEM, HPC and GCMS. The effects of pH and salinity on the swelling aptitude of the SPH were investigated along with its degradability in Streptococcus bovis medium.     

Synthesis and antiviral activity of novel glycyrrhizic acid conjugates with D-amino acid esters

Glycyrrhizic acid (GA) conjugates with methyl and ethyl esters of D-amino acids (D-Trp, D-Phe, D-Tyr, D-Val, D-Leu) have been synthesized by the activated esters method using mixtures of N-hydroxybenzotriazole or N-hydroxysuccinimide with N,N′-dicyclohexylcarbodiimide. GA conjugate with D-Trp ethyl ester exhibited antiviral activity against influenza viruses A/H3N2, A/H1N1/pdm09, A/H5N1, B (SI > 10–29), and HRSV (SI > 25). GA conjugate with D-Trp methyl ester inhibited influenza virus A/H1N1/pdm09 (SI > 30).     

Asymmetric Synthesis and Biological Activity of l-Bicyclocarba-d4T

Novel l-bicyclocarba-d4T (1), an enantiomer of d-N-MCd4T has been enantiopurely synthesized as a potent anti-HIV agent starting from (R)-epichlorohydrin using tandem alkylation, chemoselective reduction of ester in the presence of lactone functional group, Grignard reaction, RCM reaction, and Mitsunobu reaction as key steps. l-N-MCd4T (1) was found to be very potent anti-HIV-1 (EC₅₀ = 6.76 μg/mL) agent with no cytotoxicity.     

Synthesis of 2-acetamido-1-N[N-(tert-butoxycarbonyl)-l-aspart-1-oyl-(l-phenylalanyl-l-serine methyl ester)-4-oyl]-2-deoxy-β-d-glucopyranosylamine and analogs

2-Acetamido-1-N-[N-(tert-butoxycarbonyl)-l-aspart-1-oyl-(l-phenylalanyl-l-serine methyl ester)-4-oyl]-2-deoxy-β-d-glucopyranosylamine and analogs containing d-glucopyranosyl, 4-O-β-d-glucopyranosyl-d-glucopyranosyl, l-Phe-l-Ala, and d-Phe-l-Ser were synthesized by condensation of glycosylamines having free hydroxyl groups with tripeptide esters activated with N-hydroxysuccinimide.