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PubMed1982

Weak acid-catalyzed pyrrolidone carboxylic acid formation from glutamine during solid phase peptide synthesis. Minimization by rapid coupling.

Formation of pyrrolidone carboxylic acid (pyroglutamic acid) residues from amino-terminal glutaminyl residues in peptides was shown to be catalyzed by weak acids, but not by strong acids. During dicyclohexylcarbodiimide-mediated coupling reactions the N alpha-protected amino acid reagent accelerated this cyclization and resulted in a significant amount of chain termination. The side reaction could be minimized by accelerating the coupling reaction and simultaneously reducing the time of exposure to weak acids. The most effective procedure was to couple in dimethylformamide with the preformed symmetric anhydride of the amino acid.

Chemical Phenomena↗

PubMed1990

BOP reagent for the coupling of pGlu and Boc-His(Tos) in solid phase peptide synthesis.

The model peptide TRH was successfully synthesized using benzotriazol-1-yl-oxy-tris(dimethylamino)phosphonium hexafluorophosphate (BOP reagent). The coupling reactions were carried out in N,N-dimethylformamide or N-methylpyrrolidone. These solvents allowed the incorporation of the N-terminal pyroglutamic acid residue into the peptide chain, without using the derivative bearing the N-benzyloxycarbonyl group, which acts as a solubility promoter. A comparative racemization study showed that Boc-His(Tos) can be coupled by means of BOP reagent with less racemization than with DCC when the amount of diisopropylethylamine (DIEA) is kept minimal (same ratio of equivalents as for Boc-His(Tos), i.e. 3 equiv.). However, with the use of a larger amount of DIEA in the coupling mixture (9 equiv.), approximately 3% of epimer was found in the crude product. Our study showed that even under low DIEA conditions, the rate of coupling of the residues with BOP remained comparable to that observed with DCC.

Chemical Phenomena↗

PubMed1992

Hydrolysis of peptide esters by different enzymes.

The combined use in peptide synthesis of the Fmoc-group with methyl, benzyl or p-nitro benzyl esters is not practical because of the elimination of the Fmoc-group under basic conditions and by catalytic hydrogenation. Nevertheless the solution synthesis of peptides requires those combinations in some cases. For this purpose we have investigated enzymatic hydrolysis of some tri and tetrapeptide esters. The hydrolysis were carried out under pH-control. We measured deprotection of the carboxyl group by thermitase, porcine liver esterase, carboxypeptidase A and alpha-chymotrypsin. The main problems are to suppress proteolytic degradation of the peptide bond and to bring the protected peptides into solution. To solve both problems we used dimethylformamide and dimethylsulfoxide as cosolvents. The ratios between esterolytic and proteolytic activity were estimated under various cosolvent concentrations. Advantages of this method are to avoid side reactions of alkaline instable side chains (e.g. asparagine, glutamine), cleavage of base labile protecting groups and racemization by alkaline saponification. The enzymatic deprotection was followed by HPLC, HPTLC and titration. On a preparative scale this method gives good yields and sufficiently pure products.

Amino Acid Sequence↗

PubMed1993

Application of tryptic condensation strategy for the synthesis of alpha-melanocyte stimulating hormone.

The use of trypsin in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) paired with N,N-dimethylformamide (DMF) has been proposed for the enzymatic condensation of peptides. The tryptic condensation strategy was applied to the synthesis of the 13-peptide, alpha-melanocyte stimulating hormone (alpha-MSH), which contains two susceptible points to trypsin, in a low-water-containing solvent system, 4% H2O in HFIP/DMF (1/1, v/v). The N-terminal 8-peptide segment (S1) ending with Arg and C-terminal 5-peptide with the side-chain protections at Lys and Trp (S2) were prepared by the stepwise coupling on p-nitrobenzophenone oxime resin and by a conventional method, respectively. Both segments were condensed by the aid of trypsin. The acid component was converted into the partially protected alpha-MSH at as high as 95% conversion determined by reversed-phase HPLC. When the side-chain of Lys at the 11-position was not protected, alpha-MSH was obtained only in 35% yield, and was contaminated with products of secondary hydrolysis. Although the Lys11-Pro12 sequence was very poorly susceptible to trypsin, the side-chain of Lys had to be protected in order to be inert to trypsin under the synthetic conditions. HFIP is demonstrated as a good solvent with DMF to allow the efficient tryptic condensation of peptides. The strategy increased the value of the enzymatic condensation as practical method by avoidance of secondary hydrolysis, high dissolution of peptides and retention of activity of enzyme.

1-Propanol↗

PubMed1994

Protected peptide disulfides by oxidative detachment from a support.

A new and efficient procedure for the preparation of protected cyclized and protected symmetrical dimeric peptide disulfides is described. A thiol is immobilized onto a solid phase through coupling of the thiol function with a resin-linked trityl group. Following conventional peptide assembly using the Fmoc-strategy, detachment is performed by oxidation with iodine in a suitable organic solvent. When N,N-dimethylformamide is used as the solvent, and the peptide chain contains an acetamidomethylthio function, located N-terminally in a N alpha-(9-fluorenylmethyloxycarbonyl), or N alpha-tert-butyloxycarbonyl cysteinyl residue, or occurring in the chain, then the corresponding fully protected cyclic peptide disulfide will be obtained in high yield and purity. In other solvents (e.g. dioxane or chloroform-methanol 1:1, v/v), the iodine-mediated oxidation gave not only the cyclic product, but also substantial amounts of the parallel symmetrical dimeric peptide retaining Cys(Acm) at the two identical N-termini.

Amino Acid Sequence↗

PubMed1996

An effective organic solvent system for the dissolution of amino acids.

Dimethylformamide containing strong acids (CF3 COOH, HBF4, TosOH, etc.) and an excess of tertiary base with pK < or = 6 is an effective solvent system for the dissolution of amino acids and their derivatives. The preferable base is pyridine, which forms a system with an apparent pH of 5.3. Amino acids dissolved in this solvent system readily interact with acylating reagents (BOC(2)O, ZOSu, Fmoc-OSu and activated derivatives of N-protected amino acids). A number of BOC-, Z-, Fmoc-amino acids, as well as several dipeptides, were synthesized using this solvent system with 80-99% yields.

Acylation↗

PubMed1998

Investigation on the stability of the Dde protecting group used in peptide synthesis: migration to an unprotected lysine.

An investigation of the stability of the Dde protecting group for amines, used in solid-phase peptide synthesis, shows that an unprotected epsilon-NH2 group of lysine can acquire the Dde protection from another epsilon-NH2 group or from an alpha-NH2 group. An unprotected alpha-NH2, however, cannot remove Dde from an epsilon-NH2 function. This migration takes place during Fmoc removal from the epsilon-NH2 with piperidine and/or during the subsequent washing steps. The Dde migration is also possible in neat dimethylformamide by a direct nucleophilic attack of the free epsilon-NH2 group. Addition of piperidine to the reaction medium accelerates the side reaction, probably because of the formation of an unstable piperidine-Dde adduct. Dde migration can be prevented if the 9-fluorenylmethyloxycarbonyl is cleaved with 1,8-diazabicyclo[5.4.0]undec-7-ene for a short reaction time (2%, 3 x 3 min). Finally, this rearrangement is shown to occur both as an intra- and intermolecular reaction between peptides on the same resin bead.

Amino Acid Sequence↗

PubMed1987

Histopathological investigation of DMF-induced hepatotoxicity.

N,N-Dimethylformamide (DMF) has been implicated in the production of hepatotoxicity in male and female F344 rats. Repeated administration of dosages of 0.75 and 1.0 ml/kg DMF for up to 12 weeks produced massive liver necrosis associated with decreased body weight gain. Macroscopically, areas of necrotic change were well pronounced in every hepatic lobe, being yellowish-red in coloration, irregular in shape, and varying in size, but were most striking immediately adjacent to the porta hepatis. Among the lobes, those which were relatively small were most markedly affected, and occasionally an entire lobe was involved. Light and electron microscopic studies revealed the hepatic architecture to be occupied by massive fibrosis. There were, however, sharp lines of demarcation between surviving normal and necrotic areas. Hemosiderosis involving macrophages was accompanied by proliferative bile ductules and a number of multinucleated giant cells. The distribution and quality of the hepatic lesions produced by DMF were discussed.

Administration, Oral↗

PubMed1990

A method of determining residual monomer in acrylic resin using methyl ethyl ketone.

An improved method of extraction of residual monomer from acrylic resin has been described for determination of the concentration of residual monomer by gas chromatography. Four kinds of organic solvent selected according to their physicochemical properties (methanol, N,N-dimethylformamide, ethyl acetate and methyl ethyl ketone) were tested for their capacity to extract residual monomer at varying temperatures and time periods. Extraction with methyl ethyl ketone at 4 degrees C was found to be the most effective. The method is simpler and more effective than others reported so far, and therefore seems to be suitable for clinical laboratory use.

Acetates↗

PubMed1970

Oligodeoxyribonucleotides: chemical synthesis in anhydrous base.

The sugar hydroxyl of a methoxytrityldeoxyribonucleoside reacts with a methoxytrityldeoxyribonucleoside phosphorofluoridate in dimethylformamide and potassium tertiary butoxide to yield the protected dinucleoside monophosphate. The reaction is fast and specific, and is used in a stepwise synthesis to prepare trinucleoside diphosphate and tetranucleoside triphosphate.

Chromatography, Ion Exchange↗

PubMed2001

Rapid evolution of novel traits in microorganisms.

The use of natural microorganisms in biotransformations is frequently constrained by their limited tolerance to the high concentrations of metabolites and solvents required for effective industrial production. In many cases, more robust strains have to be generated by random mutagenesis and selection. This process of directed evolution can be accelerated in mutator strains, which carry defects in one or more of their DNA repair genes. However, in order to use mutator strains, it is essential to restore the normal low mutation rate of the selected organisms immediately after selection to prevent the accumulation of undesirable spontaneous mutations. To enable this process, we constructed temperature-sensitive plasmids that temporarily increase the mutation frequency of their hosts by 20- to 4,000-fold. Under appropriate selection pressure, microorganisms transformed with mutator plasmids can be quickly evolved to exhibit new, complex traits. By using this approach, we were able to increase the tolerance of three bacterial strains to dimethylformamide by 10 to 20 g/liter during only two subsequent transfers. Subsequently, the evolved strains were returned to their normal low mutation rate by curing the cells of the mutator plasmids. Our results demonstrate a new and efficient method for rapid strain improvement based on in vivo mutagenesis.

Dimethylformamide↗

PubMed1970

Paper chromatographic techniques for the determination of cephalothin and desacetylcephalothin in body fluids.

Paper chromatographic procedures may be used to detect cephalothin and its metabolite desacetylcephalothin in urine, plasma, synovial fluid, and cerebrospinal fluid. Protein-bound antibiotics are released from plasma, cerebrospinal fluid, and synovial fluid by dilution with an equal volume of dimethylformamide. Data are presented on the sample preparation, paper chromatographic system, and other specific techniques.

Bacillus subtilis↗

PubMed1970

Examination of the protein composition of the cell envelope of Escherichia coli by polyacrylamide gel electrophoresis.

An envelope preparation containing the cell wall and cytoplasmic membrane of Escherichia coli was obtained by breaking the cells with a French pressure cell and sedimentating the envelope fraction by ultracentrifugation. This fraction was prepared for polyacrylamide gel electrophoresis by dissolving the protein in an acidified N,N'-dimethylformamide, removing lipids by gel filtration in the same organic solvent and removing the solvent by dialysis against aqueous urea solutions. More than 80% of the total protein of the envelope fraction was recovered in soluble form. Electrophoresis on sodium dodecyl sulfate-containing gels yielded from 20 to 30 well-resolved bands of protein. One major protein band was observed on the gels. This protein had a molecular weight of 44,000 and accounted for as much as 40% of the total protein of the envelope fraction. A double-labeling technique was used to examine the protein composition of the envelope fraction from cells grown under different sets of conditions which result in large changes in the levels of membrane-bound oxidative enzymes. These changes in growth conditions resulted in only minor alterations in the protein profiles observed on the gels, suggesting that this organism is able to adapt to changes in growth environment with only minor modifications of the major proteins of the cell envelope.

Acrylates↗

PubMed1973

Homogeneity of envelope proteins of Escherichia coli separated by gel electrophoresis in sodium dodecyl sulfate.

Some envelope proteins of Escherichia coli show variable behavior in acrylamide gel electrophoresis in 1% sodium dodecyl sulfate, depending upon the conditions of the solubilization. When solubilized in 1% sodium dodecyl sulfate at 70 C for 20 min, three distinct peaks (peaks 4, 6, and 7) are seen at molecular weights of 57,800, 44,300, and 38,400, respectively. However, when the envelope fractions are solubilized in 1% sodium dodecyl sulfate at 100 C for 5 min, or when they are treated with N, N-dimethylformamide at acidic pH before solubilization by our method, only a single peak at 48,000 molecular weight is observed in the molecular weight range mentioned above. That is, peaks 4 and 7 disappear and a new peak appears at the position overlapping with peak 6. Proteins isolated from peaks 4 and 7 show the similar molecular weight shifts to the new peak by the treatment at 100 C. No other peaks show any change by the heat treatment. The increase at the new peak is completely accounted for by the decrease at peaks 4 and 7, indicating that the new peak is composed of proteins from peaks 4, 6, and 7. However, it is concluded that these three peaks consist of distinctly different proteins for the following reasons: (i) they have different amino acid compositions, (ii) they show different solubilities in the nonionic detergent, Nonidet P-40, and as shown previously, (iii) peak 6 (protein Y) is related to deoxyribonucleic acid synthesis, and (iv) proteins in peaks 4, 6, and 7 have different resistance to proteolytic enzymes. Although the reasons for the anomalous molecular weight shifts of these peaks are not well understood at present, it is important to solubilize the E. coli envelope proteins by the standard method in order to investigate their properties and functions of the envelope proteins.

Amino Acids↗

PubMed1985

Influence of organic solvent mixtures on biological membranes.

A simple experimental model was used to study the influence of organic solvents and solvent mixtures on the integrity of biological membranes. Radiolabelled membranes were prepared biosynthetically by growing Escherichia coli in the presence of 14C-oleic acid; the bulk of the radioactivity was incorporated into 14C-phosphatidylethanolamine, the predominant phospholipid species in E coli membranes. The radiolabelled bacteria were incubated at 37 degrees C in the presence of solvent, and the mixture filtrated through a Millipore 0.45 micron filter. This filtration retained radiolabel associated with the bacteria, and only radiolabel released as a result of solvent action was allowed through the filter. The radioactivity in the filtrate was then counted and expressed as a percentage of the total radioactivity. Results showed that aliphatic alcohols released membrane constituents in relation to their hydrocarbon chain length (1-propanol greater than 2-propanol greater than ethanol greater than methanol); the effects of aliphatic alcohols were potentiated by acetone, ethyl methyl ketone, ethylene glycol, and N,N'-dimethylformamide, and the effects of ethanol were potentiated by 1-butanol, benzyl alcohol, and ethylacetate. These findings point to the possibility that certain mixtures of organic solvents are more damaging to membranes than the components of the mixture would indicate, and suggest that the experimental model used might help in showing mixtures that are particularly harmful.

Acetone↗

PubMed1991

Carvedilol (Kredex) reduces infarct size in a canine model of acute myocardial infarction.

Carvedilol (Kredex) is a multiple action, antihypertensive agent that may also prove to be useful in the treatment of angina and congestive heart failure. Carvedilol combines in one molecule both beta-adrenoceptor blocking and vasodilating activities. Inasmuch as beta-adrenoceptor blocking agents are known to be cardioprotective and thereby reduce infarct size, it is logical to assume that carvedilol, likewise, would possess this desirable activity. Furthermore, the additional vasodilating activity of carvedilol could contribute to further reductions in infarct size by reducing myocardial work (and therefore myocardial oxygen demand) through reductions in both afterload and myocardial wall tension. As such, we have investigated the ability of carvedilol to reduce infarct size in a canine model of acute myocardial infarction. Carvedilol (1 mg/kg i.v.) or its vehicle, dimethylformamide, were administered 15 min before left circumflex coronary artery (LCX) occlusion. Following 1 h of LCX occlusion, dogs were reperfused through a critical stenosis and then allowed to recover for 24 h. Carvedilol-treated animals exhibited a 78% reduction in infarct size compared to vehicle controls, such that the percentage of the left ventricle infarcted was reduced significantly from 16.2 +/- 4.1% in control animals to 3.6 +/- 1.3% in animals treated with carvedilol (p = 0.017, n = 6). Stained tissue sections of the left ventricle were photographed, digitized and color-enhanced using an Image Analysis Computer System, and three-dimensional reconstruction of the left ventricle, including the infarcted areas, was performed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗

PubMed1998

Chemical modification and photograft polymerization upon expanded poly(tetrafluoroethylene).

Poly(tetrafluoroethylene) (PTFE) films were surface-modified by employing a reaction solution of benzophenone and sodium hydride in anhydrous dimethylformamide at a temperature of 150 degrees C for 12 h. Electron spectroscopy for chemical analysis (ESCA) showed defluorination, oxygen incorporation, and extensive unsaturation within the treated PTFE surfaces. The suitably of these reduced PTFE films as substrates for graft polymerization was initially assessed via photograft polymerization of the sodium salt of styrenesulfonic acid (SS-Na), which permitted unequivocal surface analysis by the introduction of a new atom, as well as poly(ethylene glycol) monoacrylate (PEG-Ac). All photograpt polymerization was performed employing ultraviolet irradiation with 2,2-dimethoxy-2-phenylacetophenone as an initiator. Photograft polymerization of SS-Na was verified by further reduction of fluorine atomic content and the appearance of new sulfur and sodium atomic peaks on ESCA survey spectra, and that of PEG-Ac was verified by further reduction of fluorine atomic content and increase of atomic percent ratio of O/C from ESCA survey spectra as well as appearance of a new ester peak on high resolution ESCA C 1s spectra. Dynamic water contact angles on reduced and PEG-Ac photograft polymerized films were measured and showed that the PTFE film surface became more hydrophilic after reduction (from 120 to 89 deg) and the reduced film became more hydrophilic after photograft polymerization with PEG-Ac (from 89 to 36 deg). Modification of the complete surface of expanded PTFE (ePTFE), i.e. of the lumenal, outside and pore surfaces, was performed by employing the reaction described above, except at 105 degrees C for 1 day, followed by photograft polymerization of PEG-Ac. ESCA was performed on the superficial surfaces (i.e. the lumen and exterior) as well as on cross-sections of the ePTFE to permit analysis of the pore surfaces. This analysis showed that both the initial surface reduction and subsequent photograft polymerization were successful as indicated from F/C and O/C atomic percent ratios from ESCA survey spectra, from overall peaks shapes of high resolution ESCA C 1s spectra and from generation of new ester peaks on high resolution ESCA C 1s spectra of ePTFE graft polymerized with PEG-Ac, which demonstrated an O/C atomic percent ratio close to that of PEG-Ac homopolymer. Low voltage scanning electron microscopy confirmed minimal morphological damage to the ePTFE microstructure after reduction and graft polymerization. The approach explored thus provides a means for modulation of biological interactions at ePTFE surfaces with only minimal modification of material morphology, with some surface texture appearing on a length scale of 50-100 nm.

Benzophenones↗

PubMedDate not supplied

CEA and NCA expressed by colon carcinoma cells affect their interaction with and lysability by activated lymphocytes.

Heterogeneous lysability by interleukin-2 activated lymphocytes (LAK) and other immune effectors was observed in the human colon-carcinoma lines LoVo/Dx, LoVo/H and HT29. The tumor cells with high susceptibility to LAK (LoVo/Dx, HT29) expressed higher amounts of the adhesion molecules ICAMl, LFA3 and NCA/CEA than cells with low LAK sensitivity (LoVo/H). Monoclonal antibodies against these molecules caused a marked reduction of lysis by LAK of LoVo/Dx and HT29. A pool of these antibodies induced a nearly complete inhibition of the LAK lysis of both lines. Treatment of LoVo/Dx with differentiating agents (dimethylformamide and retinoic acid) led to a decreased expression of the adhesion molecules, including NCA, accompanied by increased resistance to LAK-mediated lysis. Moreover, the presence of CEA soluble antigen drastically inhibited the cytotoxic activity of LAK effectors against HT29 and LoVo/Dx cells, in a dose-dependent manner. These data indicate that sensitivity of colon-carcinoma cells to activated lymphocytes depends on the level of expression of adhesion molecules, including CEA and NCA. Given the role of CEA-related antigens in tumor/lymphocyte interaction, soluble CEA, frequently released by colon-carcinoma, may be involved in immunosuppressive effects induced in vivo by tumor cells.

Antigens, Neoplasm↗