Potentiometric titration of peptides and the starting materials and intermediates of their synthesis. I. Acidimetric determination of N-acetylamino acids

The potentiometric titration of N-acetylamino acids and their sodium salts in nitromethane-acetic anhydride (2:1) with a nitromethane solution of perchloric acid has been investigated. A procedure has been developed for the quantitative determination of N-acetylamino acids in the presence of acetic acid in aqueous solutions. A differentiation determination of N-acetylamino acids and their salts in the presence of sodium acetate has been carried out.     

Esterification of C2−C16 dicarboxylic acids to n-butyl esters in aqueous solutions for their gas chromatographic analysis

Summary C₂–C₁₆ dicarboxylic acids were esterified in aqueous solution in the presence of sulfuric acid. Esterification in water/n-butanol mixtures with mole ratios between 0.02 and 2.53 can be utilized for the quantitative determination of the dicarboxylic acids by gas chromatography. The presence of water does not interfere at water/n-butanol mole ratios below 0.27. For mole ratios above 0.27 anhydrous sodium sulfate has been used for binding the water. The mole ratio range was 0.25–0.75 for anhydrous sodium sulfate/water, and 0.32–1.3 for sulfuric acid/anhydrous sodium sulfate.     

Bisacylation of the anhydride and esters of 4-methyl-1,2,3,4-tetrahydrophthalic acid

The bisacylation of the anhydride and esters of 4-methyl-1,2,3,4-tetrahydrophthalic acid by anhydrides of carboxylic acids in the presence of perchloric acid results in the formation of derivatives of 1,3-dialkyl-6, 7-dicarboxy-5,6,7,8-tetrahydro-2-benzopyrylium salts. Some reactions of the salts obtained, including their recyclization under the action of nucleophiles, have been studied. A convenient preparative method for the synthesis of 6,7-dicarboalkoxy-5,6,7,8-tetrahydroixoquinolines has been developed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1318–1321, October, 1984.     

Clouding behavior of nonionic–cationic and nonionic–anionic mixed surfactant systems in presence of carboxylic acids and their sodium salts

The study is focused on evaluation of clouding phenomena of the aqueous single nonionic surfactant system Triton X-100 (TX-100) and its mixed systems with anionic aerosol-OT (AOT) and cationic dodecylpyridinium chloride (DPC) in presence of hydrophobic ions furnished by sodium salts of carboxylic acids, viz., sodium ethanoate, sodium propanoate, sodium butanoate, and sodium hexanoate and the respective carboxylic acids [ethanoic acid, propanoic acid, butanoic acid, and hexanoic acid]. The influence of salts on the cloud point (CP) has been explained on the basis of salt effect as well as the solubilization of higher alkyl chain hydrophobic ions furnished by these salts. Moreover, the co- and counterion effect has been taken into account to explain the variation of the CP in the mixed systems. However, the effect of acids on CP has been explained in the light of their aqueous solubility and their partitioning ability between octanol and water as reflected by their K _OW values.     

Esterification of aliphatic hydroxy acids to n-butyl esters in aqueous solutions for their gas chromatographic analysis

Summary Aliphatic hydroxy acids were esterified in aqueous solution in the presence of sulfuric acid. Esterification of lactic, tartronic malic and citric acids in water/n-butanol mixtures with mole ratios between 0.02 and 2.53 can be utilized for the determination of these aliphatic hydroxy acids by gas chromatography. Water does not interfere at water/n-butanol mole ratios below 0.02. For mole ratios above 0.02 anhydrous sodium sulfate is used for the binding of water. The mole ratio range was 0.25–2.53 for anhydrous sodium sulfate/water, and 0.32–1.27 for sulfuric acid/anhydrous sodium sulfate.     

Hydrogenation of 4-(2-furyl)-2-oxobutenoic acid sodium salt on Raney nickel

The hydrogenation of 4-(2-furyl)-2-oxobutenoic acid sodium salt on a nickel catalyst has been studied. Using Raney nickel catalyst, the corresponding salts of 4-(2-furyl)-2-oxobutanoic acid, 4-(2-furtyl)-2-hydroxybutanoic acid, and aliphatic hydrogenolysis products of the initial compound were obtained. The sodium salt of 2-hydroxy-4-(2-tetrahydrofuryl) butanoic acid and the condensation product 4-(2-furylethyl)-3-(2-furylmethyl)-2-oxo-3,4-didehydroglutaric acid were detected in the hydrogenolysate. A method has been developed for obtaining the sodium salts of 4-(2-furyl)-2-oxobutanoic and 4-(2-furyl)-2-hydroxybutanoic acids.Latvian Institute of Organic Synthesis, Riga LV-1006, e-mail: elmira@osi.lanet.lv. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 41–45, January, 1998.     

Kinetics of the formation of pantolactone from pantothenates and its quantitative determination

The conditions of hydrolysis and lactonization of the calcium and sodium salts of pantothenic and pantoic acids have been studied. The selected conditions of hydrolysis (t=80°C, C_HCl=13%) led to a 100% yield of -alanine and pantothenates after 60 min from the beginning of hydrolysis, while the formation of pantolactone was complete in 105 min for the calcium salt and in 75 min for the sodium salt. The hydrolysis and lactonization reactions have been performed under the conditions mentioned, and the GLC of the pantolactone formed has permitted the determination of various concentrations of calcium pantothenate. The results obtained from the GLC analysis of pantolactone indicate the possibility of a quantitative determination of salts of pantothenic and pantoic acids. The sensitivity of this method is 0.2–5 nmole.Department of Metabolic Regulation, Academy of Sciences of the Belorussian SSR, Grodno. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 93–95, January–February, 1984.     

Transformations of hetarylideneoxazolones

Hetarylideneoxazolones are converted to hetarylideneamino acid esters by methanolysis in the presence of sodium. Alkaline hydrolysis in aqueous alcohol gives the corresponding amino acids. Hydrazinolysis of pyranylideneoxazolone gives pyranylideneamino acid hydrazide. Complete hydrolysis of oxazolone gives formylpyran, the methylation of which gives the methoxymethylpyrylium salt. Benzamidomethyl-substituted pyrylium salts were obtained by treatment of the hetarylideneamino acids with perchloric acid.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 757–763, June, 1976.     

New isoindologens in the synthesis of tetrabenzoporphins

Isoindoline hydrochloride reacts with paraformaldehyde, mesoxalic acid hydrate, N-methylformanilide, diphenylformamide, and methylene iodide in the presence of zinc acetate to give zinc tetrabenzoporphin and with sodium phenylacetate or tribenzylamine to give zinc meso-tetraphenyltetrabenzoporphin. These products are formed, respectively, from o-formylbenzoic acid and ammonium salts of malonic and phenylacetic acids. 1-Imino derivatives of isoindoline react with malonic acid to give mixtures that contain the corresponding tetrabenzoporphins, their mono- and triaza derivatives, and phthalocyanines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1372–1377, October, 1985.     

Investigation and radiometric determination of saturated and unsaturated aliphatic monocarboxylic acids and aromatic dicarboxylic acids

Investigations have been carried out on the precipitation of calcium salts of saturated and unsaturated aliphatic monocarboxylic acids and of aromatic dicarboxylic acids. The optimum ethanol/water solvent ratio has been studied at which the sodium, ammonium or triethylammonium salts of the acids have a good solubility, whereas the calcium salts are poorly soluble and can be precipitated. Based on these investigations the radiometric determination of formic acid, palmitic acid, stearic acid, methacrylic acid, oleic acid, and o-, m- and p-phthalic acids has become possible. A linear correlation has been found between the solubilities of the calcium salts of o-, m- and p-phthalic acids and the dielectric constant of the solvent mixture. CaCl₂ solution labelled with⁴⁵CaCl₂ was used for the titrations, with a solvent composition identical to that of the solution to be titrated. Radiometric titrations were carried out in 0.05M solutions for dicarboxylic acids, and in 0.1M solutions for monocarboxylic acids. For palmitic and stearic acids titrations were also carried out in the 0.01M concentration range. The equipment used for titrations was capable of detecting isotopes of soft β-radiation.     

Preparation of esters of amino acids and of peptides under mild conditions

A new method for obtaining esters of N-protected amino acids and peptides from complexes of their sodium salts with 15-crown-5 that are soluble in organic solvents is proposed.A. V. Bogatskii Physicochemical Institute, Academy of Sciences of the Ukrainian SSR, Odessa. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 224–225, March–April, 1986.     

Influence of the Solvation Upon the Reaction of α-Cyclodextrin with Carboxylic Acids,Their Methyl Esters,and Their Sodium Salts in Aqueous Solution Studied by Calorimetric Measurements

The complex formation of α-cyclodextrin with carboxylic acids, their methyl esters, and their sodium salts has been studied using calorimetric titrations. The stronger solvation of the carboxylic sodium salts compared with the free acid or their methyl esters lowers the values of the reaction enthalpy and entropy. Complex formation is influenced in the positive direction by the release of “high-energy water” from the cavity of α-cyclodextrin. The values of the reaction enthalpy and entropy increase for the complex formation of α-cyclodextrin with increasing chain length of the carboxylic acids and their derivatives, and reach an approximately constant upper limit in the case of five methylene groups.     

The azo coupling of 1-aryl quaternary salts of lepidine and quinaldine and some properties of the reaction products

A series of formazans has been obtained by the coupling of 1-aryllepidinium and 1-arylquinaldinium salts with diazonium salts. The formazans have been converted by oxidation into tetrazolium salts and by the action of acids into benzotriazines. The absorption spectra in the visible region have been measured in neutral, alkaline, and acid media.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 8, pp. 1104–1111, August, 1970.     

Simple and sensitive assay for nucleic acids by use of the resonance light-scattering technique with copper phthalocyanine tetrasulfonic acid in the presence of cetyltrimethylammonium bromide

On the basis of enhancement of resonance light scattering (RLS) of copper phthalocyanine tetrasulfonic acid (CuTSPc) by nucleic acids and cetyltrimethylammonium bromide (CTMAB) under suitable conditions, a new RLS method for determination of nucleic acids in aqueous solutions has been developed. At pH 9.80–10.95 and ionic strength 0.01 mol L^–1 (NaCl), the interaction of copper phthalocyanine tetrasulfonic acid with nucleic acids in the presence of cetyltrimethylammonium bromide results in enhanced RLS signals at 282.0 nm, 383.6 nm, and 616.2 nm in the enhanced regions. It was found that the enhanced RLS intensity at 383.6 nm was proportional to the concentration of nucleic acids within suitable ranges. The limits of detection were 10.6 ng mL^–1 for fish sperm DNA and 32.4 ng mL^–1 for calf thymus DNA when the concentration of copper phthalocyanine tetrasulfonic acid was 2.0×10^–6 mol L^–1. This method is rapid, simple and sensitive. In addition, the reagents used are relatively inexpensive, stable, and easily synthesised. The method can be applied to the determination of nucleic acids in the presence of coexisting substances, and we have applied it to the determination of DNA in synthetic samples, with satisfactory results.     

Quantitative determination of carboxylate by infrared spectroscopy: application to humic acids

The carboxylate content has been determined by infrared (IR) spectroscopy in different commercial salts of carboxylic acids and also in commercial and isolated samples of soil humic acids. A linear standard curve using anhydrous sodium salicylate has been obtained from the plot of carboxylate (COO^–) concentration vs. the weight of the IR band area, using the COO^– antisymmetric stretch vibration at 1580 cm^–1. Parallel determinations of carboxy groups by the commonly used Ca(OAc)₂ method with related carboxylic acids and humic acids in the H⁺ form has been carried out for comparison. A much better sensitivity and a similar accuracy was obtained. This method is furthermore much faster, simpler and more economical, and offers in some cases a better applicability.     

New method for preparation of anhydrides and amides of carboxylic acids using carbon tetrachloride

Conclusions A new efficient method was proposed for the preparation of the anhydrides and amides of carboxylic acids in 30–97% yield, which is based on the reaction of carboxylic acids (their alkali-metal salts) with CCl₄, or with CCl₄, and an amide, in the presence of copper or iron salts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 220–223, January, 1978.     

Synthesis of 2,6-diaryl-substituted pyrylium and 4-alkox yc hromylium salts with various anions

A method is proposed for the synthesis of 2,6-diphenyl-substituted pyrylium salts and 7-hydroxy-4-ethoxychromylium salts with various anions on the basis of the condensation of ethyl orthoformate with aliphatic-aromatic ketones in the presence of acid catalysts (hydrogen chloride, hydrogen bromide, hydrogen iodide, and 92% sulfuric acid) and Lewis acids (aluminum chloride, ferric chloride, and stannic chloride).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 160–163, February, 1971.     

Acids and their functionally substituted esters fromAmaranthus cruentus seed oil

The acid composition of seed oil ofAmaranthus cruentus and the synthesis of their glycidyl and pyridinecontaining esters are studied. It is demonstrated that 67% of the total acids are C₁₈-polyunsaturated linoleic and linolenic. A new method for preparing glycidyl esters of C₁₈-unsaturated carboxylic acids is developed by reacting their salts with ECG in an aprotic medium to produce the corresponding glycidyl esters. The reaction of the glycidyl esters and pyridine salts with carboxylic and phosphonic acids produces the propanolpyridine esters of the acids that combine the properties of the acids and pyridinium salts and are promising in the search for biologically active compounds.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 217–219, May–June, 2000.     

2-Benzopyrylium salts

The acylation of esters of 3,4-dimethoxyphenylpyruvic acid with anhydrides of aliphatic acids in the presence of 70% HClO₄ leads to the formation of 3-alkoxycarbonyl-1-alkyl-6,7-dimethoxy-2-benzopyrylium salts which, on being boiled with sodium acetate inglacial acetic acid, are converted into 3-alkoxycarbonyl-1-alkyl-6,7-dimethoxyisoquinolines.For Communication XIII, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1458–1460, November, 1973.     

2-Benzopyrylium salts XI. Synthesis of 2-benzopyrylium salts and structural analogs of isoquinoline alkaloids by acylation of homoveratric acid and its derivatives

The acylation of homoveratric acid and its derivatives with carboxylic acids in the presence of polyphosphoric acid, which leads to the synthesis of 2-acylhomoveratric acids, was studied. The properties and transformations of the latter to 2-benzo-pyrylium salts and isoquinoline bases were investigated. The structural analogs of the alkaloid papaverine were synthesized.See [9] for communication X.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1601–1605, December, 1971.