Selective reductions. 59. Effective intramolecular asymmetric reductions of alpha-, beta-, and gamma-keto acids with diisopinocampheylborane and intermolecular asymmetric reductions of the corresponding esters with B-chlorodiisopinocampheylborane

A comparison of the stereochemistry of the products obtained from the intramolecular asymmetric reduction of a series of keto acids with (-)-diisopinocampheylborane and intermolecular asymmetric reduction of the corresponding series of keto esters with (-)-B-chlorodiisopinocampheylborane ((-)-DIP-Chloride) has been made. The stereochemistry of the hydroxy acids from the reduction of keto acids is dependent only on the enantiomer of the reagent used. The stereochemistry of the products from the reduction of keto esters is also consistent, except those of aliphatic alpha-keto esters. alpha-, beta-, and gamma-keto acids provide the corresponding hydroxy acids in 77-98% ee, and the alpha- and gamma- keto esters afford the hydroxy esters in 82->or=99% ee. beta-Keto esters do not undergo reduction. Although the reduction of delta-keto acids does not proceed under the same reaction conditions, the reduction of delta-keto esters is facile. All of the products from the reduction of gamma-keto acids and esters and delta-keto esters were converted to the corresponding lactones. This study revealed that DIP-Chloride is an efficient reagent for the reduction of alpha-keto esters at low temperatures.     

3- and 4-aminocyclohexanecarboxylic acids,containing either the diethylenimidophosphoryl or the diethylimidothiophosphoryl group

Conclusions We were the first to obtain the ethyl esters of the N-dichlorophosphoryl-3(and 4)-aminocyclohexanecarboxylic acids, the ethyl esters of the N-dichlorothiophosphoryl-3(and 4)-aminocyclohexanecarboxylic acids, the ethyl esters of the N-diethylenimidophosphoryl-3(and 4)-aminocyclohexanecarboxylic acids, the ethyl esters of the N-diethylenimidothiophosphoryl-3(and 4)-aminocyclohexanecarboxylic acids, the sodium salts of the N-diethylenimidophosphoryl-3(and 4)-aminocyclohexanecarboxylic acids, and the sodium salts of the N-diethylenimidothiophosphoryl-3(and 4)-aminocyclohexanecarboxylic acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 933–935, April, 1974.     

Simple thin-layer chromatographic purification procedure for the determination of cholesterol ester fatty acid compositions

A mild procedure for the purification of methyl esters of the fatty acid components of cholesterol esters, from interfering free cholesterol and other contaminating residues, is described. Methyl esters and free cholesterol are formed during the methylation of cholesterol esters. When co-extracted, cholesterol and other contaminating residues interfere with the methyl esters because minute proportions of these residues tend to elute at the same retention times as palmitoleic and stearic acids, to yield unreliable but significantly higher values for palmitoleic (p less than 0.001) and stearic acids (p less than 0.0001), and correspondingly lower values for oleic acid (p less than 0.0001). Purification of methyl esters by thin-layer chromatography eliminates this problem and yields reliable analysis of cholesterol ester fatty acids, without measurable oxidation of unsaturated fatty acids.     

Positional isomers of thienopyrimidinones

Condensation of o-cyanomethylbenzoic acids with esters of 2-aminothiophene-3-carboxylic and 3-amino-thiophene-2-carboxylic acids to give isomeric 2-(4-oxo-3,4-dihydrothieno[2,3-d]pyrimidin-2-ylmethyl)-benzoic acids and their ethyl and phenacyl esters. Methylation of esters occurs at N-3. The spectroscopic characteristics of the positional isomers are compared at the level of carboxylic acids, their esters, and methylated products. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, 932–941, June, 2008.     

A practical synthetic approach to chiral α-aryl substituted ethylphosphonates

A convenient general method is reported for the synthesis of α-aryl substituted ethylphosphonic acids and esters by hydrogenation of α-aryl substituted ethenylphosphonic acids and esters. Racemic α-arylethylphosphonic acids and esters were prepared in 70–88% yield under palladium-assisted transfer hydrogenation conditions using ammonium formate. Asymmetric hydrogenation of α-arylethenylphosphonic acids using chiral Ru(II) catalysts led to α-arylethylphosphonic acids with enantiomeric excesses up to 86%.     

Synthesis of benzoxazoles from imino esters I. 2-Alkyl(aryl)-substituted benzoxazoles

It is found that condensation of esters of iminocarboxylic and iminoperfluorocarboxylic acids with o-aminophenol is a convenient general method for preparing 2-alkyl, 2-perfluoroalkyl, and 2-aryl substituted benzoxazoles. Hydrochlorides of esters of iminocarboxylic acids react smoothly with o-aminophenol even at room temperature. Condensation of esters of iminoperfluorocarboxylic acids, whose hydrochlorides are unstable, is suitably carried out in the presence of an equimolecular quantity of the corresponding perfluorocarboxylic acid. 2-Alkyl(aryl) substituted benzoxazoles can also be obtained by heating o-aminophenol with esters of iminocarboxylic acids in the form of free bases. Esters of iminoperfluorocarboxylic acids also react similarly. Under similar conditions diesters of bisiminocarboxylic and bisiminoperfluorocarboxylic acids and o-aminophenol giveα, ω-di(benzoxazolyl-2) alkanes, andα, ω-di(benzoxazolyl-2) perfluoroalkanes respectively.     

Reaction of β-Aroylacrylic Acids with Triphenylphosphine Hydrobromide and Certain Reactions of the Resulting Products

Triphenyl(β-aroylethyl)phosphonium bromides and esters of α-(triphenylphosphoniobromido)-β-aroylpropionic acids were synthesized by the reaction of β-aroylacrylic acids and their esters. Oximes derived from triphenyl(β-aroylethyl)phosphonium bromides were reduced into the corresponding diphenylphosphoryl derivatives.     

Analysis of amino acids as formamidene butyl esters by electrospray ionization tandem mass spectrometry.

Amino acid formamidene butyl esters are optimally prepared by heating amino acids with dimethylformamide dimethylacetal (DMF-DMA) for 2 minutes at 65 degrees C and then with n-butanol/hydrogen chloride for 15 minutes at 65 degrees C. The formamidene butyl esters of simple alpha-amino acids and beta-amino acids afford between 1.1 and 20 times the signal intensity of the corresponding butyl esters during electrospray ionization tandem mass spectral analysis. Complex alpha-amino acids, such as ornithine, arginine and citrulline, and gamma-amino acids are better analyzed as butyl esters. Secondary alpha-amino acids, such as proline and sarcosine, give a mixture of two iminium salts with the DMF-DMA derivatization method. A derivative incorporating two molecules of the amino acid predominates at higher derivatization temperatures. Contrary to a previous report, N-formylamino acids were not detected. The presence of secondary amino acids in amino acid mixtures, derivatized as formamidene butyl esters, affords derivatives that incorporate two different amino acids. The new formamidene butylation method is unlikely to replace the butylation procedure used by neonatal blood spot screening programs for amino acid disorders, since a much poorer response was obtained with formamidene butyl esters of arginine and citrulline, important in the diagnosis of arginase deficiency and citrullinaemia.     

Preparation and reactions of stannylated amino acids

Hydrostannations of propargylic glycine esters with the new hydrostannation catalyst [Mo(CO)3(CNtBu)3] (MoBI3) gave rise to alpha-stannylated allylic esters in good yield and with high regioselectivity. The chelate Claisen rearrangements of these esters allow the syntheses of gamma,delta-unsaturated amino acids with a vinylstannane moiety in the side chain. The amino acids obtained can be further modified by cross-coupling with various types of electrophiles.     

Kinetics of hydrolysis of esters of acetylalkyl- and carboxyalkylphosphonic acids

Conclusions An increased reactivity of esters of acetylmethyl- and carboxymethylphosphonic acids in a spontaneous hydrolysis and of esters of acetylalkylphosphonic acids in alkaline hydrolysis as the result of intramolecular catalysis has been established. Enol forms of the esters participate in the mechanisms of the intramolecular catalysis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 310–312, February, 1986.The authors wish to express their gratitude to T. Kh. Gazinov for providing esters (I) and (II).     

HPLC of fatty acid esters of mono- and polyhydric alcohols. Part 2: Preparative separation

This paper demonstrates how simply and rapidly fatty acid esters of mono- and polyhydric alcohols can be separated quantitatively in preparative quantities on Lobar® RP-8 packed columns. After the separation of unknown mixtures, the isolated esters are identified from spectroscopic data (IR/NMR) and, after saponification of the ester components (fatty acids and alcohols), from the retention times of gas and high-pressure liquid chromatographic separations. Thus, in particular, sparingly volatile or nonvolatile partial esters of polyhydric alcohols, as well as the long-chained full esters, can be determined qualitatively and quantitatively. The following fatty acid esters of mono- and polyhydric alcohols have been separated: the i-propylesters of the laurinic and myristinic acids, the i-butyl-, i-octyl- and i-octadecyl-esters of the palmitinic and stearic acids, the mono- and di-fatty acid esters of the 1,3-bis-(2-hydroxyethyl)-5,5-dimethylhydantoins, the mono-, di- and tri-esters of the trimethylalpropane and the full esters of the pentaerythrite.     

An unexpected reaction of 2-vinyloxyethyl isothiocyanate with halocarboxylic acids

Reactions of 2-vinyloxyethyl isothiocyanate with aliphatic halocarboxylic acids give rise to their 1-(2-isothiocyanatoethoxy)ethyl esters in quantitative yields. An unusual rearrangement of 1-(2-isothiocyanatoethoxy)ethyl chloro(bromo)acetate and 3-bromopropanoate to 5-aza-7-chloro(bromo)-4-oxo-3-thiaheptanoic and to 6-aza-8-bromo-5-oxo-4-thiaoctanoic acids, respectively, was observed. Monohalocarboxylic acids and their esters were shown to readily alkylate l,3-oxazolidine-2-thione to form the same thiaheptanoic and thiaoctanoic acids and their esters.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 350–354, February, 1993.     

Amino acids and peptides. XXIII. Synthesis of N alpha-protected amino acid 6-chloro-2-pyridyl esters and their evaluation for peptide synthesis

6-Chloro-2-pyridyl esters (OPyCl) of N alpha-benzyloxycarbonyl and tert-butyloxycarbonylamino acids were synthesized by the N,N'-dicyclohexylcarbodiimide (DCC) method from the acids and 6-chloro-2-hydroxypyridine in dimethylformamide (DMF). The reactivity of the 6-chloro-2-pyridylester with amino group is much higher than that of the corresponding 2-pyridyl ester (OPy) and p-nitrophenyl esters (ONp) in dioxane and DMF, and a peptide bond is formed without acylation at the side chain hydroxyl group of amino acids. Z-Asp(OBzl)-OPyCl reacted with amino acid methyl esters in dioxane to give the corresponding dipeptide without any detectable aspartimide formation.     

α-Amidoalkylation of CH-Acids by Means of N-(1,2,2,2-Tetrachloroethyl)-amides

The reaction of α-amidoalkylation of malonic and acetoacetic esters as well as tert. butylacetate, arylacetic acids and benzylcyanide with different N-(1,2,2,2-tetrachloroethyl)-amides was investigated and 2-substituted 3-acylamino-3-trichloromethyl propionic acids and esters were synthezised.     

Analysis of methyl and ethyl esters of hydroxybenzoic and hydroxycinnamic acids in plant material

A method is described for the extraction and purification of methyl and ethyl esters of hydroxybenzoic and hydroxycinnamic acids from plant material. The esters were analyzed as trimethylsilyl derivatives by glass capillary gas chromatography (OV-1, OV-73, Dexsil 300) and gas chromatography-mass spectrometry. The method has been applied to analysis of methyl and ethyl esters of hydroxybenzoic and hydroxycinnamic acids in vegetables and potato peels.     

Method for evaluating the bioconversion of radioactive polyunsaturated fatty acids by use of reversed-phase liquid chromatography

Reversed-phase high-performance liquid chromatography on a thermostatted octadecylsilyl column was used to separate mixtures of labelled polyunsaturated fatty acids (as their methyl esters) formed by successive desaturations and elongations of labelled linoleic (18:2 n - 6) or linolenic (18:3 n - 3) acid by rat liver microsomes. Acetonitrile-water mixtures were used for elution of the esters. Unsaturated and saturated esters were detected by their refractive indices. The order of elution of fatty acid methyl esters in complex mixtures varies as a function of the chain length and unsaturation, analysis temperature, water concentration and solvent flow-rate. The peak areas vary as a function of the unsaturation. Specific radioactivities of 14C-labelled fatty acids and the percentage distribution of radioactivity among fatty acids from complex mixtures can be efficiently determined by collection and direct measurement of the radioactivity in the solvent by liquid scintillation counting. The method can be applied to complete compositional analysis, but is especially useful for determination of specific radioactivities during studies on the metabolic conversion of labelled polyunsaturated fatty acids.     

Optimisation of derivatisation procedures for the determination of delta13C values of amino acids by gas chromatography/combustion/isotope ratio mass spectrometry

Compound-specific stable carbon isotope analysis of amino acids by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) is a highly selective and sensitive method for probing the biosynthetic/diagenetic pathways, pool size and turnover rates of proteins, previously intractable to bulk isotope analyses. However, amino acids are polyfunctional, non-volatile compounds which require derivatisation prior to GC analysis. While a wide range of derivatives exist for the GC analysis of amino acids only a handful have been utilised for their GC/C/IRMS analysis. Significantly, none of those derivatives currently employed appear completely satisfactory and a thorough assessment of their relative utility is lacking. Seven derivatives (three previously reported and four novel) for obtaining delta(13)C values of amino acids via GC/C/IRMS analysis were compared. More specifically, standard mixtures of 15 protein amino acids were converted into N-acetylmethyl (NACME) esters, N-acetyl n-propyl (NANP) esters, N-acetyl i-propyl (NAIP) esters, N-trifluoroacetyl-i-propyl (TFA-IP) esters, N-pivaloyl methyl (NPME) esters, N-pivaloyl n-propyl (NPNP) esters and N-pivaloyl i-propyl (NPIP) esters. Each derivative was assessed with respect to its applicability to carbon isotope determinations of all the common alpha-amino acids, reaction yield, chromatographic resolution, stability, analyte-to-derivative carbon ratio, kinetic isotope effects and errors associated with their carbon isotope determinations. The NACME derivative was concluded to be the preferred derivative mainly due to the highest analyte-to-derivative carbon ratio being achieved, resulting in the lowest analytical errors for amino acid delta(13)C value determinations, ranging from +/-0.6 per thousand for phenylalanine, leucine and isoleucine to +/-1.1 per thousand for serine and glycine.     

Supported liquid membrane separation of amine and amino acid derivatives with chiral esters of phosphoric acids as carriers

Studies on the possible use of phosphate and phosphonate esters bearing chiral menthol or nopol moieties as carriers for the transport of amines, amino acids, and amino acid esters through supported liquid membranes (SLM) are presented. Additionally, the enantioselectivity of the SLM transport of alkyl esters of aromatic amino acids and a non‐protein amino acid was also evaluated. It could be concluded that the extent of transport strongly depends on the hydrophobicity of the amino compound. Moreover, the carrier structure also influences the transport of those compounds through SLM: chiral phosphate and phosphonate esters appear to be poor or moderate carriers for enantioselective SLM transport of amino acids and their esters. The transport efficiency and selectivity is strongly dependent on the structure of both the transported compounds and the carrier. However, no meaningful relationship exists between these structural features and transportation or enantioselectivity.     

A facile synthesis of p- and m-(amidinomethyl)phenyl esters derived from amino acid and tryptic hydrolysis of these synthetic inverse substrates

A facile synthetic method for p- and m-(amidinomethyl)phenyl esters derived from a variety of amino acids is presented. We analyzed the kinetic behavior of trypsin towards these synthetic esters, which are inverse substrates. The substituent (meta- and para-isomers) and isosteric effects of (amidinomethyl)phenyl esters are discussed.     

Facile synthesis of alpha-substituted acrylate esters

Treatment of 5-monosubstituted Meldrum's acids with dimethylmethyleneimmonium iodide (Eschenmoser's iodide salt) in methanol gives alpha-substituted acrylate methyl esters in good yields. Easy access to 5-monosubstituted Meldrum's acids allowed us to synthesize a wide variety of alpha-substituted acrylate methyl esters. The reaction conditions are mild and tolerate many functional groups commonly used in organic synthesis; thus, this new method has potential as an alternative to conventional preparative methods for alpha-substituted acrylate esters.