Concurrent esterification and N-acetylation of amino acids with orthoesters: A useful reaction with interesting mechanistic implications

The concurrent esterification and N-acetylation of amino acids has been studied with triethyl orthoacetate (TEOA) and triethyl orthoformate (TEOF). In a surprising finding, only 1 equiv of TEOA in refluxing toluene was necessary to convert l-proline and l-phenylalanine into the corresponding N-acetyl ethyl esters in good yield. The same transformation using TEOF was not effective. Stereochemical outcome and stoichiometric studies as well as structural variation of the amino acids in this reaction provided unexpected mechanistic insight.     

Trimethyl Orthoacetate and Ethylene Glycol Mono‐Vinyl Ether as Enolate Surrogates in Enantioselective Iridium‐Catalyzed Allylation

Trimethyl orthoacetate and ethylene glycol mono‐vinyl ether are employed in iridium‐catalyzed enantioselective allylation reactions. The method documented enables their convenient use as surrogates for silyl ketene acetals and silyl enol ethers to prepare γ,δ‐unsaturated esters and protected aldehydes with excellent enantioselectivity. The utility of this novel method has been demonstrated by its implementation in a formal enantioselective synthesis of the meroterpenoid (+)‐conicol.     

Synthesis of Derivatives of 1,3,4-Oxadiazoles Based on Monohydrazides of 2-Aryl-4-methyl-4-cyclohexen-1,2-dicarboxylic Acids

The corresponding derivatives of 1,3,4-oxadiazoles have been synthesized by the reaction of monohydrazides of 2-aryl-4-methyl-4-cyclohexen-1,1-dicarboxylic acids with triethyl orthoformate or triethyl orthoacetate.     

Simultaneous analysis of biologically active aminoalkanephosphonic acids

A new approach for simultaneous analysis of biologically active aminoalkanephosphonic acids, namely glyphosate, phosphonoglycine, phosphonosarcosine, phosphonoalanine, phosphono-beta-alanine, phosphonohomoalanine, phosphono-gamma-homoalanine and glufosinate, is presented. This includes a preliminary 31p NMR analysis of these amino acids, their further derivatization to volatile phosphonates (phosphinates) by means of trifluoroacetic acid-trifluoroacetic anhydride-trimethyl orthoacetate reagent and subsequent analysis of derivatization products using MS and/or GC-MS (chemical ionization and/or electron impact ionization).     

蔗糖分子中羟基的选择性保护的研究

蔗糖和原乙酸三烷基酯反应后,经三苯甲基化、乙酰化以及乙酰基由4-位到6-位的基团迁移反应,选择性地保护了蔗糖分子中的羟基基团,合成了一系列蔗糖乙酸酯.4,6-原乙酸蔗糖六乙酸酯在酸催化下水解和醇解,相应地得到2,3,6,1',3',4',6'-七-O-乙酰基蔗糖和2,3,1',3',4',6'-六-O-乙酰基蔗糖。这些都是合成蔗糖衍生物方便的中间体,在糖化学的研究中得到应用.     

One-pot esterification and amidation of phenolic acids

We developed a new one-pot reaction of phenolic acids to afford the corresponding esters and amides through acyl-protected and activated phenolic acid intermediates. The simultaneous protection/activation of phenolic acids with alkylchloroformates proceeded readily in the presence of DMAP at room temperature; subsequent addition of alcohols or amines afforded the corresponding esters or amides. The use of iso-butyloxycarbonyl as the protecting and activating group in the one-pot reactions afforded phenolic esters or amides in 91% average yield. As a practical example of this convenient synthesis, caffeic acid phenethyl ester (CAPE) was readily synthesized from commercially available caffeic acid and phenethyl alcohol in 95% yield, and an isotopomer of CAPE, [3,10-¹³C₂]CAPE, was synthesized in 91% yield from [3-¹³C]caffeic acid and 2-[1-¹³C]phenethyl alcohol. This method may be useful for the convenient esterification and amidation of diverse phenolic acids.     

Correlation between structure and stability of nitronic acids and nitronic esters

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Unnatural amino acids. 3. Aziridinyl ketones from esters and amides of aziridine-2-carboxylic acids

A series of N-substituted amides and esters of aziridine-2-carboxylic acids have been prepared and have been subjected to deprotonation with lithium diisopropylamide. The intermediate carbanions reacted more readily with the carbonyl groups of the substrates than with methyl iodide. So, in place of the expected amides or esters of methylaziridine-2-carboxylic acids, amides or esters of 2-aziridinylcarbonylaziridine-2-carboxylic acids were isolated. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, 220–225, February, 2007.     

Metal-free synthesis of aryl esters by coupling aryl carboxylic acids and aryl boronic acids

A facile synthesis of aryl esters is developed by coupling aryl carboxylic acids and aryl boronic acids in the presence of PhI(OAc)₂ and carbonyl diimidazole. A wide range of functional groups were tolerant to the metal-free reaction condition that led to the desired products in good yields.     

Homocoupling of arylboronic acids catalyzed by simple gold salts

A range of arylboronic acids undergo a homocoupling reaction in the presence of catalytic amount of gold salts to yield symmetrical biaryls. Alkenylboronic acids, arylboronic esters, and arylborates also participate in the gold-catalyzed homocoupling reaction.     

Determination of particulate fatty acids as P-bromophenacyl- or phenylphenacylesters using HPLC

Summary A method for the determination of fatty acids of the molecular weight range of propionic to erucic acid is reported. The acids are converted to either p-bromophenacyl-or p-phenylphenacylesters and the esters are separated by HPLC and detected by UV-absorption. Twentytwo esters, including saturated, monoolefinic and polyunsaturated ones were separated within one HPLC-run. The detection limit is about 5 pmol per fatty acid. The application of the method to particulate material is described.     

Thermal degradation behavior of cellulose fibers partially esterified with some long chain organic acids

The thermal degradation behavior of cellulose fibers and some fibrous cellulose esters with partial degree of substitution has been studied by thermogravimetry analysis (TG) and differential scanning calorimetry (DSC). Cellulose esters were prepared by heterogeneous esterification in Py/TsCl with unsaturated or saturated long chain organic acids [undecylenic (C₁₁), undecanoic (C₁₁), oleic (C₁₈) and stearic (C₁₈)]. The thermal degradation of cellulose fibers follows a one-step process. The thermal stability of cellulose esters is inferior to that of unmodified cellulose fibers and the thermograms show a two-step degradation process, probably controlled by crosslinking reactions, which occur during thermal decomposition. Exothermic peaks in the DSC thermograms are also an indication of such reactions. Kinetic parameters such as the activation energy E, order of decomposition n, and frequency factor Z were obtained following the Friedman method. The cellulose sample followed first order of decomposition, however for cellulose esters higher orders were observed.     

Rapid isolation of omega‐3 long‐chain polyunsaturated fatty acids using monolithic high performance liquid chromatography columns

Eicosapentaenoic and docosahexaenoic acids are important bio‐active fatty acids in fish oils. Monolithic HPLC columns both in the polymeric cation exchange (silver‐ion) and RP formats were compared with corresponding packed columns for the isolation of these acids from tuna oil ethyl esters. Monolithic columns in both formats enabled rapid (typically 5–10 min) separations compared with packed columns (30 min). Polymeric monolithic silver‐ion disc column rapidly furnished mixtures of eicosapentaenoic and docosahexaenoic esters (90% purity) within 5–10 min, but was unable to resolve individual esters. A preparative version of the same column (80 mL bed volume) enabled isolation (>88% purity) of 100 mg quantities of eicosapentaenoic and docosahexaenoic esters from esterified tuna oil within 6 min. Baseline separation of eicosapentaenoic and docosahexaenoic esters was achieved on all RP columns. The results show that there is potential to use polymeric monolithic cation exchange columns for scaled‐up preparation of eicosapentaenoic and docosahexaenoic ester concentrates from fish oils.     

Efficient photolytic esterification of carboxylic acids with alcohols in perhalogenated methane

Condensation of carboxylic acids and alcohols to give esters was accomplished with selectivity under photolytic conditions in 66-99% yields by use of CCl₄ or BrCCl₃ at room temperature.     

Rapid analysis of free medium-chain fatty acids and related ethyl esters in beer using SPE and HRGC

A modification of a procedure by Hage [1] is proposed for the gas chromatographic evaluation of the content of free medium-chain fatty acids and related ethyl esters in beer. The method involves extraction of free fatty acids and ethyl esters by SPE using C₁₈ bonded phase columns, derivatization of free fatty acids and related ethyl esters with diazomethane, and GC analysis using an SP-2340 capillary column. The results obtained have shown the method to be rapid and highly reproducible. The technique has been compared with other methods used for determination of free fatty acids.     

Synthesis of N-phosphoryl amino acids using bis(9-fluorenylmethyl)phosphite

Bis(9-fluorenylmethyl)phosphite (BFMP) was found to be an effective reagent for the N-phosphorylation of various amino acid methyl esters. BFMP was prepared from N,N-diisopropyl phosphoramidous dichloride in a one-pot two-step reaction and was obtained as a crystalline solid. N-Phosphorylation of the methyl esters of seven representative amino acids with BFMP was high-yielding and generally resulted in crystalline products. Complete deprotection of both the 9-fluorenylmethylphosphosphate esters and the amino acid methyl esters was accomplished concomitantly with LiOH to give N-phosphoryl amino acids.     

Morpholinization of aminoacyloxy acids and hydroxyacylamino acids and their esters under mass spectrometry conditions

Summary 1. Free hydroxyacylamino acids and their methyl esters, and also free aminoacyloxy acids, morpholinize under mass spectrometry conditions.2. In the mass spectrometry of methyl esters of aminoacyloxy acids and tert-butyl esters of aminoacyloxy acids and hydroxyacylamino acids no morpholinization takes place. These compounds behave similarly to the esters of acylated peptides and depsipetides.Khimiya Prirodnykh Soedinenii, Vol. 3, No. 5, pp. 325–327, 1967     

An effective kinetic resolution of racemic α-arylpropanoic acids, α-arylbutanoic acids, and β-substituted-α-arylpropanoic acids with bis(9-phenanthryl)methanol as a new achiral nucleophile in the asymmetric esterification using carboxylic anhydrides and the acyl-transfer catalyst

A general method for the kinetic resolution of racemic α-arylalkanoic acids with achiral alcohols is described. It was determined that bis(9-phenanthryl)methanol is a suitable nucleophile which reacts with the intermediary mixed anhydrides generated from aromatic anhydrides with α-arylpropanoic acids or β-substituted-α-arylpropanoic acids in the presence of (+)-benzotetramisole to produce the corresponding optically active esters with high ee’s under very mild conditions.     

Activated esters of substituted pyrazinecarboxylic acids

N-Amidino-3,5-diamino-6-chloropyrazinecarboxamide ( 1 ) has been shown to be an effective potassium sparing diuretic. Various carboxyl activating agents have been employed with 3-amino-pyrazinecarboxylic acids in an effort to synthesize analogs of 1. Stable enol esters were isolated from a number of such acids and N-t-butyl-5-methylisoxazolium perchlorate ( 12 ). Although strong bases in DMF or DMSO catalyze a competing destruction of the enol ester system, these esters are useful acylating agents for a variety of nucleophilic substrates in less polar media. Amides, esters, and thiol esters are produced in good yields under mild conditions from these activated esters.     

Capillary gas chromatographic analysis of amino acids in geological environments with electron capture detection

Studies have been performed on the analysis of 21 amino acids using a fused-silica open tubular (FSOT) capillary column, and electron-capture detection (ECD) or flame-ionization detection (FID). It was shown with the N(O)-heptafluorobutyryl (HFB) amino acid isobutyl esters that the ECD response was several hundred times more sensitive than the FID response. The relative standard deviation (RSD) of retention relative to norleucine is determined with the ECD. RSD values for all N(O)-HFB amino acid isobutyl esters are relatively small (≦ 0.5%). This method has been successfully applied to trace analysis of most of the amino acids from fossil brachiopods and black shales.