Addition Of Methoxide Research Articles

Mechanistic Investigations of Phenoxyimine-Cobalt(II)-Catalyzed C(sp2)-C(sp3) Suzuki-Miyaura Cross-Coupling.

The mechanism of phenoxyimine (FI)-cobalt-catalyzed C(sp2)-C(sp3) Suzuki-Miyaura cross-coupling was studied using a combination of kinetic measurements and catalytic and stoichiometric experiments. A series of dimeric (FI)cobalt(II) bromide complexes, [(4-CF3PhFI)CoBr]2, [(4-OMePhFI)CoBr]2, and [(2,6-diiPrPhFI)CoBr]2, were isolated and characterized by 1H and 19F NMR spectroscopies, solution and solid-state magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray crystallography, and diffusion-ordered NMR spectroscopy (DOSY). One complex, [(4-CF3PhFI)CoBr]2, was explored as a single-component precatalyst for C(sp2)-C(sp3) Suzuki-Miyaura cross-coupling. Addition of potassium methoxide to [(4-CF3PhFI)CoBr]2 generated the corresponding (FI)cobalt(II) methoxide complex as determined by 1H and 19F NMR and EPR spectroscopies. These spectroscopic signatures were used to identify this compound as the resting state during catalytic C(sp2)-C(sp3) coupling. Variable time normalization analysis (VTNA) of in situ catalytic 19F NMR spectroscopic data was used to establish an experimental rate law that was first-order in a (FI)cobalt(II) precatalyst, zeroth-order in the alkyl halide, and first-order in an activated potassium methoxide-aryl boronate complex. These findings are consistent with turnover-limiting transmetalation that occurs prior to activation of the alkyl bromide electrophile. The involvement of boronate intermediates in transmetalation was corroborated by Hammett studies of electronically differentiated aryl boronic esters. Together, a cobalt(II)/cobalt(III) catalytic cycle was proposed that proceeds through a "boronate"-type mechanism.

Effect of Calcium Precursor on the Bioactivity and Biocompatibility of Sol-Gel-Derived Glasses.

This study investigated the impact of different calcium reagents on the morphology, composition, bioactivity and biocompatibility of two-component (CaO-SiO2) glasses produced by the Stöber process with respect to their potential application in guided tissue regeneration (GTR) membranes for periodontal repair. The properties of the binary glasses were compared with those of pure silica Stöber particles. The direct addition of calcium chloride (CC), calcium nitrate (CN), calcium methoxide (CM) or calcium ethoxide (CE) at 5 mol % with respect to tetraethyl orthosilicate in the reagent mixture gave rise to textured, micron-sized aggregates rather than monodispersed ~500 nm spheres obtained from the pure silica Stöber synthesis. The broadening of the Si-O-Si band at ~1100 cm−1 in the infrared spectra of the calcium-doped glasses indicated that the silicate network was depolymerised by the incorporation of Ca2+ ions and energy dispersive X-ray analysis revealed that, in all cases, the Ca:Si ratios were significantly lower than the nominal value of 0.05. The distribution of Ca2+ ions was also found to be highly inhomogeneous in the methoxide-derived glass. All samples released soluble silica species on exposure to simulated body fluid, although only calcium-doped glasses exhibited in vitro bioactivity via the formation of hydroxyapatite. The biocompatibilities of model chitosan-glass GTR membranes were assessed using human MG63 osteosarcoma cells and were found to be of the order: CN < pure silica ≈ CC << CM ≈ CE. Calcium nitrate is the most commonly reported precursor for the sol-gel synthesis of bioactive glasses; however, the incomplete removal of nitrate ions during washing compromised the cytocompatibility of the resulting glass. The superior bioactivity and biocompatibility of the alkoxide-derived glasses is attributed to their ease of dissolution and lack of residual toxic anions. Overall, calcium ethoxide was found to be the preferred precursor with respect to extent of calcium-incorporation, homogeneity, bioactivity and biocompatibility.

Synthesis of Fatty Acid Methyl Esters (FAME) from Schizochytrium Marine Microalgae oil

Fatty acid methyl esters (FAME) also called and accepted as biodiesel, obtained prominent importance in this new era as an alternate fuel for petro-diesel. Microalgae are identified as few of such feedstock for the production of biodiesel. Higher volumes of production per hectare area, fast growing ability and high oil contents are the major advantages of microalgae over the conventional oil yielding crops. Schizochytrium is one of marine microalgae and high lipid content of this microalga is ideal for production of biofuels. Also, Schizochytrium oil is found to have 0.1% free fatty acid content which is well within the recommended value for one-step alkaline transesterification. In this work, the synthesis of bio-diesel was carried out from Schizochytrium oil with the addition of potassium methoxide (a mixture of methanol and KOH). Aiming at the higher yield of FAME, essential amounts of methanol, catalyst, and reaction time were optimized. The yielding of FAME was confirmed by Gas Chromatography with Mass Spectroscopy (GC-MS) for each trial of experiment. A conversion efficiency of 99.99% was observed through GC-MS analysis for a 30% v/v methanol, 0.4% w/v KOH and 90 min reaction time at reaction temperature of 60°C. The results were complemented by proton nuclear magneto resonance (1H NMR) spectra and it is found that the synthesized fuel properties are well within the limits of ASTM standards.

Mechanistic Study on Nickel-Catalyzed Silylation of Aryl Methyl Ethers.

The mechanism of the nickel-catalyzed silylation of aryl methyl ethers has been systematically investigated by using DFT methods. This theoretical study supports a catalytic cycle that involves the formation of a nickel-silyl complex, C-O bond cleavage, C-Si reductive elimination, the addition of methoxide to boron, and finally regeneration of the catalyst. Notably, it was found that activation of the C-O bond proceeded through an oxidative addition pathway with a three-centered transition state. The silyl anion generated in situ works as a ligand to the nickel center and promotes this process. Meanwhile, the role of the base added (KOtBu) is also elucidated. The potassium cation helps to stabilize the oxidative addition transition state through noncovalent interactions, while the resting state is destabilized due to steric repulsion introduced by the tert-butoxide anion. This is further confirmed by a comparison made computationally between the reaction with KOtBu and that with KOMe or NaOtBu as the base.

A versatile and efficient approach for the synthesis of chiral 1,3-nitroamines and 1,3-diamines via conjugate addition to new (S,E)-γ-aminated nitroalkenes derived from L-α-amino acids.

New chiral (S,E)-γ-N,N-dibenzylated nitroalkenes 2a–c were synthesized from natural L-(α)-amino acids in five steps with overall yields of 68–88%. The conjugate addition of hydride, methoxide, nitronate and azide nucleophiles to 2a–c led to the corresponding chiral 1,3-nitroamines in 74–90% yield. The conjugate addition of cyanide anion to 2a,b was followed by HNO2 elimination affording chiral aminated acrylonitriles (73–98%). On the other hand, the azide anion reacted with 2a, in acetonitrile, via a [3 + 2]-cycloaddition in which HNO2 was lost, providing the corresponding 1,2,3-triazole derivative. Direct reduction of 1,3-nitroamine derivatives 9a,b produced the corresponding 1,3-diamines in good yields.

Reactions of Copper(II)-Phenol Systems with O2: Models for TPQ Biosynthesis in Copper Amine Oxidases

Copper(II) complexes supported by a series of phenol-containing bis(pyridin-2-ylmethyl)amine N(3) ligands (denoted as L(o)H, L(m)H, and L(p)H) have been synthesized, and their O(2) reactivity has been examined in detail to gain mechanistic insights into the biosynthesis of the TPQ cofactor (2,4,5-trihydroxyphenylalaninequinone, TOPA quinone) in copper-containing amine oxidases. The copper(II) complex of L(o)H (ortho-phenol derivative) involves a direct phenolate to copper(II) coordination and exhibits almost no reactivity toward O(2) at 60 °C in CH(3)OH. On the other hand, the copper(II) complex of L(m)H (meta-phenol derivative), which does not involve direct coordinative interaction between the phenol moiety and the copper(II) ion, reacts with O(2) in the presence of triethylamine as a base to give a methoxy-substituted para-quinone derivative under the same conditions. The product structure has been established by detailed nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, and electrospray ionization-mass spectroscopy (ESI-MS) (including (18)O-labeling experiment) analyses. Density functional theory predicts that the reaction involves (i) intramolecular electron transfer from the deprotonated phenol (phenolate) to copper(II) to generate a copper(I)-phenoxyl radical; (ii) the addition of O(2) to this intermediate, resulting in an end-on copper(II) superoxide; (iii) electrophilic substitution of the phenolic radical to give a copper(II)-alkylperoxo intermediate; (iv) O-O bond cleavage concomitant with a proton migration, giving a para-quinone derivative; and (v) Michael addition of methoxide from copper(II) to the para-quinone ring and subsequent O(2) oxidation. This reaction sequence is similar to that proposed for the biosynthetic pathway leading to the TPQ cofactor in the enzymatic system. The generated para-quinone derivative can act as a turnover catalyst for aerobic oxidation of benzylamine to N-benzylidene benzylamine. Another type of copper(II)-phenol complex with an L(p)H ligand (para-phenol derivative) also reacts with O(2) under the same experimental conditions. However, the product of this reaction is a keto-alcohol derivative, the structure of which is qualitatively different from that of the cofactor. These results unambiguously demonstrate that the steric relationship between the phenol moiety and the supported copper(II) ion is decisive in the conversion of active-site tyrosine residues to the TPQ cofactor.

A Novel Approach to the Evaluation of the Importance of Steric and Electronic Effects in SNAr Reactions: A Computational, Thermodynamic and 1H and 13C NMR Study of “Meisenheimer‐Type” Adducts in the Benzo[b]thiophene Series

AbstractThe synthetically useful nucleophilic attack on nitrobenzo[b]thiophenes, a starting point for ring‐opening/ring‐closure pathways to different heterocyclic systems, has been investigated in detail. 3‐Nitrobenzo[b]thiophene (9) and 2‐nitrobenzo[b]thiophene (10) react with sodium methoxide in either DMSO or methanol to give the relevant “Meisenheimer‐type” adducts 9′ and 10′, identified by NMR spectroscopy. A UV study indicated that the equilibrium constants for the formation of 9′ at 293 K are 10.1 and 40 700 L mol–1 in methanol and in DMSO, respectively. Competition reactions showed that the stability constant of 10′ is lower than that of 9′: accordingly, DFT [B3LYP/6‐31+G(d,p)] calculations indicate that the formation of 9′ is thermodynamically more favoured than that of 10′ both in the gas phase and in DMSO. The reason for the opposite sequence in the stability constants previously found for the corresponding gem‐dimethoxy Meisenheimer adducts 7′ and 8′ was therefore investigated in depth and appears to be a consequence of different steric interactions in the starting compounds, 2‐methoxy‐3‐nitro‐(7) and 3‐methoxy‐2‐nitrobenzo[b]thiophene (8), respectively. A study of 13C NMR chemical shift changes accompanying the formation of adducts 9′ and 10′ confirms that the formation of the adduct exhibiting the larger stability constant is accompanied by a smaller π electron density redistribution, as we have previously found in other cases all governed by electronic effects. The opposite behaviour is observed in the formation of the gem‐dimethoxy adducts 7′ and 8′, which is a consequence of the predominance of steric effects. Further outcomes of more general interest deal with the aromatic character of benzo[b]thiophenes. NMR spectroscopic data and calculated bond lengths show that in the studied reactions the benzene ring, unlike the thiophene one, is scarcely affected by methoxide addition, retaining its nearly “full” aromatic character. Benzocondensation increases the stability constants of σ‐adducts mainly because of a marked reduction in the aromatic character of the thiophene ring in the substrates.

ChemInform Abstract: The Basicity of Alkali Metal Methoxides in Methanol. The Effects of Ion Association on Methoxide Additions to Activated Anisoles.

The formation of adducts with 1 :2 and 1:3 stoichiometry by methoxide addition to nitro-activated anisoles has been examined spectrophotometrically. For these equilibria the ‘basicity’ of sodium methoxide solutions in methanol is appreciably greater than that of corresponding potassium methoxide solutions. This is in contrast with other measures of basicity and is attributed to the association of the multi-charged adducts with cations which is stronger with sodium than with potassium ions.

Novel Syntheses of [6,7,n]-Benzazepinone and [6,6,n]-Benzophenanthridinone Derivatives by Rhodium-catalyzed Cyclization of o-(n-Cyanoalkynyl)benzaldehydes

Since transition metal catalysis allows simultaneous formation of more than one bond in a single step operation with high selectivity, the exploitation of a model compound for nitrogen-containing polycyclic biologically active natural products has been a worthwhile contribution in synthetic and medicinal chemistry. Intramolecular hydroamidation of acetylenes, carbonylation of 2-alkylbenzenylamines, 1-aryl-3-hexen-1,5-diynes initiated by methoxide addition, fluoroarenes and nitriles via 1,2-arynes, nitroarylstannanes, radical dearomatization of benzene and hydrothermal reaction of o-phenylaniline, ullamann cross-coupling of 1-bromo-2-nitroarenes and 1,3dipolarcycloaddition of nonstabilized azomethine ylide and photocycloaddition of phthalimide anion to alkenes have been used to synthesize benzazepinone, phenanthridine and benzophenathridinone derivatives. However, these synthetic routes are often complicated and limited to only some substituents. Recently, we reported various cycloisomerization reactions with different unsaturated systems catalyzed by Au, Pt, Pd, and Rh. Our continued interest in the synthesis of polycyclic systems prompted us to develop the Rhcatalyzed cyclization of o-alkynylbenzaldehydes having a nitrile tether that produced tricyclic benzazepinones and benzophenanthridine derivatives via [3+2] and [4+2] cycloaddition via pyrylium intermediates as shown in Scheme 1. An initial study was tested with o-alkynylbenzaldehyde 1a in the presence of various late transition metal catalysts (Table 1). PtCl2 as a catalyst in refluxing 1,4-dioxane for 12 h converted 1a to give a mixture of products, which were separated by column chromatography to give 2,3-dihydrobenzo[e]cyclopenta[b]azepin-5(1H)-one (3a) in 50% yield along with the hydrated product 2a in 30% yield (entry 1). When this reaction was carried out in dry 1,4-dioxane in the presence of 4 A molecular sieves, the reaction was dramatically accelerated to give the product 3a in 59% yield still along with 2a in 10% yield (entry 2). We presumed that a trace amount of water in the reaction medium or in solvent might generate a nucleophile which could undergo hydration to the metal-activated triple bond followed by tautomerization to the corresponding ketoaldehyde 2a. It was observed that gold(III) bromide in 1,2-dichloroethane (EDC) hydrated 1a to afford 2a even at room temperature exclusively (entry 3). This might be understood by the high reactivity of gold catalyst or the poor reactivity of the nitrile group toward the pyrylium intermediate A. We tried the same reaction with different catalysts, such as AuCl3, AuCl(PPh3) with AgSbF6, and AgSbF6 itself, under dry reaction condtions, but led to hydration (entries 4-6). In fact, Zhu et al. reported that o-alkynylbenzaldehydes were hydrated in the presence of gold(+3) catalysts and trifluoroacetic acid to afford the corresponding ketoaldehyde. Finally, we found [Rh(COD)Cl]2 as an optimal catalyst for the present [3+2] cyclization of pyrylium intermediate, generated in situ with alkynophilic metal cations, with a pendent nitrile. Thus, when the substrate 1a in the presence of [Rh(COD)Cl]2 (10 mol%) in dry xylene containing 4 A molecular sieves was heated at 110 C for 12 h, the product 3a was isolated in 71% yield along with the ketoaldehyde 2a in 10% yield. With this promising result, we further examined this [3+2] cycloaddition with structural alteration in the tether (eq. 1-2). This paper is dedicated to Professor Sang Chul Shim at Kyungpook National University on the occasion of his honorable retirement. Scheme 1 Table 1. Optimization of intramolecular [3 + 2] cyclization-cycloaddition under various reaction conditions with 1a

A New Flavone Glycoside from Zanthoxylum acanthopodium DC.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Characterization of Modified Carbon Nanotubes by TG-MS and Pyrolysis-GC/MS

Abstract Two evolved gas analysis techniques were used to study modified single-wall carbon nanotubes (SWNTs). These techniques were thermogravimetry-mass spectrometry (TG-MS) and pyrolysis-gas chromatography/mass spectrometry (pyrolysis-GC/MS). Increased weight loss was exhibited in the modified SWNTs below 800°C, which was attributed to the addition of methoxide introduced during the modification. The localized environments of the SWNT provide bonding sites of varying strength that results in the staged evolution of the methoxide masses. The continued evolution of methoxide related masses is a result of the variations in the localized environments of the SWNTs, including the curved ends and various other possible sites along the sidewalls. However, once all the modifications have been removed, the overall structure of the SWNT still remains as intact as the pristine sample as indicated by the slope of the weight loss at higher temperatures.

Regioselective Synthesis of Fluoroalkylated β-Aminophosphorus Derivatives and Aziridines from Phosphorylated Oximes and Nucleophilic Reagents

A simple and efficient stereoselective synthesis of fluoroalkyl substituted aziridine-2-phosphine oxides and -phosphonates by diastereoselective addition of methoxide, imidazole, benzenethiol, and Grignard reagents to functionalized ketoxime-phosphine oxides and -phosphonates is described. Aziridines are used as intermediates for the regioselective synthesis of fluorine containing beta-amino phosphine oxides and beta-amino phosphonates. Amino phosphorus derivatives can also be obtained from ketoximes derived from phosphine oxides and phosphonates with sodium borohydride.

Synthesis of (Vinylidene)‐ and (Cyclopropenyl)ruthenium Complexes Containing a Tris(pyrazolyl)borato (Tp) Ligand

AbstractA convenient high‐yield route to [Ru(C≡C−Ph)(Tp)(PPh3)2] [2; Tp = HB(pz)3, pz = pyrazolyl] has been found through the intermediacy of [RuCl2(Hpz)2(PPh3)2] (1). This complex is readily obtained on treatment of [RuCl2(PPh3)3] with 2 equiv. of pyrazole in boiling THF. The molecular structures of complexes 1 and 2 have been confirmed by single‐crystal X‐ray diffraction analysis. A number of new cationic vinylidene complexes [Ru{=C=C(Ph)CH2R}(Tp)(PPh3)2]+ [3a, R = CN; 3b, R = HC=CH2; 3c, R = CH=C(CH3)2; 3d, R = Ph; 3e, R = C(O)OMe] have been prepared by electrophilic addition of organic halides to complex 2. The deprotonation reaction of 3a yields the cyclopropenyl complex 4a. One phosphane ligand of 4a is remarkably labile, being replaced by donor ligands L to yield diastereomeric mixtures of the cyclopropenyl complexes 5a−5d mostly in an approximate 4:1 ratio. The cyclopropenyl rings in 4a and 5a are susceptible to ring opening by I2. In addition, treatment of 4a with nBuNC in the presence of MeOH results in substitution of a phosphane ligand by nBuNC followed by protonation of the three‐membered ring by MeOH. This is then followed by addition of methoxide to give the vinyl ether complex [Ru{C(OMe)=C(Ph)CH2CN}(Tp)(PPh3)(nBuNC)] (8a). (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)

Concave reagents: Part 40—The copper(II) complex of a concave reagent as a selective catalyst for ester methanolysis

AbstractWe have shown that the CuII complexes of the concave ligand 1 and its model compound 2 are efficient catalysts of ester methanolysis under conditions close to neutrality. Turnover catalysis without product inhibition was demonstrated by the clean first‐order release of a greater than stoichiometric amount of product. Compared with background methanolysis, the metal catalysts give greater rate accelerations for methyl acetate methanolysis than for the p‐nitrophenyl acetate methanolysis.Analysis of electronic and steric effects on rates of metal‐mediated vs metal‐free methoxide addition to the esters has provided compelling evidence that transfer of methoxide from the metal to the carbonyl carbon is accompanied by extensive Lewis acid activation of the carbonyl via a four‐membered chelate transition state that includes the metal ion. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Anionic Cycloaromatization of 1‐Aryl‐3‐hexen‐1,5‐diynes. Initiated by Methoxide Addition: Synthesis of Phenanthridinones, Benzo[c]phenanthridinones, and Biaryls.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Anionic cycloaromatization of 1-aryl-3-hexen-1,5-diynes initiated by methoxide addition: synthesis of phenanthridinones, benzo[c]phenanthridinones, and biaryls.

Treatment of 2-((Z)-6-substituted-3-hexene-1,5-diynyl)benzonitriles with sodium methoxide in refluxing methanol in the presence of a polar aprotic solvent, such as DMSO, HMPA, THF, or 18-crown-6, gave phenanthridinones in 21-77% yields. In these cases, addition of 10% DMSO into the reaction mixture gave the highest yield. On the other hand, methanolysis of 2-(2-(2-alkynylphenyl)ethynyl)benzonitriles under the same reaction conditions gave benzo[c]phenanthridinones in 31-57% yields. Methanolysis of (Z)-1-aryl-3-hexen-1,5-diynes in the presence of 2 equiv of tetrabutylammonium iodide gave biaryls in 14-64% yields. It is found that the reactions with aryl groups bearing electron-withdrawing groups proceeded at greater rates and gave better yields.

Synthesis of Highly Functionalized Amino Acid and Hydroxy Acid Derivatives from γ‐Aminoalkyl‐Substituted α‐Methylene‐γ‐butyrolactones

Addition of C-, S-, N- and O-nucleophiles to α-amino acid derived α-methylene-γ-butyrolactones provided the corresponding Michael adducts. Addition of cuprates or cyanide, respectively, could be achieved with excellent selectivities. Addition of malonate anion or methoxide could be performed with good yields, but with rather poor selectivities. Addition of N-nucleophiles was achieved with N-benzylhydroxylamine. Further reductive cleavage of the hydroxy and the benzyl groups under hydrogenolytic conditions afforded a diaminocarboxylic acid derivative. Addition of S-nucleophiles furnished the corresponding 1,4 adducts in excellent yields and with good selectivities, especially when a cysteine derivative was used as nucleophile. Hydrogenation of the α-methylene-γ-butyrolactones provided α-methyl-substituted lactones, and ozonolysis yielded the corresponding α,β-dicarbonyl compounds. An isomerization of the exocyclic double bond to an endocyclic double bond was achieved with rhodium chloride as catalyst. The configurations of all products were established by X-ray crystallographic analyses and NMR spectroscopy, including NOE experiments.

Verdoheme reactivity. Remarkable paramagnetically shifted (1)H NMR spectra of intermediates from the addition of hydroxide or methoxide with Fe(II) and Fe(III) verdohemes.

Studies of the reaction of 5-oxaporphyrin iron complexes (verdohemes) with methoxide ion or hydroxide ion have been undertaken to understand the initial step of ring opening of verdohemes. High-spin [ClFe(III)(OEOP)] undergoes a complex series of reactions upon treatment with hydroxide ion in chloroform, and similar species are also detected in dichloromethane, acetonitrile, and dimethyl sulfoxide. Three distinct paramagnetic intermediates have been identified by (1)H NMR spectroscopy. These reactive species are formed by addition of hydroxide to the macrocycle and to the iron as an axial ligand. Treatment of low-spin [(py)(2)Fe(II)(OEOP)]Cl (OEOP is the monoanion of octaethyl-5-oxaporphyrin) with excess methoxide ion in pyridine solution produces [(py)(n)()Fe(II)(OEBOMe)] (n = 1 or 2) ((OEBOMe), dianion of octaethylmethoxybiliverdin), whose (1)H NMR spectrum undergoes marked alteration upon addition of further amounts of methoxide ion. An identical (1)H NMR spectrum, which is characterized by methylene resonances with both upfield and downfield paramagnetic shifts, is formed upon treatment of [Fe(II)(OEBOMe)](2) with methoxide in pyridine solution and results from the formation of [(MeO)Fe(II)(OEBOMe)](-).

Toward an artifical acetylcholinesterase.

The methanolysis of choline p-nitrophenylcarbonate in chloroform containing 1% methanol is catalyzed with turnover by ditopic receptors 1 and 2, consisting of a calix[6]arene connected to a bicyclic guanidinium by means of a short spacer. The calix[6]arene subunit strongly binds to the trimethylammonium head group through cation-pi interactions, whereas the guanidinium moiety is deputed to stabilize through hydrogen bonding reinforced by electrostatic attraction the anionic tetrahedral intermediate resulting from methoxide addition to the ester carbonyl. The observed cholinesterase activity had been anticipated on the basis of the ability of the ditopic receptors 1 and 2 to bind strongly to the choline phosphate DOPC, which is a transition state analogue for the BAc2-type cleavage of choline esters.

Determination of Lipids in Infant Formula Powder by Direct Extraction Methylation of Lipids and Fatty Acid Methyl Esters (FAME) Analysis by Gas Chromatography

Fatty acid methyl esters (FAMEs) of pure triglyceride standards, oils, and fat from dry matrixes were formed by transesterification using sodium methoxide in methanol-hexane. FAMEs were produced by direct addition of sodium methoxide-hexane to samples and heating to simultaneously extract and transesterify acyl lipids. FAMEs were quantitated by capillary gas chromatography (GC) over a fatty acid concentration range of 0 to 1.7 mg/mL (r > or = 0.9997). Total fat was calculated as the sum of individual fatty acids expressed as triglyceride equivalents, in accordance with nutrition labeling guidelines. Saturated, polyunsaturated, and monounsaturated fats were calculated as sums of individual free fatty acids. Absolute recoveries determined from individual fatty acids in test samples ranged from 69.7 to 106%. Recoveries (relative to the C13:0 internal standard) for individual fatty acids in test samples ranged from 95 to 106%. Reproducibility was constant at each fatty acid level in the reaction mixture (n = 5, coefficient of variation [CV] < 2%). Absolute recovery determined from the sum of total fatty acids in standard reference material (SRM) 1846 (powdered infant formula) was 96.4%. Analysis of SRM 1846 gave results that agreed closely with the certified fat and fatty acid values. Analysis of commercial infant formula gave results that were comparable to those obtained with AOAC Method 996.01. The direct extraction methylation procedure is rapid, and the transesterification of acyl lipids to form FAMEs is complete within 15 min. Classical saponification and refluxing are not required. This method provides FAMEs free of interferences and easily quantitated by GC or confirmed by GC/mass spectrometry (MS). Unambiguous MS identification of individual FAMEs derived from pure standards, SRM 1846, and powdered infant formula product was obtained.