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PubMed1989

Synthesis of buffers for generating immobilized pH gradients. II: Basic acrylamido buffers.

Six basic acrylamido buffers, for isoelectric focusing in immobilized pH gradients, are described: a strong titrant (pK greater than 12), QAE-acrylamide, and five weaker bases, namely: 2-morpholinoethyl acrylamide (pK 6.2), 3-morpholinopropyl acrylamide (pK 7.0), N,N-dimethyl aminoethyl acrylamide (pK 8.5), N,N-dimethyl aminopropyl acrylamide (pK 9.3) and N,N-diethyl aminopropyl acrylamide (pK 10.3). Their synthesis and general properties are described.

Acrylamides↗
PubMed1990

Anomalously slow electrophoretic mobilities of DNA restriction fragments in polyacrylamide gels are not eliminated by increasing the gel pore size.

The effect of gel pore size on the anomalous mobility of certain curved DNA restriction fragments in polyacrylamide gels was studied by comparing the electrophoretic mobilities of normal and anomalous fragments in gels of varying composition but constant acrylamide concentration. Molecular weight ladders were prepared from two 147 base pair G-C rich restriction fragments, called 12A (anomalous) and 12B (normal), obtained from the MspI digestion of plasmid pBR322. The electrophoretic mobilities of multimers of the two fragments increasingly diverged with increasing molecular weight. The anomalous mobility of fragment 12A was essentially independent of gel pore size, regardless of whether the pore size was varied by increasing the acrylamide concentration at constant cross-linker concentration or by increasing the cross-linker concentration at constant acrylamide concentration. The anomalous mobility of higher multimers of fragment 12A decreased with increasing gel pore size when the pore size was varied by changing the gel concentration. However, when the gel pore size was changed by varying the cross-linker concentration at constant acrylamide concentration, the anomalous mobility of higher multimers of fragment 12A went through a maximum and then decreased as the pore size was increased. Copolymerizing acrylamide with high molecular weight linear polyacrylamides had no effect on the anomalous mobility of the 12A multimer ladder, even though the apparent absolute mobilities of all fragments increased markedly. Only by incorporating charged residues into the gel matrix or by copolymerizing acrylamide with the intercalator ethidium bromide could the difference in mobility between the 12A and 12B multimer ladders be substantially reduced or eliminated. Similar results were observed with a molecular weight ladder containing 78 base pair repeats of the bending locus of kinetoplast DNA. These results suggest that pore size alone is not responsible for the anomalously slow migration of curved DNA molecules in polyacrylamide gels.

Base Sequence↗
PubMed2005

Quantification of urinary N-acetyl-S- (propionamide)cysteine using an on-line clean-up system coupled with liquid chromatography/tandem mass spectrometry.

Acrylamide has been reported to be present in high-temperature processed foods and normal processed food intake could lead to significant acrylamide exposure. Acrylamide in vivo can be conjugated with glutathione in the presence of glutathione transferase. This conjugation product is further metabolized and excreted as N-acetyl-S-(propionamide)cysteine (NASPC) in the urine. NASPC could be considered a biomarker for acrylamide exposure. The objective of this study was to develop a highly specific, rapid and sensitive method to quantify urinary NASPC, serving as a biomarker for acrylamide exposure assessment. Isotope-labeled [13C3]NASPC was successfully synthesized and used as an internal standard. This urine mixture was directly analyzed using a newly developed liquid chromatographic/tandem mass spectrometric method coupled with an on-line clean-up system. The detection limit for this method was estimated as < 5 microg l(-1)(0.4 pmol) on-column. The method was applied to measure the urinary level of NASPC in 70 apparently health subjects. The results showed that the NASPC urinary level was highly associated with smoking. Smokers had a significantly higher urinary NASPC level (135 +/- 88 microg g(-1) creatinine) than non-smokers (76 +/- 30 microg g(-1) creatinine). A highly sensitive and selective LC/MS/MS isotope dilution method was successfully established. With an on-line clean-up system, this system is capable of routine high-throughput analysis and accurate quantitation of NASPC in urine. This could be a useful tool for health surveillance for acrylamide exposure in a population for future study.

Acetylcysteine↗
PubMed1991

Cell behaviour on polymer surfaces grafted with non-ionic and ionic monomers.

Following exposure to corona discharge, a polyethylene film was graft polymerized with different water-soluble monomers such as acrylamide (non-ionic), acrylic acid (anionic), 2-acrylamide-2-methyl propane sulphonic acid (anionic), styrene sulphonic acid sodium salt (anionic) and N,N-dimethylaminopropyl acrylamide (cationic). Attachment and proliferation of HeLa S3 cells were studied for grafted surfaces with different zeta potentials and contact angles. The polyethylene surface graft polymerized with styrene sulphonic acid sodium salt exhibited high cell attachment and protein adsorption, whereas the cells did not adhere to the 2-acrylamide-2-methyl propane sulphonic acid graft-polymerized surface, although both surfaces had high negative zeta potentials. Graft polymerization of acrylamide reduced the zeta potential of surface close to zero and rejected the cell attachment. The polyethylene surface became highly cell-adhesive through graft polymerization of the cationic N,N-dimethylaminopropyl acrylamide monomer, but too much grafting killed the attaching cells. Once the cells attached to a surface without being killed, they could proliferate at the same growth rate, whatever their surface zeta potential.

Acrylic Resins↗
PubMed2001

Tyrosine kinase inhibitors. 18. 6-Substituted 4-anilinoquinazolines and 4-anilinopyrido[3,4-d]pyrimidines as soluble, irreversible inhibitors of the epidermal growth factor receptor.

4-Anilinoquinazoline- and 4-anilinopyrido[3,4-d]pyrimidine-6-acrylamides are potent pan-erbB tyrosine kinase inactivators, and one example (CI-1033) is in clinical trial. A series of analogues with a variety of Michael acceptor units at the 6-position were prepared to define the structural requirements for irreversible inhibition. A particular goal was to determine whether additional functions to increase solubility could be appended to the Michael acceptor. Substituted acrylamides were prepared by direct acylation of the corresponding 6-amines with the requisite acid or acid chloride. Vinylsulfonamide derivatives were obtained by acylation of the amines with chloroethylsulfonyl chloride followed by base-promoted elimination. Vinylsulfone and vinylsulfine derivatives were prepared by oxidation and base elimination of a hydroxyethylthio intermediate. The compounds were evaluated for their inhibition of phosphorylation of the isolated EGFR enzyme and for inhibition of EGF-stimulated autophosphorylation of EGFR in A431 cells and of heregulin-stimulated autophosphorylation of erbB2 in MDA-MB 453 cells. Substitution at the nitrogen of the acrylamide was tolerated only with a methyl group; larger substituents were dystherapeutic, and no substitution at all was tolerated at the acrylamide alpha-carbon. In contrast, while electron-donating groups at the acrylamide beta-carbon were not useful, even quite large electron-withdrawing groups (which increase its electrophilicity) were tolerated. A series of derivatives with solubility-enhancing substituents linked to the acrylamide beta-carbon via amides were potent irreversible inhibitors of isolated EGFR (IC50s = 0.4-1.1 nM), with weakly basic morpholine and imidazole derivatives being the best. Vinylsulfonamides were also potent and irreversible inhibitors, but vinylsulfones and vinylsulfines were reversible and only poorly active. Two compounds were evaluated against A431, H125, and MCF-7 xenografts in nude mice but were inferior in these assays to the clinical trial compound CI-1033.

Animals↗
PubMedDate not supplied

A fluorescence double-quenching study of native lipoproteins in an animal model of manganese deficiency.

Iodide and acrylamide were applied simultaneously in a double-quenching experiment to compare acrylamide quenching constants for internal and external fluorophores of high-density lipoproteins (HDL1 and HDL2) from manganese-adequate (MnA) and deficient (MnD) rats, free of the electrostatic effects associated with iodide. In MnA HDL1 compared to MnD HDL1, the acrylamide quenching constant for external fluorophores was different (P < 0.1). In MnA HDL2, there were two populations of fluorophores accessible to acrylamide, whereas in MnD HDL2, all fluorophores were accessible to both quenchers. We concluded that there were structural (local environmental) differences, possibly charge-related, around the external fluorophores, and a slightly larger population of buried fluorophores in the MnD HDL1 compared with MnA HDL1. In MnA HDL2, one-third of the fluorophores were accessible to iodide, and all external and internal fluorophores were accessible to acrylamide, whereas in MnD HDL2, all fluorophores were accessible to both quenchers.

Acrylamide↗
PubMed1996

Effect of vitamin B complex on neurotransmission and neurite outgrowth.

1. The effect of vitamin B complex (vitamin B1, B6 and B12) was studied on nerve conduction velocity in acrylamide-neuropathy rats maintained on refined semisynthetic complete vitamin and vitamin B-deficient diets in vivo and on neurite outgrowth in vitro using cells obtained from dorsal root ganglions of mice. 2. Acrylamide neuropathy was clearer in the group maintained on a refined semisynthetic vitamin B-deficient diet than in those on a refined semisynthetic complete vitamin diet. The neurotoxicity was lowest in the group given vitamin B complex prophylactic-therapeutically, next higher following therapeutic administration and last with no vitamin B complex administration in both groups maintained on a refined semisynthetic vitamin B-deficient diet and a refined semisynthetic complete vitamin diet. 3. The nerve conduction velocity tended to decrease by treatment with acrylamide. The decrement of nerve conduction velocity was partially inhibited by vitamin B complex. No significant difference was found in the groups treated with acrylamide and given vitamin B complex prophylactic-therapeutically and the control (no acrylamide treatment) in the group maintained on a refined semisynthetic vitamin B-deficient diet. 4. The greatest neurite outgrowth was found in the group treated with vitamins B1, B6 and B12-enriched medium, followed by the group of vitamin B12-enriched and vitamin B1-enriched media. All groups treated with a vitamin B-enriched medium had significantly greater (P < 0.01) outgrowth than the controls.

Acrylamide↗
PubMed1999

Investigation of some covalent and noncovalent complexes by matrix-assisted laser desorption/ionization time-of-flight and electrospray mass spectrometry.

Covalent and noncovalent complexes involving bovine superoxide dismutase, bovine alpha-lactalbumin and two variants, A and B, of bovine beta-lactoglobulin have been examined by delayed extraction matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray mass spectrometry. Covalent complexation with acrylamide was obtained through the interaction of these proteins with acrylamide monomers while treatment with peroxynitrite yielded complexes with NO2. Some of the complexation sites with acrylamide were reliably identified by performing tryptic digestion followed by MALDI-TOF measurements in the reflection mode. These data demonstrate that the presence of free cysteine in the investigated sequences is not a precondition for the observation of Cys-acrylamide complexes. Although the bulk of the present work is dedicated to the characterization of Cys-acrylamide adducts, the preliminary data on noncovalent complexes between two of those proteins and 8-anilinonaphthalene-1-sulfonic acid (ANS) were easily observed under electrospray conditions, while under MALDI-TOF conditions only the complex with beta-lactoglobulin B was clearly evident. The presented data demonstrate the advantage of the parallel use of both ionization techniques for this type of investigation.

Acrylamide↗
PubMed1993

Effects of neurotoxins on brain creatine kinase activity.

The effects of ethylene oxide (EO), acrylamide, N,N'-methylene-bis-acrylamide (bis-acrylamide), and methyl mercury chloride (MMC) on brain creatine kinase (CK) activity were examined in vivo. EO and acrylamide, both of which cause central-peripheral distal axonopathy, inhibited CK activity in the brain and spinal cord. On the other hand, neither bis-acrylamide, a nonneurotoxic analogue, nor MMC which causes neuronopathy affected brain CK activity significantly. The inhibition of CK may play a role in the pathogenesis of distal axonal degeneration in the central and peripheral nervous systems.

Acrylamides↗
PubMed2005

Models of protein modification in Tris-glycine and neutral pH Bis-Tris gels during electrophoresis: effect of gel pH.

The pH of conventional Tris-glycine SDS-PAGE gels during a run is determined to be 9.5, in contrast to Bis-Tris-Mes gels where the pH is 7.2. Concentrations of free acrylamide are determined to be less than 10mM in commercial gels of both types, and it is found that of the major components in these gels, only glycine and protein amine or sulfhydryl functions are likely to react with residual acrylamide during the time frame of typical separations. The addition of acrylamide to sulfhydryl groups on proteins is modeled using glutathione and cysteine at acrylamide concentrations found in the commercial gels. Rate constants are determined for these reactions as well as for reaction with glycine at the pH that proteins will encounter in these gel types. The half-life for glutathione sulfhydryl at 10mM acrylamide and pH 7.2 is more than 4h at room temperature. Rates are significantly lower in Bis-Tris-Mes gels than in Tris-glycine gels, reducing the risk of adventitious protein modification. Commercial Bis-Tris-Mes gels provide a sample reduction buffer at pH 8.5 versus the conventional pH 6.8 of Tris-glycine gels. It is shown that significantly less protein degradation occurs during sample preparation at the higher pH used with Bis-Tris gels.

Acrylamide↗
PubMed1998

Modification of cysteine residues by alkylation. A tool in peptide mapping and protein identification.

Although mass spectrometric peptide mapping has become an established technique for the rapid identification of proteins isolated by polyacrylamide gel electrophoresis (PAGE), the results of the identification procedure can sometimes be ambiguous. Such ambiguities become increasingly prevalent for proteins isolated as mixtures or when only very small amounts of the proteins are isolated. The quality of the identification procedure can be improved by increasing the number of peptides that are extracted from the gel. Here we show that cysteine alkylation is required to ensure maximal coverage in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) peptide mapping of proteins isolated by PAGE. In the described procedure, alkylation was performed prior to electrophoresis to avoid the adventitious formation of acrylamide adducts during electrophoresis. In this way, homogeneous alkylation was obtained with three different alkylating reagents (4-vinylpyridine, iodoacetamide, acrylamide). Cysteine alkylation was also used as a tool for the identification of cysteine-containing peptides. Using a 1:1 mixture of unlabeled acrylamide and deuterium-labeled acrylamide ([2,3,3'-D3]acrylamide), the proteins of interest were alkylated prior to electrophoretic separation. Peptide mixtures produced by trypsin digestion of the resulting protein bands were analyzed by MALDI-TOF MS, and the cysteine content of the peptides was inferred from the isotopic distributions. The cysteine content information was readily obtained and used to improve the protein identification process.

Acrylamide↗
PubMed2004

Estimates of lifetime-absorbed daily doses from the use of personal-care products containing polyacrylamide: a Monte Carlo analysis.

Estimates of the lifetime-absorbed daily dose (LADD) of acrylamide resulting from use of representative personal-care products containing polyacrylamides have been developed. All of the parameters that determine the amount of acrylamide absorbed by an individual vary from one individual to another. Moreover, for some parameters there is uncertainty as to which is the correct or representative value from a range of values. Consequently, the parameters used in the estimation of the LADD of acrylamide from usage of a particular product type (e.g., deodorant, makeup, etc.) were represented by distributions evaluated using Monte Carlo analyses.((1-4)) From these data, distributions of values for key parameters, such as the amount of acrylamide in polyacrylamide, absorption fraction, etc., were defined and used to provide a distribution of LADDs for each personal-care product. The estimated total acrylamide LADD (across all products) for males and females at the median, mean, and 95th percentile of the distribution of individual LADD values were 4.7 x 10(-8), 2.3 x 10(-7), and 7.3 x 10(-7) mg/kg/day for females and 3.6 x 10(-8), 1.7 x 10(-7), and 5.4 x 10(-7) mg/kg/day for males. The ratio of the LADDs to risk-specific dose corresponding to a target risk level of 1 x 10(-5), the acceptable risk level for this investigation, derived using approaches typically used by the FDA, the USEPA, and proposed for use by the European Union (EU) were also calculated. All ratios were well below 1, indicating that all the extra lifetime cancer risk from the use of polyacrylamide-containing personal-care products, in the manner assumed in this assessment, are well below acceptable levels. Even if it were assumed that an individual used all of the products together, the estimated LADD would still provide a dose that was well below the acceptable risk levels.

Acrylamide↗
PubMed1971

The separation of alpha-2 macroglobulin into five components with differing electrophoretic and enzyme-binding properties.

The alpha-2 macroglobulins from human serum and plasma were isolated by Bio-Gel P-300 and A5m gel filtration. The material showed a single peak on sedimentation velocity ultracentrifugation, a mol wt of 650,000 by sedimentation equilibrium ultracentrifugation, and a major precipitin arc in the alpha-2 macroglobulin region by immunoelectrophoresis against whole human serum. Two bands were observed in the alpha-2 macroglobulin region when acrylamide gel electrophoresis was performed with a pH 8.9 running gel. When a pH 7.8 gel was used, five electrophoretic species were observed. In both cases, the preaddition of stoichiometric amounts of trypsin or chymotrypsin added to alpha-2 macroglobulin resulted in disappearance of slower bands leaving only one band on acrylamide gel electrophoresis patterns. Preparative acrylamide gel electrophoresis separated alpha-2 macroglobulin obtained from Bio-Gel into five closely-spaced species. Separation was sufficiently adequate to show that those species of alpha-2 macroglobulin which bound trypsin and chymotrypsin were represented by slower moving species and that the fastest moving material had lost virtually all of the ability to bind these enzymes. Preparative acrylamide gel electrophoresis of a mixture of alpha-2 macroglobulin-trypsin complex and alpha-2 macroglobulin revealed that the fast moving component was alpha-2 macroglobulin-trypsin complex and that the slower moving material was unbound alpha-2 macroglobulin. The naturally occurring amidase activity of the alpha-2 macroglobulin using benzoylarginine-p-nitroanilide (BAPNA) as substrate was investigated and unlike its trypsin-binding activity, amidase activity was found to be of the same specific activity in all electrophoretic fractions. Binding of trypsin and chymotrypsin to alpha-2 macroglobulin revealed that alpha-2 macroglobulin maximally bound 2 moles of trypsin and 1 mole of chymotrypsin. When the enzymes were added simultaneously there was competition. Chymotrypsin added to alpha-2 macroglobulin before the addition of trypsin prevented all trypsin binding even though only one site was filled with chymotrypsin. These results were explained by the acrylamide gels which showed that 1 mole of chymotrypsin was sufficient to convert all the alpha-2 macroglobulin to a species with the fastest mobility which no longer binds additional enzyme.

Acrylamides↗
PubMed2006

An extended relationship for the characterization of Young's modulus and Poisson's ratio of tunable polyacrylamide gels.

Substrates with tunable mechanical properties are crucial for the study of cellular processes, and polyacrylamide gels (PAGs) are frequently used in this context. Several experimental techniques have been proposed to obtain the mechanical properties of PAGs. However, the range of the considered Poisson's ratio values remains quite large and no attempt has been made to propose an analytical relationship allowing the estimation of PAG Young's modulus when both bis-acrylamide and acrylamide concentrations are known. In order to complete the actual knowledge on the mechanical properties of PAGs, we took benefit of our original method based on the micropipette aspiration technique (Boudou et al., J. Biomech. 2006) for characterizing gels made with concentrations in the range 0.02% < or =[Bis]< or =0.20% and 3% < or =[Acry]< or =10%. We found that the PAGs Young's modulus varies nonlinearly with the acrylamide amount. Moreover, our study validates the quasi-incompressibility hypothesis usually made in studies using PAGs (mean Poisson's ratio of 0.480+/-0.012). More generally, and in agreement with data published by other groups, we propose an original nonlinear mathematical relationship allowing the computation of Young's modulus of PAG for any given acrylamide and bis-acrylamide amounts taken in the range of values we considered.

Acrylamide↗
PubMed1992

Effect of total percent polyacrylamide in capillary gel electrophoresis for DNA sequencing of short fragments. A phenomenological model.

Polyacrylamide capillary gels were prepared with constant (5% C) cross-linker concentration and with total acrylamide concentration ranging from 2.5 to 6% T. At each acrylamide concentration, peak spacing was constant for DNA sequencing fragments ranging from 25 to 250 nucleotides in length. Peak spacing increased linearly with the total acrylamide concentration. The intercept of the retention time vs. fragment length plot was independent of % T. Ferguson plots were constructed for short DNA fragments; the polyacrylamide pore size falls in the 2.5 to 3.5 nm range for the gels studied. Theoretical plate count is independent of total acrylamide concentration; longitudinal diffusion, and not thermal gradients, limit the plate count. A phenomenological model is presented that predicts retention time, plate count, and resolution for sequencing fragments ranging in size from 25 to 250 bases and gels that range from 2.5 to 6% total acrylamide.

Acrylic Resins↗
PubMed1992

Interaction of dipyridamole with micelles of lysophosphatidylcholine and with bovine serum albumin: fluorescence studies.

The interaction of the coronary vasodilator dipyridamole with biological systems, protein and membranes has been studied through optical absorption and fluorescence spectroscopies. Using the analysis of the spectra and fluorescence intensity of dipyridamole (DIP) in solution, the interaction of this compound with the transport protein albumin (BSA) and with a model of cell membranes, namely micelles of lysophosphatidylcholine (L-PC), was investigated. Measurements were performed at pH 5.0 and pH 7.0 where the molecule of DIP is fully protonated and partially protonated, respectively. The quenching of fluorescence with nitroxide-stable radicals 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) as well as with acrylamide and iodide allowed the localization of the drug in the polar interface of micelles. Quenching by acrylamide and iodide in L-PC micelles demonstrated the effect of micelle protonation which increased the accessibility of iodide to the chromophore. An effective association constant was obtained both at pH 7.0 (7.5 x 10(3) M-1) and pH 5.0 (2.5 x 10(3) M-1) and a very good agreement with the proposed binding model was observed. The quantum yields of fluorescence data agree very well with the fluorescence lifetimes. The measurement of lifetimes was important to understand the kinetic data obtained from Stern-Volmer plots both of radical, acrylamide and iodide quenching of fluorescence. It was observed that, in the presence of micelles, the kq value increased for TEMPO while decreased for TEMPOL. This result, together with the vanishing solubility of DIP in saturated hydrocarbons and the preferential partition of TEMPO in micelles, suggested the localization of DIP in the polar micellar interface. This is also supported by the enhanced iodide quenching at pH 5.0, constancy of acrylamide quenching in the range of pH 7.0-5.0 and the partition of TEMPO and TEMPOL in SDS micelles. The association constant of DIP to BSA was also estimated both at pH 7.0 (2 x 10(4) M-1) and pH 5.0 (4 x 10(3) M-1). Quenching studies with nitroxide radicals, acrylamide and iodide also suggested the binding of the drug to a hydrophobic region of the protein. At pH 5.0, the protein undergo a conformational change which leads to a loosening of the overall structure so that the accessibility of the nitroxide radicals for DIP is increased at this pH. The differences in kq values at pH 7.0 and pH 5.0 suggested that at pH 7.0 the chromophore is protected in the protein site.(ABSTRACT TRUNCATED AT 400 WORDS)

Dipyridamole↗
PubMed2004

Human health risk assessment of processing-related compounds in food.

Many types of food processing techniques have been employed throughout human history, mainly to ensure microbiological and chemical safety of foods and to improve palatability. Growing consumer demand for healthy, nutritious and convenient food is a key driver for improvements and new developments in food processing. New processes or newly recognized compounds, often identified due to improved analytical capabilities, require careful evaluation of potential human health impact. As examples for processing-related contaminants, the risk assessments for 3-monochloropropanediol (3-MCPD) and acrylamide are discussed, exemplifying two traditional approaches in food safety assessment. 3-MCPD is formed in a variety of industrially and domestically produced foods in the presence of fat and chloride. 3-MCPD is considered a non-genotoxic carcinogen, hence a threshold of effect is assumed and sufficient data are available to establish a safe level of intake. The recent discovery of the formation of acrylamide in certain high heat-treated foods, domestically or industrially, has raised considerable concern, since acrylamide, besides neurotoxicity and reproductive toxicity, is considered as genotoxic carcinogen. Unavoidable substances considered to be genotoxic carcinogens are unwanted in foods and are usually dealt with via the ALARA principle. However, for such unavoidable substances, a quantitative risk assessment may give more useful advice to risk managers for appropriate actions. Currently, adequate dose-response relationships and mechanistic information regarding carcinogenicity of acrylamide are lacking. Once this information becomes available, the health risk from acrylamide exposure through food can be assessed.

Animals↗
PubMed2006

Mechanistic evidence for intermolecular radical carbonyl additions promoted by samarium diiodide.

In this work, mechanistic studies were performed to understand the SmI2/H2O-mediated coupling of N-acyl oxazolidinones with acrylates and acrylamides, providing gamma-keto esters and amides, respectively. Our results provide experimental evidence that C-C bond formation via intermolecular radical addition reactions to carbonyl substrates can be promoted by samarium diiodide. Coupling reactions with N-cyclopropylcarbonyl-2-oxazolidinone suggest the alpha,beta-unsaturated esters/amides are reduced by the low-valent lanthanide reagent and not the N-acyl oxazolidinones, as originially proposed (J. Am. Chem. Soc. 2005, 127, 6544). Rate measurements support the preferred reduction of an acrylate or acrylamide by SmI2/H2O in the presence of an N-acyl oxazolidinone. In the absence of the N-acyl oxazolidinone, SmI2/H2O promotes dimerization of the acrylates, whereas the C=C bond of the acrylamides is reduced. In addition, coupling of the Pfp ester of Cbz-protected phenylalanine with an acrylamide leads only to reduction of the acrylamide and recovered ester, whereas the same coupling with the N-acyl oxazolidinone derivative provides the gamma-keto amides. These results imply that a pathway involving nucleophilic acyl substitution cannot take place and that a radical mechanism must be invoked to explain the C-C bond formation. We propose that the acrylate/acrylamide is reduced to a conjugated ketyl radical that adds to the exocyclic carbonyl group of the N-acyl oxazolidinone, activated through bidentate coordination to a lanthanide ion.

Journal Article↗