- Engineering a polymeric chiral catalyst by using hydrogen bonding and coordination interactions
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(Chemical Equation Presented) Noncovalent interactions are used to generate a polymeric supramolecular chiral catalyst (see picture). This heterogeneous catalyst, which is based on Feringa's MonoPhos/RhI system, is formed by orthogonal self-ass
- Shi, Lei,Wang, Xingwang,Sandoval, Christian A.,Li, Mingxing,Qi, Qiaoyan,Li, Zhanting,Ding, Kuiling
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Read Online
- Oxidative Damage in Aliphatic Amino Acids and Di- and Tripeptides by the Environmental Free Radical Oxidant NO3?: the Role of the Amide Bond Revealed by Kinetic and Computational Studies
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Kinetic and computational data reveal a complex behavior of the important environmental free radical oxidant NO3? in its reactions with aliphatic amino acids and di- and tripeptides, suggesting that attack at the amide N-H bond in the peptide backbone is a highly viable pathway, which proceeds through a proton-coupled electron transfer (PCET) mechanism with a rate coefficient of about 1 × 106 M-1 s-1 in acetonitrile. Similar rate coefficients were determined for hydrogen abstraction from the α-carbon and from tertiary C-H bonds in the side chain. The obtained rate coefficients for the reaction of NO3? with aliphatic di- and tripeptides suggest that attack occurs at all of these sites in each individual amino acid residue, which makes aliphatic peptide sequences highly vulnerable to NO3?-induced oxidative damage. No evidence for amide neighboring group effects, which have previously been found to facilitate radical-induced side-chain damage in phenylalanine, was found for the reaction of NO3? with side chains in aliphatic peptides.
- Nathanael, Joses G.,Wille, Uta
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p. 3405 - 3418
(2019/03/11)
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- Oxidative functionalization of aliphatic and aromatic amino acid derivatives with H2O2 catalyzed by a nonheme imine based iron complex
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The oxidation of a series of N-acetyl amino acid methyl esters with H2O2 catalyzed by a very simple iminopyridine iron(ii) complex 1 easily obtainable in situ by self-assembly of 2-picolylaldehyde, 2-picolylamine, and Fe(OTf)2 was investigated. Oxidation of protected aliphatic amino acids occurs at the α-C-H bond exclusively (N-AcAlaOMe) or in competition with the side-chain functionalization (N-AcValOMe and N-AcLeuOMe). N-AcProOMe is smoothly and cleanly oxidized with high regioselectivity affording exclusively C-5 oxidation products. Remarkably, complex 1 is also able to catalyze the oxidation of the aromatic N-AcPheOMe. A marked preference for the aromatic ring hydroxylation over Cα-H and benzylic C-H oxidation was observed, leading to the clean formation of tyrosine and its phenolic isomers.
- Ticconi, Barbara,Colcerasa, Arianna,Di Stefano, Stefano,Lanzalunga, Osvaldo,Lapi, Andrea,Mazzonna, Marco,Olivo, Giorgio
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p. 19144 - 19151
(2018/05/31)
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- Simple and efficient Fmoc removal in ionic liquid
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A mild method for an efficient removal of the fluorenylmethoxycarbonyl (Fmoc) group in ionic liquid was developed. The combination of a weak base such as triethylamine and [Bmim][BF4] makes the entire system more efficient for the cleavage at room temperature of various amines and amino acid methyl esters in short reaction times. The procedure works well even in the case of N-Fmoc amino acids bearing acid-sensitive protecting groups and of N-alkylated amino acid methyl esters. The solvent-free condition provides a complementary method for Fmoc deprotection in solution phase peptide synthesis and modern organic synthesis.
- Di Gioia,Costanzo,De Nino,Maiuolo,Nardi,Olivito,Procopio
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p. 36482 - 36491
(2017/08/02)
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- IMMUNOSTIMULATING AGENT
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The present invention aims to provide an immunostimulating agent superior in an immunostimulatory effect, particularly a compound useful as a vaccine adjuvant, a pharmaceutical composition containing the compound, a vaccine containing the compound and an
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Paragraph 0181
(2017/05/21)
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- Deprotection/reprotection of the amino group in α-amino acids and peptides. A one-pot procedure in [Bmim][BF4] ionic liquid
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This paper presents an efficient one-pot protocol for the sequential deprotection/reprotection of the α-amino group in α-amino acid and dipeptide methyl esters. [Bmim][BF4] is used as the solvent in the entire process. In particular, the use of the ionic liquid allows for rapid and clean removal of the 4-nitrobenzenesulfonyl (nosyl) group and for facile subsequent tert-butyloxycarbonylation of the free α-amino function under very mild conditions. N-Boc-α-amino acid as well as peptide derivatives are isolated in excellent yields, and do not require any further purification. Absolute configurations of the precursors are totally preserved during the process.
- Di Gioia,Barattucci,Bonaccorsi,Leggio,Minuti,Romio,Temperini,Siciliano
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p. 2678 - 2686
(2014/01/06)
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- A new method for peptide synthesis in the N→C direction: Amide assembly through silver-promoted reaction of thioamides
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The Ag(i)-promoted coupling of amino acids and peptides with amino ester thioamides generates peptide imides without epimerisation. The peptide imides undergo regioselective hydrolysis under mild conditions to generate native peptides. This method was employed to prepare the pentapeptide thymopentin in the N→C direction, in high yield and purity.
- Pourvali, Aysa,Cochrane, James R.,Hutton, Craig A.
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supporting information
p. 15963 - 15966
(2015/01/09)
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- Deprotectlon of N-Nosyl-α-amlno acids by using solid-supported mercaptoacetic acid
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A simple and efficient synthesis of a solid-supported thiol has been developed. Mercaptoacetic acid was first protected by the dimethoxytrityl group and then anchored to Wang resin through an ester bond. Deprotection of the thiol function led to resin-supported mercaptoacetic acid, a useful supported thiol reagent that can be used in the polymer-assisted solution-phase removal of nosyl (Ns) groups from the amino function of a-amino acids in peptide synthesis.
- De Marco, Rosaria,Gioia, Maria Luisa Di,Leggio, Antonella,Liguori, Angelo,Viscomi, Maria Caterina
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experimental part
p. 3795 - 3800
(2009/12/05)
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- Oxidation of peptides by methyl(trifluoromethyl)dioxirane: The protecting group matters
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Representative Boc-protected and acetyl-protected peptide methyl esters bearing alkyl side chains undergo effective oxidation using methyl(trifluoromethyl)dioxirane (1b) under mild conditions. We observe a protecting group dependency in the chemoselectivity displayed by the dioxirane 1b. N-Hydroxylation occurs in the case of the Boc-protected peptides, and side chain hydroxylation takes place in the case of acetyl-protected peptides. Both are attractive transformations since they yield derivatized peptides that serve as valuable synthons.
- Rella, Maria Rosaria,Williard, Paul G.
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p. 525 - 531
(2007/10/03)
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- Application of chiral mixed phosphorus/sulfur ligands to enantioselective rhodium-catalyzed dehydroamino acid hydrogenation and ketone hydrosilylation processes
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Chiral mixed phosphorus/sulfur ligands 1-3 have been shown to be effective in enantioselective Rh-catalyzed dehydroamino acid hydrogenation and ketone hydrosilylation reactions (eqs 1, 2). After assaying the influence of the substituents at sulfur, the substituents on the ligand backbone, the relative stereochemistry within the ligand backbone, and the substituents at phosphorus, ligands 2c (R = 3,5-dimethylphenyl) and 3 were found to be optimal in the Rh-catalyzed hydrogenation of a variety of α-acylaminoacrylates in high enantioselectivity (89-97% ee). A similar optimization of the catalyst for the Rh-catalyzed hydrosilylation of ketones showed that ligand 3 afforded the highest enantioselectivities for a wide variety of aryl alkyl and dialkyl ketones (up to 99% ee). A model for asymmetric induction in the hydrogenation reaction is discussed in the context of existing models, based on the absolute stereochemistry of the products and the X-ray crystal structures of catalyst precursors and intermediates.
- Evans, David A.,Michael, Forrest E.,Tedrow, Jason S.,Campos, Kevin R.
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p. 3534 - 3543
(2007/10/03)
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- "One-pot" methylation of N-nosyl-α-amino acid methyl esters with diazomethane and their coupling to prepare N-methyl dipeptides
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N-Nosyl-α-amino acid methyl esters are methylated quantitatively with diazomethane. After proper deprotection of the amino function by treatment with the reagent system mercaptoacetic acid/sodium methoxide, the obtained N-methyl amino acid methyl esters are coupled with N-Fmoe amino acid chlorides to afford the corresponding dipeptides. The obtained products do not show any detectable extent of racemization by 1H NMR and HPLC.
- Di Gioia, Maria Luisa,Leggio, Antonella,Le Pera, Adolfo,Liguori, Angelo,Napoli, Anna,Siciliano, Carlo,Sindona, Giovanni
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p. 7416 - 7421
(2007/10/03)
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- Catalytic asymmetric hydrogenation of α-(acetamido)acrylates using TRAP trans-chelating chiral bisphosphine ligands: Remarkable effects of ligand P-substituent and hydrogen pressure on enantioselectivity
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The catalytic asymmetric hydrogenation of α-(acetamido)acrylates was carded out with the rhodium complexes prepared from [Rh(cod)2]BF4 and trans-chelating chiral bisphosphine ligands, (S,S)-2,2'-bis[(R)-1-(dialkylphosphino)ethyl]-1,1
- Kuwano,Sawamura,Ito
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p. 2571 - 2578
(2007/10/03)
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- Carbohydrate Phosphinites as Practical Ligands in Asymmetric Catalysis: Electronic Effects and Dependence of Backbone Chirality in Rh-Catalyzed Asymmetric Hydrogenations. Synthesis of R- or S-Amino Acids Using Natural Sugars as Ligand Precursors
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Vicinal diarylphosphinites derived from carbohydrates are excellent ligands for the Rh(I)-catalyzed enantioselective asymmetric hydrogenation of dehydroamino acid derivatives, producing the highest enantioselectivity of any ligands directly prepared from natural products. The enantioselectivity can be enhanced by the appropriate choice of substituents on the aromatic rings of the phosphinites. For example, the use of phosphinites with electron-donating bis(3,5-dimethylphenyl) groups on phosphorus provides ee's up to 99% for a wide range of amino acids including some with easily removable N-protecting groups. Electron-withdrawing aryl substituents, on the other hand, decrease the enantioselectivity. Sense of chiral induction in the amino acid product depends on the relative juxtaposition of the vicinal diphosphinites on a given sugar backbone. When readily available D-glucopyranosides are used as the starting sugars, 2,3-phosphinites give the S-amino acids and 3,4-phosphinites give the R-amino acids. In the case of aromatic and heteroaromatic amino acids, enantioselectivities > 95% are consistently obtained. Practical considerations such as the ease of ligand synthesis, rates of reactions, catalyst turnover, and scope and limitations in terms of substrates are discussed. A possible explanation for the enhancement of enantioselectivity by electron-rich phosphinites is offered.
- RajanBabu,Ayers, Timothy A.,Halliday, Gary A.,You, Kimberly K.,Calabrese, Joseph C.
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p. 6012 - 6025
(2007/10/03)
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- Selectivity in Carbonic Anhydrase Catalyzed Hydrolysis of Standard N-Acetyl-DL-amino Acid Methyl Esters
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Carbonic anhydrase-catalyzed hydrolysis of some standard N-acetyl-DL-amino acid methyl esters proceeds with high enantioselectivity.This enzyme hydrolyses selectively D amino acid derivatives in contrast to proteases which have a L stereoselectivity. Key Words: carbonic anhydrase, hydrolysis, N-acetyl-DL-amino acid methyl esters, enantioselectivity.
- Chenevert, Robert,Rhlid, Rachid Bel,Letourneau, Martin,Gagnon, Rene,D'Astous, Linda
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p. 1137 - 1140
(2007/10/02)
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- Catalysis by β-cyclodextrin in the reaction of p-nitrophenyl acetate with α-amino acids
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The reactions of p-nitrophenyl acetate, 1, with both enantiomers of the following α-amino acids: alanine (2a), methionine (2b), leucine (2c), and tryptophan (2d), were studied in the presence of β-cyclodextrin (β-CD).All the reactions were catalyzed by β-
- Barra, Monica,Rossi, Rita H. de
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p. 1124 - 1130
(2007/10/02)
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- NITROSATION OF PEPTIDE BONDS. CLEAVAGE OF NITROSATED PEPTIDES BY PYRROLIDINE AND α-AMINO ESTERS
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The reaction of several α-amino acids and peptides (containing Gly, L-Ala, L-Leu, L- or DL-Phe, and/or L- or D-Val) with air-diluted nitrogen oxides has been studied to roughly mimic the N-nitrosation of peptide bonds that the contaminated urban air might produce in pulmonary tissues. Most N-protected α-amino acids give practically quantitative yields of N-nitroso derivatives. N-Protected dipeptides afford either dinitrosated peptides, mixtures of di- and mononitrosated compounds, selectively mononitrosated products, or no reaction at all, depending mainly on steric effects. The same trends are observed for some higher peptides.The (poly)nitrosated peptides, which retain the chirality of the starting materials, have been characterized by 1H and 13C NMR spectroscopy and are cleaved by pyrrolidine and amino esters under mild conditions to give (new) amides or peptides plus diazo derivatives.
- Garcia, Jordi,Gonzalez, Javier,Segura, Ramon,Vilarrasa, Jaume
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p. 3121 - 3128
(2007/10/02)
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- Process for resolving D, L-leucine
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Production of optically pure D-leucine and L-leucine ester by treating a racemic mixture of N-acyl-D,L-leucine ester with a proteolytic enzyme and separating the resulting N-acyl-L-leucine and N-acyl-D-leucine ester from the solution with subsequent removal of the N-acyl and ester groups to provide L-leucine and D-leucine, respectively.
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- Catalytic Asymmetric Hydrogenation of Methyl (E)- and (Z)-2-Acetamido-3-alkylacrylates
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Rhodium-chiral phosphine complex catalyzed homogeneous hydrogenations of methyl (Z)- and (E)-2-acetamido-4-methoxybut-2-enoates ((Z,E)-10), methyl (Z)- and (E)-2-acetamidohex-2-enoates ((Z,E)-16A) and methyl (Z)- and (E)-2-acetamido-4-methylpent-2-enoates ((Z,E)-16B) are reported.With phosphines in which two achiral phosphorus atoms are connected by a chiral four-carbon unit, higher product enantiomeric excesses (ee's) are obtained from E than from Z substrates.With phosphines in which a two-carbon chiral unit separates two achiral phosphorus atoms, Z substrates are preferred.With dipamp (28), both Z and E substrates (particularly (Z,E)-16A) are reduced with high enantioselectivity.The additional oxygen atom in substrates (Z,E)-10 has little effect on product ee with most phosphines.
- Scott, John W.,Keith, Dennis D.,Nix, George,Parrish, David R.,Remington, Stuart,et al.
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p. 5086 - 5093
(2007/10/02)
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