SciCombinator

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Concept: Amide

169

We report on how to quantify the binding affinity between a nanoparticle and chemical functional group using various experimental methods such as cantilever assay, PeakForce quantitative nanomechanical property mapping, and lateral force microscopy. For the immobilization of Au nanoparticles (AuNPs) onto a microscale silicon substrate, we have considered two different chemical functional molecules of amine and catecholamine (dopamine was used here). It is revealed that catecholamine-modified surface is more effective for the functionalization of AuNPs onto the surface, which is compared with the amine-modified surface from our various experiments. The dimensionless parameter (i.e., ratio of binding affinity) introduced in this work from such experiments is useful in quantitatively depicting such binding affinity, indicating that the binding affinity and stability between AuNPs and catecholamine is approximately 1.5 times stronger than that of amine. Our study sheds light on the experiment-based quantitative characterization of the binding affinity between nanomaterial and chemical groups, which will eventually provide an insight into how to effectively design the functional material using chemical groups.

Concepts: Amine, Nanoparticle, Functional group, Nanotechnology, Gold, Alkene, Amide, Imine

31

One of the most important reactions in organic chemistry–amide bond formation–is often overlooked as a contemporary challenge because of the widespread occurrence of amides in modern pharmaceuticals and biologically active compounds. But existing methods are reaching their inherent limits, and concerns about their waste and expense are becoming sharper. Novel chemical approaches to amide formation are therefore being developed. Here we review and summarize a new generation of amide-forming reactions that may contribute to solving these problems. We also consider their potential application to current synthetic challenges, including the development of catalytic amide formation, the synthesis of therapeutic peptides and the preparation of modified peptides and proteins.

Concepts: Protein, Oxygen, Amino acid, Chemical reaction, Peptide bond, Nitrogen, Amide, Peptide synthesis

28

We previously reported the apparent formation of matrix adducts of 3,5-dimethoxy-4-hydroxy-cinnamic acid (sinapinic acid or SA) via covalent attachment to disulfide bond-containing proteins (HdeA, Hde, and YbgS) from bacterial cell lysates ionized by matrix-assisted laser desorption/ionization (MALDI) time-of-flight-time-of-flight tandem mass spectrometry (TOF-TOF-MS/MS) and post-source decay (PSD). We also reported the absence of adduct formation when using α-cyano-4-hydroxycinnamic acid (CHCA) matrix. Further mass spectrometric analysis of disulfide-intact and disulfide-reduced over-expressed HdeA and HdeB proteins from lysates of gene-inserted E. coli plasmids suggests covalent attachment of SA occurs not at cysteine residues but at lysine residues. In this revised hypothesis, the attachment of SA is preceded by formation of a solid phase ammonium carboxylate salt between SA and accessible lysine residues of the protein during sample preparation under acidic conditions. Laser irradiation at 355 nm of the dried sample spot results in equilibrium retrogradation followed by nucleophilic attack by the amine group of lysine at the carbonyl group of SA and subsequent amide bond formation and loss of water. The absence of CHCA adducts suggests that the electron-withdrawing effect of the α-cyano group of this matrix may inhibit salt formation and/or amide bond formation. This revised hypothesis is supported by dissociative loss of SA (-224 Da) and the amide-bound SA (-206 Da) from SA-adducted HdeA and HdeB ions by MS/MS (PSD). It is proposed that cleavage of the amide-bound SA from the lysine side-chain occurs via rearrangement involving a pentacyclic transition state followed by hydrogen abstraction/migration and loss of 3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-ynal (-206 Da).

Concepts: Protein, Oxygen, Amino acid, Acid, Ammonia, Mass spectrometry, Nitrogen, Amide

28

We report here a two step efficient route for the synthesis of 1,2,3,4-tetrahydro-β-carboline (THBC)-based tetracyclic peptidomimetics from a Ugi 4-CR/Pictet-Spengler reaction sequence. Suitably N-protected 2-aminoacetaldehyde was for the first time applied as the carbonyl component in a Ugi four-component reaction, opening the way to the employment of N-protected α-amino acid-derived aldehydes in the same role. The potential of the obtained scaffolds is related to the possibility of further derivatization with the desired pharmacophoric groups, on both the terminal acid and amine functional groups, for the development of conformationally constrained tryptophan-containing peptide ligands. Extensive molecular modeling and (1)H NMR studies highlighted a robust, folded, β-turn-like conformation for one of these peptidomimetic compounds.

Concepts: Alcohol, Amine, Functional group, Alkene, Carbonyl, Carboxylic acid, Amide, Imine

28

We developed a new conjugated cruciform flourophore (XF) featuring imine groups. The condensation of an XF containing aldehyde functionalities and selected primary amines leads to several XF- imine derivatives. Upon addition of Cu2+ or Zn2+ ions to solutions of the imine XFs in different solvents a red shifted emission is detected, resulting in an altering emission color. The imine here acts as a metallo-reactive fluorophor.

Concepts: Amino acid, Amine, Functional group, Alkene, Carbonyl, Amide, Imine, Alkylimino-de-oxo-bisubstitution

28

The dynamic kinetic resolution of α-keto esters via asymmetric transfer hydrogenation has been developed as a technique for the highly stereoselective construction of structurally diverse β-substituted-α-hydroxy carboxylic acid derivatives. Through the development of a privileged m-terphenylsulfonamide for (arene)RuCl(monosulfonamide) complexes with a high affinity for selective α-keto ester reduction, excellent levels of chemo-, diastereo-, and enantiocontrol can be realized in the reduction of β-aryl- and β-chloro-α-keto esters.

Concepts: Alcohol, Amino acid, Stereochemistry, Hydrogenation, Acetic acid, Carboxylic acid, Ester, Amide

28

Upon treatment with phenyl dichlorophosphate (PhOP=OCl(2)) in acetonitrile at ambient temperature, a variety of ketoximes underwent a Beckmann rearrangement in an effective manner to afford the corresponding amides in moderate to high yields.

Concepts: Amide, Beckmann rearrangement, Ernst Otto Beckmann, Rearrangement reaction

28

The synthesis of 4',6'-dihydrospiro[piperidine-4,5'-pyrazolo[3,4-c]pyridin]-7'(2'H)-one-based acetyl-CoA carboxylase inhibitors is reported. The hitherto unknown N-2 tert-butyl pyrazolospirolactam core was synthesized from ethyl 3-amino-1H-pyrazole-4-carboxylate in a streamlined 10-step synthesis requiring only one chromatography procedure. The described synthetic strategy provides pyrazolo-fused spirolactams from halogenated benzylic arenes and cyclic carboxylates. Key steps include a regioselective pyrazole alkylation providing the N-2 tert-butyl pyrazole and a Curtius rearrangement under both conventional and flow conditions to install the hindered amine via a stable and isolable isocyanate. Finally, a Parham-type cyclization was used to furnish the desired spirolactam. An analogous route provided efficient access to the related N-1 isopropyl lactam series. Elaboration of the lactam cores via amidation enabled synthesis of novel ACC inhibitors and the identification of potent analogues.

Concepts: Amine, Functional groups, Carboxylic acid, Amide, Alkyl, Beckmann rearrangement, Schmidt reaction, Organic reactions

27

N-Formylsaccharin, an easily accessible crystalline compound, has been employed as an efficient CO source in Pd-catalyzed fluorocarbonylation of aryl halides to afford the corresponding acyl fluorides in high yields. The reactions use a near-stoichiometric amount of the CO source (1.2 equiv) and tolerate diverse functional groups. The acyl fluorides obtained could be readily transformed into various carboxylic acid derivatives such as carboxylic acid, esters, thioesters, and amides in a one-pot procedure.

Concepts: Alcohol, Amine, Functional group, Carbonyl, Acetic acid, Functional groups, Carboxylic acid, Amide

27

A copper-catalyzed coupling of α-oxocarboxylic acids with formamides is reported. This simple method provides a practical approach toward the synthesis of α-ketoamides with a variety of functional groups. Mechanistic studies have shown that the reaction proceeded via a radical process and (13)C-labeled experiments proved that the amide carbon in the products comes from the corresponding carboxylic acid, not from the DMF.

Concepts: Alcohol, Amino acid, Amine, Functional group, Carbonyl, Acetic acid, Carboxylic acid, Amide