Incorporation of phenylcarbonyl groups in the sidechain: A tool to induce ordered assembly of peptides on surfaces.

The possibility of introducing various functionalities on peptides with relative ease allows them to be used for molecular applications. However, oligopeptides prepared entirely from proteinogenic amino acids seldom assemble as ordered structures on surfaces. Therefore, sidechain modifications of peptides that can increase the intermolecular interactions without altering the constitution of a given peptide become an attractive route to self-assembling them on surfaces.

Enhancing Photocatalytic Attributes of Perovskite Nanocrystals in Aqueous Media via Ligand Engineering.

The remarkable catalytic potential of perovskite nanocrystals (NCs) remains underutilized due to their limited stability in polar media, resulting from the vulnerability of their structure to disruption by polar solvents. In this study, we address this challenge by employing the bolaamphiphilic NKE-12 ligand, which features multiple denticities to effectively shield the surface of CsPbBr NCs from polar solvent interactions without compromising their light-harvesting properties. Our research, utilizing electrochemical impedance and photocurrent response measurements, highlights efficient charge separation and charge transfer enabled by NKE-12 ligands, which feature multiple ionic groups and peptide bonds, compared to conventional oleylamine/oleic acid ligands on CsPbBr NCs.

Amphiphilic conjugates of ferrocene with amino acids and peptides: Design, synthesis, and studies on their aggregation behavior.

A new class of ferrocenyl surfactants based on covalent linkage between amino acids or peptides and ferrocene was designed. Accordingly, five ferrocenyl amphiphiles, FcS1-5, were synthesized, and their aggregation behaviors in aqueous solutions were studied. Compared to the other surfactants containing ferrocenyl units, FcS have a relatively smaller size and low molecular weight and are easy to synthesize.

Revealing the Limits of Intermolecular Interactions: Molecular Rings of Ferrocene Derivatives on Graphite Surface.

We report the formation of discrete molecular rings/spirals of small molecules (1,3-dithia derivatives of ferrocene) on a highly oriented pyrolytic graphite (HOPG) surface. On the basis of microscopy and theoretical calculations, molecular level arrangement within the molecular rings is understood. The molecular rings show a limiting inner diameter, and we interpret it to be related to the critical intermolecular interaction limit.

Synthesis of peptides containing oxo amino acids and their crystallographic analysis.

An isolated uncharged hydrogen bond acceptor such as the carbonyl functionality of an aldehyde or a keto group is absent in natural amino acids. Although glutamine and asparagine are known to hydrogen bond through the amide carbonyl group in their side chains, they also possess the amide NH group, which can act as a hydrogen bond donor. This makes the structural study of peptides containing an oxo residue, with an isolated carbonyl group in the side chain, interesting.

d-Prolyl-2-(trifluoromethylsulfonamidopropyl)pyrrolidine: An Organocatalyst for Asymmetric Michael Addition of Aldehydes to β-Nitroalkenes at Ambient Conditions.

Four 2-(trifluoromethylsulfonamidoalkyl)pyrrolidines and their d-prolinamides were prepared and screened as organocatalysts for the Michael addition reaction of aldehydes with β-nitroalkenes at rt and without the use of additives. d-Prolyl-2-(trifluoromethylsulfonamidopropyl)pyrrolidine was found to be the best among the molecules studied, which yielded γ-nitro aldehydes in very high yields (up to 95%), with high diastereoselectivity (up to >99:1) and with up to 97% ee.

Enantioselective Synthesis of 2-Aminomethyl and 3-Amino Pyrrolidines and Piperidines through 1,2-Diamination of Aldehydes.

An efficient method for the synthesis of 1,2-diamines from aldehydes through proline-catalyzed asymmetric α-amination followed by reductive amination is reported. The products resemble those obtained through direct asymmetric diamination of terminal alkenes. The methodology is used to synthesize 2-aminomethyl and 3-amino pyrrolidines and piperidines in high yields and with a good enantioselectivity.

A bromo-capped diruthenium(i,i) N-heterocyclic carbene compound for in situ bromine generation with NBS: catalytic olefin aziridination reactions.

A bromo-capped metal-metal bonded diruthenium(i,i) complex Ru2(CO)4(PIN)2Br2 (1) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene) generates bromine with N-bromosuccinimide (NBS) at room temperature. Cycloalkene and stilbene are readily brominated by stoichiometric reactions with 1 and NBS. An analysis of the dibrominated products suggests the formation of cyclic bromonium intermediates indicating in situ Br2 generation.

Diastereoselective synthesis of furanose and pyranose substituted glycine and alanine derivatives via proline-catalyzed asymmetric α-amination of aldehydes.

A concise organocatalytic route toward the synthesis of furanose and pyranose substituted glycine and alanine derivatives is reported. These compounds are core structural units of some of the naturally available antibiotics and antifungal agents. Proline-catalyzed asymmetric α-amination of aldehydes derived from sugars is used as the key reaction to synthesize twelve sugar amino acid derivatives.

Click Chemistry Route to the Synthesis of Unusual Amino Acids, Peptides, Triazole-Fused Heterocycles and Pseudodisaccharides.

Conjugation of different molecular species using copper(I)-catalyzed click reaction between azides and terminal alkynes is among the best available methods to prepare multifunctional compounds. The effectiveness of this method has provided wider acceptance to the concept of click chemistry, which is now widely employed to synthesize densely functionalized organic molecules. This article summarizes the contributions from our group in the development of new methods for the synthesis of functional molecules using copper(I)-catalyzed click reactions.

Synthesis of stable C-linked ferrocenyl amino acids and their use in solution-phase peptide synthesis.

Incorporation of ferrocenyl group to peptides is an efficient method to alter their hydrophobicity. Ferrocenyl group can also act as an electrochemical probe when incorporated onto functional peptides. Most often, ferrocene is incorporated onto peptides post-synthesis via amide, ester or triazole linkages.

Divergent synthesis of various iminocyclitols from D-ribose.

A very efficient route to the diastereoselective synthesis of polyhydroxy pyrrolidines, piperidines and azepanes from an aldehyde derivative of ribose is reported. Asymmetric α-amination of aldehydes using proline catalysed hydrazination is the key step in the synthesis. The method utilizes the stereocenters present in ribose and the extra carbon atoms present in the target molecules are incorporated using Wittig reactions.

Diastereoselective Synthesis of 1-Deoxygalactonojirimycin, 1-Deoxyaltronojirimycin, and N-Boc-(2S,3S)-3-Hydroxypipecolic Acid via Proline Catalyzed α-Aminoxylation of Aldehydes.

An efficient synthesis of deoxygalactonojirimycin and deoxyaltronojirimycin through the use of proline catalyzed asymmetric α-aminoxylation of a higher homologue of Garner's aldehyde, derived from l-aspartic acid, is reported. The method is also used for a highly diastereoselective synthesis of the N-Boc derivative of (2S,3S)-3-hydroxypipecolic acid. The configuration of the proline catalyst used for the asymmetric aminoxylation step ultimately controls the absolute configuration of three adjacent stereogenic centers in the final products.

A highly efficient catalyst for selective oxidative scission of olefins to aldehydes: abnormal-NHC-Ru(II) complex in oxidation chemistry.

The utility and selectivity of the catalyst [Ru(COD)(L(1))Br2] (1) bearing a fused π-conjugated imidazo[1,2-a][1,8]naphthyridine-based abnormal N-heterocyclic carbene ligand L(1) is demonstrated toward selective oxidation of C═C bonds to aldehydes and C≡C bonds to α-diketones in an EtOAc/CH3CN/H2O solvent mixture at room temperature using a wide range of substrates, including highly functionalized sugar- and amino acid-derived compounds.

Powerful binders for the D-dimer by conjugation of the GPRP peptide to polypeptides from a designed set--illustrating a general route to new binders for proteins.

The synthetic tetrapeptide GPRP based on the amino-terminal GPR sequence of the fibrin α-chain binds the D-dimer protein with a dissociation constant K(D) of 25 μM. The D-dimer protein, a well-known biomarker for thrombosis, contains two cross-linked D fragments from the fibrinogen protein formed upon degradation of the fibrin gel, the core component of blood clots. In order to develop a specific high-affinity binder for the D-dimer protein, GPRP was conjugated via an aliphatic spacer to each member of a set of sixteen polypeptides designed for the development of binder molecules for proteins in general.

Applications of propargyl esters of amino acids in solution-phase Peptide synthesis.

Propargyl esters are employed as effective protecting groups for the carboxyl group during solution-phase peptide synthesis. The propargyl ester groups can be introduced onto free amino acids by treating them with propargyl alcohol saturated with HCl. The reaction between propargyl groups and tetrathiomolybdate is exploited to deblock the propargyl esters.

An improved procedure for the synthesis of dehydroamino acids and dehydropeptides from the carbonate derivatives of serine and threonine using tetrabutylammonium fluoride.

Dehydroamino acids are important precursors for the synthesis of a number of unnatural amino acids and are structural components in many biologically active peptide derivatives. However, efficient synthetic procedures for their production in large amounts and without side reactions are limited. We report here an improved procedure for the synthesis of dehydroalanine and dehydroamino butyric acid from the carbonate derivatives of serine and threonine using TBAF.

Development and characterization of lysine based tripeptide analogues as inhibitors of Sir2 activity.

Sirtuins are NAD(+) dependent deacetylases that modulate various essential cellular functions. Development of peptide based inhibitors of Sir2s would prove useful both as pharmaceutical agents and as effectors by which downstream cellular alterations can be monitored. Click chemistry that utilizes Huisgen's 1,3-dipolar cycloaddition permits attachment of novel modifications onto the side chain of lysine.

One-pot protection and activation of amino acids using pentafluorophenyl carbonates.

Protection of the amino group and activation of the carboxylic acid groups are the most important steps associated with any peptide synthesis protocol; hence, a one-pot process to achieve these is highly desirable. A possible strategy is to use pentafluorophenyl carbonates to simultaneously protect the amino group as a carbamate derivative and activate the carboxylic acid group as a pentafluorophenyl ester. A detailed study is carried out to understand the scope and limitations of this method using five different pentaflurophenyl carbonates.

Simultaneous protection and activation of amino acids using propargyl pentafluorophenyl carbonate.

[reaction: see text] A very efficient method for the simultaneous protection of the amino group and activation of the carboxyl group of amino acids is reported using propargyl pentafluorophenyl carbonate (PocOPfp). The amino group is protected as a propargyloxycarbonyl (Poc) derivative, and the carboxyl group is activated as a pentafluorophenyl ester. The yields obtained are good to excellent ranging from 60 to 87%.