"Fluorine Effects" in Conformational Orchestration of α/β Hybrid Peptide with a 9-membered Pseudo β-Turn Motif

Fluorine, the tiny robust atom, with its unique features has captured the attention of scientists in recent times, especially in drug discovery with its integration in small molecules, peptides, and proteins. However, studies to understand the 'fluorine effects' on the conformation of molecules that follow 'beyond the rule of 5' are in the infancy yet significant in molecular design and function. For the first time, using short hybrid peptide sequence as an appropriate model, we examined the substitution effect (size, stereoelectronic effect, and hydrogen bonding) using X-ray diffraction, 2D-NMR, and CD studies. The comparative study on their folding patterns with hydrogen-substituted analogs can provide valuable insights into fluorinated substrates' design.

Direct access to carbamates via acylation of arylamines with dialkyl azodicarboxylates under metal-free conditions

A novel C-N coupling of various arylamines with dialkyl azodicarboxylates under metal-free conditions for the rapid assembly of carbamates has been achieved. This established protocol features mild reaction conditions, simple operation, broad substrate scope, moderate to excellent yields and good tolerance of functional groups. Moreover, the potential synthetic utility of products was exemplified by a series of intriguing chemical operations.

Enantiopure β3-Trifluoromethyl-β3-homoalanine Derivatives: Coupling with Boc-Protected Amino Acids and Conformational Studies of Peptides in Solid State

The use of enantiopure β3-trifluoromethyl-β3-alkyl β-amino acids for the design of peptides would contribute to drastically enhance peptide stability in vivo. Moreover, the steric hindrance generated by the substituents on the tetrasubstituted carbon adjacent to the nitrogen function coupled to the electron-withdrawing effect of the trifluoromethyl group is more likely to influence the 3D conformation of the peptide. Herein, we describe a short, scalable and robust method to synthesize N- and/or C-protected enantiopure (R)- and (S)-β3-trifluoromethyl-β3-methyl β-amino acid derivatives and liquid-phase coupling methods suitable for incorporation of Boc-protected amino acids into short α/β- and β-peptides. Conformational studies of some of these original peptides via X-ray diffraction analysis highlighted intraresidue C6 hydrogen bonds within trifluoromethylated amino acids.

Crystal structure and Hirshfeld surface analysis of di-chlorido-(methanol-κO)bis-(2-methyl-pyridine-κN)copper(II)

In the title complex, [CuCl2(C6H7N)2(CH3OH)], the copper atom is five-coordinated by two nitro-gen atoms of 2-methyl-pyridine ligands, two chloro ligands and an oxygen atom of the methanol mol-ecule, being in a tetra-gonal-pyramidal environment with N and Cl atoms forming the basal plane. In the crystal, complex mol-ecules related by the twofold rotation axis are joined into dimeric units by pairs of O-H⋯Cl hydrogen bonds. These dimeric units are assembled through C-H⋯Cl inter-actions into layers parallel to (001).

Synthesis and structure-activity relationships of quinolinone and quinoline-based P2X7 receptor antagonists and their anti-sphere formation activities in glioblastoma cells

Screening a compound library of quinolinone derivatives identified compound 11a as a new P2X7 receptor antagonist. To optimize its activity, we assessed structure-activity relationships (SAR) at three different positions, R₁, R₂ and R₃, of the quinolinone scaffold. SAR analysis suggested that a carboxylic acid ethyl ester group at the R₁ position, an adamantyl carboxamide group at R₂ and a 4-methoxy substitution at the R₃ position are the best substituents for the antagonism of P2X7R activity. However, because most of the quinolinone derivatives showed low inhibitory effects in an IL-1β ELISA assay, the core structure was further modified to a quinoline skeleton with chloride or substituted phenyl groups. The optimized antagonists with the quinoline scaffold included 2-chloro-5-adamantyl-quinoline derivative (16c) and 2-(4-hydroxymethylphenyl)-5-adamantyl-quinoline derivative (17k), with IC₅₀ values of 4 and 3 nM, respectively. In contrast to the quinolinone derivatives, the antagonistic effects of the quinoline compounds (16c and 17k) were paralleled by their ability to inhibit the release of the pro-inflammatory cytokine, IL-1β, from LPS/IFN-γ/BzATP-stimulated THP-1 cells (IC₅₀ of 7 and 12 nM, respectively). In addition, potent P2X7R antagonists significantly inhibited the sphere size of TS15-88 glioblastoma cells.

Comparative conformational analyses and molecular dynamics studies of glycylglycine methyl ester and glycylglycine N-methylamide

Amide–ester substitution and water models significantly alter conformational and solvation properties of glycine–glycine dipeptides.

Nanomolar Level Detection of Uric Acid in Blood Serum and Pest-Infested Grain Samples by an Amphiphilic Probe

A pyrene based amphiphilic receptor has been utilized in the nanomolar detection of uric acid at physiological pH in water. The compound shows a unique concentration-dependent modulation in optical response toward uric acid. In intramolecular/static excimer form (low concentration range), it displays a ratiometric response, while a "turn-off" sensing is observed specifically in the presence of intermolecular/dynamic excimer (high concentration range). The present protocol is then employed for the estimation of uric acid in blood serum samples of healthy individuals. Bland-Altman analysis in comparison to clinically approved uricase assay indicated the high accuracy of the present method. Additionally, the extent of insect infestation in stored grain samples was determined by measuring the uric acid content of their aqueous extracts. Low-cost color strips were developed for on-site detection of uric acid without involving any sophisticated instrument or trained personnel.

Conformational analysis of helical aminoisobutyric acid (Aib) oligomers bearing C-terminal ester Schellman motifs

The effect of Schellman motifs on the adoption of stable 310 helical conformations in a series of aminoisobutyric (Aib) oligomers has been studied in the solid state and solution. The destabilising effect of the Schellman motif (a local inversion of helical screw-sense due to a C-terminal ester residue) was quantified in the solid state using X-ray crystallography through analysis of the torsion angles and their deviation from those observed in an ideal 310 helix. Investigation of the intramolecular hydrogen-bonding interactions in the solid state led to the identification of a fully extended C5 conformation in one oligomer, which is a novel folding motif for Aib oligomers. The effect of ester groups with differing steric demands on intermolecular hydrogen-bonding contacts in the solid state was also ascertained. In solution, the adoption of a 310 conformation in Aib oligomers appeared to be more finely tuned, depending on a number of factors, including chain length and the steric demands of the C-terminal destabilising Schellman motif.

Synthesis of hybrid hydrazino peptides: protected vs unprotected chiral α-hydrazino acids

Peptidomimetics based on hydrazino derivatives of α-amino acids represent an important class of peptidic foldamers with promising biological activities, like protease inhibition and antimicrobial activity. However, the lack of straightforward method for the synthesis of optically pure hydrazino acids and efficient incorporation of hydrazino building blocks into peptide sequence hamper wider exploitation of hydrazino peptidomimetics. Here we described the utility of N^α-benzyl protected and unprotected hydrazino derivatives of natural α-amino acids in synthesis of peptidomimetics. While incorporation of N^α-benzyl-hydrazino acids into peptide chain and deprotection of benzyl moiety proceeded with difficulties, unprotected hydrazino acids allowed fast and simple construction of hybrid peptidomimetics.

Melt-processable dynamic-covalent poly(hemiaminal) organogels as scaffolds for UV-induced polymerization

Hemiaminal poly(ethylene glycol) (PEG)-based organogels are formulated in polymerizable solvents. The dynamic-covalent nature of the solvent-H-bonded hemiaminal crosslinks, together with the modification of the crosslinking density of the organogels allows for temperature-dependent viscoelastic control. The shape of uncured gels can be permanently retained by templated UV-curing of the solvent, offering great promise for complex manufacturing, printing, sealants, and materials repair.

Synthetic turn mimetics and hairpin nucleators: Quo Vadimus?

Structural mimicry of peptides has witnessed perceptible progress in the last three decades. Reverse turn and β-hairpin units are the smallest secondary structural motifs that are some of the most scrutinized functional cores of peptides and proteins. The practice of mimicking, without altering the function of the bioactive core, ranges from conformational locking of the basic skeleton to total replacement of structural architecture using synthetic analogues. Development of heterogeneous backbones--using unnatural residues in place of natural ones--has broadened further opportunities for efficient structural rigidification. This feature article endeavours to trail the path of progress achieved hitherto and envisage the possibilities that lie ahead in the development of synthetic turn mimetics and hairpin nucleators.