Triazolyl-donor-acceptor chromophore-decorated unnatural amino acids and peptides: FRET events in a β-turn conformation

N-Arylated peptide: troponyl residue influences the structure and conformation of N-troponylated-(di/tri)-peptides

N-arylated peptides as peptoids influence the structural and conformational changes of small peptides that lead to unique foldamers, even in di-/tri-peptides.

An explicitly designed paratope of amyloid-β prevents neuronal apoptosis in vitro and hippocampal damage in rat brain

Synthetic antibodies hold great promise in combating diseases, diagnosis, and a wide range of biomedical applications. However, designing a therapeutically amenable, synthetic antibody that can arrest the aggregation of amyloid-β (Aβ) remains challenging. Here, we report a flexible, hairpin-like synthetic paratope (SP1, ∼2 kDa), which prevents the aggregation of Aβ monomers and reverses the preformed amyloid fibril to a non-toxic species. Structural and biophysical studies further allowed dissecting the mode and affinity of molecular recognition events between SP1 and Aβ. Subsequently, SP1 reduces Aβ-induced neurotoxicity, neuronal apoptosis, and ROS-mediated oxidative damage in human neuroblastoma cells (SH-SY5Y). The non-toxic nature of SP1 and its ability to ameliorate hippocampal neurodegeneration in a rat model of AD demonstrate its therapeutic potential. This paratope engineering module could readily implement discoveries of cost-effective molecular probes to nurture the basic principles of protein misfolding, thus combating related diseases.

Multipurpose isothiocyanyl alanine/lysine: Use as solvatochromic IR probes and in site specific labeling/ligation of short peptides

The solvatochromic IR responsivity of small side chain -NCS in two unexplored unnatural amino acids, isothiocyanyl alanine (^NCSAla = Ita) and lysine (^NCSLys = Itl), without perturbing the conformation is demonstrated in two designed short tripeptide (BocAla-^NCSAla-Ala-OMe) and hexapeptide (BocLeu-Val-Phe-Phe-^NCSLys-Gly-OMe). Demonstration of site specific fluorescent labeling in both the peptides and ligation type reaction in ^NCSLys indicates the novelty of these two amino acids as alternative to the available canonical amino acids.

Uracil-amino acid as a scaffold for β-sheet peptidomimetics: Study of photophysics and interaction with BSA protein

We report herein the uracil-di-aza-amino acid (U^rAA) as a new family of molecular scaffold to induce β-hairpin structure with H-bonded β-sheet conformation in a short peptide. This has been demonstrated in two conceptual fluorescent pentapeptides wherein triazolylpyrenyl alanine and/or triazolylmethoxynapthyl alanine (^TPyAla_Do and/or ^TMNapAla_Do) are embedded into two arms of the uracil-amino acid via an intervening leucine. Conformational analysis by CD, IR, variable temperature and 2D NMR spectroscopy reveals the β-hairpin structures for both the peptides. Study of photophysical property reveals that the pentapeptide containing fluorescent triazolyl unnatural amino acids ^TMNapAla_Do and ^TPyAla_Do at the two termini exhibits dual path entry to exciplex emission-either via FRET from ^TMNapAla_Do to ^TPyAla_Do or via direct excitation of a FRET acceptor, ^TPyAla_Do. The other pentapeptide with ^TPyAla_Do/^TPyAla_Do pair shows excimer emission. Furthermore, both the peptides maintaining their fundamental photophysics are found to interact with BSA as only a test biomolecule.

Isothiocyanyl Alanine as a Synthetic Intermediate for the Synthesis of Thioureayl Alanines and Subsequent Aminotetrazolyl Alanines

The synthesis of unnatural amino acids with small side-chain functionalities usable for further transformations is highly demanding for the expansion of the genetic code and other possible biotechnological applications. To this end, we wanted to report the utility of an unexplored unnatural amino acid, isothiocyanyl alanine (^NCSAla = Ita), for the synthesis of another class of unnatural amino acids, thioureayl alanines (^TUAla = Tua). The synthesis of a third class of unnatural amino acids, amino tetrazolyl alanines (^ATzAla = Ata), in a very good yield was subsequently achieved utilizing thioureayl alanines. Thus, a variety of aliphatic- and aromatic-substituted thioureayl alanines and aromatic-substituted amino tetrazolyl alanines were successfully synthesized in good to excellent yields. The photophysical properties of three of the fluorescent unnatural amino acids from two classes were also studied and presented herein.

Axially chiral amino acid scaffolds as efficient fluorescent discriminators of methanol–ethanol

Differential solvation guided H-bonding interaction allows novel axially chiral amino acid scaffolds for efficient discrimination of ethanol–methanolviaa switch-on fluorescence response.

Trichromophoric pentapeptide: impact of β-sheet conformation on dual path to excimer emission and sensing of BSA

We established dual mechanisms for excimer emission-either via FRET or direct excitation of a FRET acceptor- in a conceptually novel trichromophoric pentapeptide which serves as an effective fluorescence light-up probe for protein–peptide interaction.

N-2-Aryl-1,2,3-Triazoles: A Novel Class of Blue Emitting Fluorophores-Synthesis, Photophysical Properties Study and DFT Computations

Novel fluorescent 2-[4-(4,5-diphenyl-1H-imidazol-2-yl) phenyl]-2H-naphtho [1,2-d] [1,2,3] triazolyl derivatives were synthesized from 4-(4,5-diphenyl-1H-imidazol-2-yl) aniline and substituted naphthalen-2-amine. The photophysical properties of the three new fluorophores were evaluated in acetonitrile, methanol, dimethylsulfoxide and N,N-dimethylformamide solvents and were compared with the reported analogs. The compounds show the absorption in the ultraviolet region and the emission in the blue region. The thermal stabilities of these compounds was evaluated by thermogravimetric analysis. The solvatochromism data are used for ground and excited state dipole moment determination of the synthesized triazoles using Bakhshiev and Bilot-Kawski correlations. The experimental absorption and emission were compared with the theoretical data obtained by DFT and TD-DFT computations and they are well in agreement with each other.

Triazolo-β-aza-ε-amino acid and its aromatic analogue as novel scaffolds for β-turn peptidomimetics

Triazolo-β-aza-ε-amino acid and its aromatic analogue (AlTAA/ArTAA) in the peptide backbone mark a novel class of conformationally constrained molecular scaffolds to induce β-turn conformations. This was demonstrated in a Leu-enkephalin analogue and in other designed peptides.