Solid-phase Synthesis Research Articles

Molecular Programming Design of Glyconucleic Acid Aptamer with High Stability.

Functional nucleic acids (FNAs), possessing specific biological functions beyond their informational roles, have gained widespread attention in disease therapeutics. However, their clinical application is severely limited by their low serum stability in complex physiological environments. In this work, a precise molecular programming strategy is explored to prepare glyconucleic acid aptamers (GNAAs) with high serum stability. Four glyconucleic acid modules compatible with commercial solid-phase synthesis are designed and synthesized. Through precise molecular design, the accurate modification of four different carbohydrate ligands at specific sites of DNA aptamers is achieved. It is demonstrated that glycosylation modification can significantly increase DNA aptamers' serum stability while maintaining their structures and high affinity. The stabilization effect is superior to that of currently commonly used commercial chemical modifications. Moreover, it is confirmed that this approach displays insignificant effects on the DNA aptamers' tumor-targeting ability and metabolism in vivo. This method offers a simple, economical, and efficient strategy for precise glycosylation modification of nucleic acids. This allows to prepare glycosyl functional nucleic acids with high serum stability, which can expand the application scope of functional nucleic acids and promote the practical transformation of functional nucleic acids.

Spiropyran as Building Block in Peptide Synthesis and Modulation of Photochromic Properties.

Light-controlled triggering of materials requires efficient embedding of molecular photoswitches into larger molecules. We herein present the synthesis of two new building blocks for the synthesis of photoswitchable peptides, embedding spiropyranes as a central unit into peptide-backbones via a novel, yet unreported approach. The synthesis presented here allows us to embed spiropyranes directly into solid-phase peptide synthesis (SPPS), further describing the resulting photophysical properties of the as-prepared photoswitchable peptides.

Stabilizing Scaffold for Short Peptides Based on Knottins.

Bombesin (BBN) is a short peptide with a high affinity for receptors that are expressed on the surface of various types of cancer cells. However, a full length BBN molecule has low in vivo stability. In our study, we propose the use of peptide toxins, derived from animal and plant toxins, as scaffold molecules to enhance the bioavailability and stability of bombesin. These peptides possess a unique structure known as an inhibitory cystine knot. We synthesized structures in which short bombesin was incorporated into various domains of arthropod and plant toxins using solid-phase peptide synthesis. The stability under different conditions was assessed through high-performance liquid chromatography, and binding to cell cultures expressing the bombesin receptor was analyzed. Additionally, toxicity to cell cultures was evaluated using fluorescence microscopy. The data obtained demonstrated that placing the short peptide between the first and second cysteine residues in arachnid toxins results in increased in vitro stability and bioavailability, as well as low cytotoxicity. Arachnid toxins with an inhibitory cystine knot can be considered as a scaffold for increasing the stability of therapeutic peptides.

Prediction and Validation of Proline-containing Tripeptides with Angiotensin I-converting Enzyme Inhibitory Activity Using Machine Learning Models

Background: Numerous inhibitory peptides against angiotensin I-converting enzyme, a target for hypertension treatment, have been found in previous studies. Recently, machine learning screening has been employed to predict unidentified inhibitory peptides using a database of known inhibitory peptides and descriptor data from docking simulations. Objective: The aim of this study is to focus on angiotensin I-converting enzyme inhibitory tripeptides containing proline, to predict novel inhibitory peptides using the machine learning algorithm PyCaret based on their IC50 and descriptors from docking simulations, and to validate the screening method by machine learning by comparing the results with in vitro inhibitory activity studies. Methods: IC50 of known inhibitory peptides were collected from an online database, and descriptor data were summarized by docking simulations. Candidate inhibitory peptides were predicted from these data using the PyCaret. Candidate tripeptides were synthesized by solid-phase synthesis and their inhibitory activity was measured in vitro. Results: Seven novel tripeptides were found from the peptides predicted to have high inhibitory activity by machine learning, and these peptides were synthesized and evaluated for inhibitory activity in vitro. As a result, the proline-containing tripeptide MPA showed high inhibitory activity, with an IC50 value of 8.6 µM. Conclusion: In this study, we identified a proline-containing tripeptide with high ACE inhibitory activity among the candidates predicted by machine learning. This finding indicates that the method of predicting by machine learning is promising for future inhibitory peptide screening efforts.

Solid-Phase Synthesis of Poly(imino anthraquinone)s for Low-Cost and High-Performance Bipolar Organic Cathode Materials.

Organic polymer cathode materials have emerged as promising candidates for constructing sustainable lithium and post-lithium batteries. However, it remains a significant challenge to synthesize electroactive polymers with the desired energy density and cycling stability in a cost-effective manner. Herein, we present a simple yet effective solid-phase method for synthesizing a series of bipolar quinone-amine polymers, specifically, poly(imino anthraquinone)s (PIAQs). The dehydration polycondensation reaction, occurring at 350 °C between the amino and hydroxy groups of low-cost diaminoanthraquinone and dihydroxyanthraquinone monomers, yields four PIAQ samples with identical repeating units but varied connection patterns. As cathode materials for lithium batteries employing ester-type electrolytes, they exhibit comparable charge-discharge curves and energy densities within 1.5-4.3 V but varying cycling stabilities proportional to their polymerization degrees. For example, despite its lowest-cost monomers, PIAQ-44 demonstrates one of the most outstanding electrochemical performances among polymer cathode materials, boasting a reversible capacity of 248 mA h g-1, an average discharge voltage of 2.53 V, and a high cycling stability (75% capacity retention after 2000 cycles). Moreover, the slight differences in electrochemical performance among the four PIAQs, pertaining to bipolar redox, irreversible deprotonation, and capacity fade, have been thoroughly elucidated to provide constructive insights into quinone-amine polymers.

Bottlebrush Polymers with Sequence-Controlled Backbones for Enhanced Oligonucleotide Delivery.

The clinical translation of oligonucleotide-based therapeutics continues to encounter challenges in delivery. In this study, we introduce a novel class of delivery vehicles for oligonucleotides that are based on poly(ethylene glycol) (PEG) bottlebrush polymers with sequence-defined backbones. Using solid-phase synthesis and bespoke phosphoramidites, the oligonucleotide and the polymer backbone can be assembled on the solid support. The synthesis allows chemical modifiers such as carbon 18 (C18) units to be incorporated into the backbone in specific patterns to modulate the cell-material interactions. Subsequently, PEG side chains were grafted onto the polymer segment of the resulting polymer-oligonucleotide conjugate, yielding bottlebrush polymers. We report an optimal pattern of the C18 modifier that leads to improved cellular uptake, plasma pharmacokinetics, biodistribution, and antisense activity in vivo. Our results provide valuable insights into the structure-property relationship of polymer-oligonucleotide conjugates and suggest the possibility of tuning the polymer backbone to meet the specific delivery requirements of various diseases.

Syngas Production by Fe2SiO4 Oxygen Carrier in Chemical Looping Partial Oxidation of Methane

Chemical looping partial oxidation of methane (CLPOM) is a low energy consumption and environmentally friendly new technology that can generate syngas. The main challenge is to find suitable oxygen carriers, which should be highly active, stable, low cost, and eco-friendly. This study found that Fe2SiO4 had good reactivity in the CLPOM process. Thermodynamic calculations were carried out by FactSage8.1 to demonstrate the feasibility of Fe2SiO4 as an oxygen carrier for CLPOM. Fe2SiO4 was prepared by the direct ball milling method and the high-temperature solid-phase synthesis method. The reaction properties of Fe2SiO4 were investigated in the fixed bed reactor. The XRD and FTIR results indicate that Fe2SiO4 can be synthesized successfully through the high-temperature solid-phase synthesis method. The results of fixed bed experiments showed that when the reaction temperature was 980 °C and the reaction time was 28 min, the XCH4 reached 87%, and the SH2 and SCO were 70% and 71%, respectively. Subsequently, 20 redox cycle experiments were conducted under the optimal reaction conditions. The results showed that Fe2SiO4 exhibited good reactivity in the first two cycles, and as the reaction progressed, the reduced oxygen carrier could not regain the lattice oxygen, leading to a decline in cyclic performance. This study demonstrates that Fe2SiO4 can couple CO2 and CH4 to produce syngas and is conducive to reducing carbon emissions.

Extraction, purification, and mechanism of immunomodulatory peptides obtained from silkworm pupa protein hydrolysate

Silkworm pupa, a by-product of silk reeling, is rich in protein; however, it has traditionally been used as animal feed. This study isolated and purified peptides from the enzymatic hydrolysates of silkworm pupa protein, thus effectively enhancing its utilization. The immune activity of these peptides was evaluated in macrophages, and 609 peptides were identified using LC-MS/MS. These active peptides were screened based on their toxicity, allergenic, and biological activity, and their interactions with TLR2 and TLR4/MD-2 were predicted via molecular docking. Results indicated that APFAPAPL, YLPPFNSF, and FIPNEAFAGRPF could strongly bind to TLR2 and TLR4/MD-2 through hydrogen bonding and hydrophobic interactions. These peptides were synthesized using solid-phase synthesis, and their immune activity was verified by proliferation, NO, ROS and TNF-α secretion assays. All three peptides promoted the proliferation, phagocytosis, and secretion of ROS and TNF-α by macrophages. Western blot analysis showed that the peptides activated RAW 264.7 cells via the NF-κB and MAPK signaling pathways, mediated by TLR2 and TLR4/MD-2 receptors. Therefore, this study provides a new understanding of the immunomodulatory activity of silkworm pupa proteins, implying their potential use as functional food ingredients.

Stereorandomized Oncocins with Preserved Ribosome Binding and Antibacterial Activity.

We recently showed that solid-phase peptide synthesis using racemic amino acids yields stereorandomized peptides comprising all possible diastereomers as homogeneous, single-mass products that can be purified by HPLC and that stereorandomization modulates activity, toxicity, and stability of membrane-disruptive cyclic and linear antimicrobial peptides (AMPs) and dendrimers. Here, we tested if stereorandomization might be compatible with target binding peptides with the example of the proline-rich AMP oncocin, which inhibits the bacterial ribosome. Stereorandomization of up to nine C-terminal residues preserved ribosome binding and antibacterial effects including activities against drug-resistant bacteria and protected against serum degradation. Surprisingly, fully stereorandomized oncocin was as active as L-oncocin in dilute growth media stimulating peptide uptake, although it did not bind the ribosome, indicative of an alternative mechanism of action. These experiments show that stereorandomization can be compatible with target binding peptides and can help understand their mechanism of action.

Ultra-Selective and Sensitive Fluorescent Chemosensor Based on Phage Display-Derived Peptide with an N-Terminal Cu(II)-Binding Motif.

Copper, along with gold, was among the first metals that humans employed. Thus, the copper pollution of the world's water resources is escalating, posing a significant threat to human health and aquatic ecosystems. It is crucial to develop detection technology that is both low-cost and feasible, as well as ultra-selective and sensitive. This study explored the use of the NH2-Xxx-His motif-derived peptide from phage display technology for ultra-selective Cu2+ detection. Various Cu-binding M13 phage clones were isolated, and their affinity and cross-reactivity for different metal ions were determined. A detailed analysis of the amino acid sequence of the unique Cu-binding peptides was employed. For the development of an optical chemosensor, a peptide with an NH2-Xxx-His motif was selected. The dansyl group was incorporated during solid-phase peptide synthesis, and fluorescence detection assays were employed. The efficacy of the Cu2+-binding peptide was verified through spectroscopic measurements. In summary, we developed a highly selective and sensitive fluorescent chemosensor for Cu2+ detection based on a peptide sequence from a phage display library that carries the N-terminal Xxx-His motif.

A novel androgen-independent radiotracer with dual targeting of NTSR1 and PSMA for PET/CT imaging of prostate cancer

A substantial proportion of patients with prostate cancer (PCa) develop treatment resistance or mortality after androgen deprivation therapy (ADT). Current methods for identifying and locating recurrent lesions using prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET) imaging, which relies on androgen levels, often result in diagnostic delays. Therefore, the development of an androgen-independent radiotracer is critical for the early identification of recurrent lesions. The neurotensin receptor 1 (NTSR1) is highly expressed in androgen-independent PCa lesions. Here, we synthesized a bispecific ligand targeting PSMA and NTSR1 by solid-phase peptide synthesis and formulated a68Ga-labeled bispecific radiotracer, ([68Ga]Ga-NT-PSMA). This radiotracer exhibited a high radiochemical yield (71.27 % ± 1.58 %) and demonstrated an affinity for NTSR1 (39.32 ± 2.98 nM) and PSMA (63.47 ± 5.14 nM) in vitro. Small animal PET imaging showed comparable uptake of [68Ga]Ga-NT-PSMA and the monomeric radiotracer [68Ga]Ga-DOTA-NT20.3 in mice bearing androgen-independent PC3 (3.64 ± 0.49 %ID/g vs. 5.60 ± 1.42 %ID/g, nonsignificant [ns]) and DU145 tumors (2.49 ± 0.20 %ID/g vs. 2.34 ± 0.18 %ID/g, ns) at 90 min post-injection. In androgen-dependent 22Rv1 xenografts, [68Ga]Ga-NT-PSMA uptake was lower (1.94 ± 0.29 %ID/g) than [68Ga]Ga-PSMA-11 (3.94 ± 0.26 %ID/g, P < 0.001). Nevertheless, [68Ga]Ga-NT-PSMA effectively imaged all three xenograft types with high contrast, an achievement not possible with monomeric radiotracers alone. These results indicate that imaging with [68Ga]Ga-NT-PSMA is independent of the androgen dependence of the model, highlighting its potential as a promising nuclear medicine diagnostic tool for the early identification and localization of castration-resistant PCa lesions.

Photo-Accelerated Synthesis of Oligo(triazole amide)s.

A photo-assisted process is explored for improving the synthesis of oligo(triazole amide)s, which are prepared by solid phase synthesis using a repeated cycle of two reactions: amine-carboxylic acid coupling and copper-catalyzed azide-alkyne cycloaddition (CuAAC). The improvement of the second reaction is investigated herein. A catalytic system involving Cu(II)Cl2, N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDETA)and a titanocene photoinitiator is explored for reducing the reaction time of CuAAC. This catalyst is first tested on a model reaction involving phenylacetylene and ethyl azidoacetate in DMSO. The kinetics of these model experiments are monitored by 1H NMR in the presence of different concentrations of the photoinitiator. It is found that 30 mol% of photoinitiator leads to quantitative reactions in only 8 min. These conditions are then applied to the solid phase synthesis of oligo(triazole amide)s, performed on a glycine-loaded Wang resin. The backbone of the oligomers is constructed using 6-heptynoic acid and 1-amino-11-azido-3,6,9-trioxaundecane as submonomers. Due to slow reagent diffusion, the CuAAC step required more time in the solid phase than in solution. Yet, one hour only is necessary to achieve quantitative CuAAC on the resin, which is twice as fast as previously-reported conditions. Using these optimized conditions, oligo(triazole amide)s of different length are prepared.

Properties of phosphoramide benzoazole oligonucleotides (PABAOs). II. Structure and hybridization efficiency of N-benzoxazole derivatives

New phosphate-modified nucleic acid derivatives are of great significance in basic research and biomedical applications. We have recently developed a new class of phosphoramide benzoazole oligonucleotides (PABAOs). In this work, th properties of N-benzoxazole oligodeoxyribonucleotides have been thoroughly examined. We have demonstrated the convenient automated solid-phase synthesis of oligomers with a different number of modifications (up to six) at various positions. Optical properties, thermal stability, structure, and dynamics of PABAO/DNA complexes have been investigated. The N-benzoxazole-modified phosphate group is uncharged at neutral pH and has a pKa value of 8.52. Structural analysis performed by the CD spectroscopy and MD simulation indicate B-form of PABAO/DNA duplexes. The thermal stability of PABAO/DNA complexes bearing N-benzoxazole is reduced by 2.5–6.2° per modification compared to native duplexes at standard and near physiological buffer conditions. The performed study underlines a great potential of phosphoramide benzoazole oligonucleotides for basic research, applied sciences, and biotechnology.

Study of the structure guide mechanism of solid phase synthesis of CAN zeolite from coal gasification slag and its fixation of the Cr6+ structure in wastewater

The generation of a large amount of coal gasification coarse slag (CGCS) restricts the sustainable development of the modern coal chemical industry. This paper uses CGCS as raw material, adopts a solid phase synthesis method, saves water resources, is a new method of synthesizing zeolite with low secondary pollution. Different types of anions were used to induce the synthesis of zeolites. Using XRD, FT-IR, 27Al-NMR, 29Si-NMR, BET, SEM, and experimental research methods, the activation and depolymerization of CGCS in the solid phase reaction and the guiding role of anions in crystal growth were studied. The results revealed that the anionic structure with triple rotational axis symmetry can induce the synthesis of single-phase CAN zeolite. Using this rule, CAN zeolite was synthesized using CGCS as raw material and Cr6+ containing wastewater with triple rotation axis symmetry as the structural guide agent, and Cr6+ in wastewater was structurally fixed. Compared to the adsorption effect of CGCS on Cr6+, the results showed that the synthesized CAN zeolite was found to effectively fix Cr6+ (74.98 mg/g) from wastewater, which was much higher than that of CGCS (24.85 mg/g).

Improved Large-Scale Synthesis of Acridonylalanine for Diverse Peptide and Protein Applications.

Fluorescent unnatural amino acids give biochemists, biophysicists, and bioengineers new ways to probe the properties of proteins and peptides. Here, the synthesis of acridon-2-ylalanine (Acd) is optimized for large-scale production to enable ribosomal incorporation through genetic code expansion (GCE), and fluorenylmethoxycarbonyl (Fmoc)-protected Acd is prepared for solid-phase peptide synthesis (SPPS). We demonstrate the utility of Acd in several applications: first, Acd quenching by Tyr is used in the design of fluorescent protease sensors made by SPPS. Second, we demonstrate Acd incorporation into a lanthanide-binding peptide that is generated either by GCE or by SPPS and demonstrate the utility of Acd for sensitizing the emission of Eu3+. Finally, Acd is inserted into the intrinsically disordered protein, α-synuclein, using GCE and used to study ion binding and aggregation.

Mullite Synthesis Using Porous 3D Structures Consisting of Nanofibrils of Aluminum Oxyhydroxide Chemically Modified with Ethoxysilanes

Nanocrystalline mullite was synthetized by annealing a highly porous 3D structure consisting of nanofibrous aluminum oxyhydroxides treated with ethoxysilanes. The chemical, structural, and phase transformations in the aluminosilicate nanosystem were studied in the temperature range between 100 and 1600 °C. The features of the solid-phase synthesis of mullite at the interface of crystalline alumina with a liquid silica layer are discussed. It was established that chemical modification of the alumina surface with ethoxysilanes significantly limits the interphase mass transport and delays the phase transformation of the amorphous oxide into γ-Al2O3, which begins at temperatures above 1000 °C, while the basic structural nanofibrils are already crystallized at ~850 °C. The formation of mullite was completed at temperatures ≥ 1200 °C, where the fraction of γ-Al2O3 sharply decreased.

Total Syntheses of Cyclomarin and Metamarin Natural Products.

The first total synthesis of the heptapeptide Cyclomarin A (CymA) was achieved via new routes to chiral amino acid building blocks (highlighted) and solid-phase peptide synthesis. A structurally misassigned epimer of CymA (CymA'), Cyclomarin C, and Metamarin were also synthesized. Affirmation of the syntheses was corroborated by observations that the synthetic molecules have antimicrobial activities mirroring those of the natural products. Interestingly, CymA' is more potent than CymA.

Enzymatic hydrolysis-assisted magnetic beads adsorption for precise localization of IgE-linear epitopes in ovalbumin and the mechanism of reduced allergenicity after enzymatic hydrolysis

We present a method for precisely localizing IgE-linear epitopes by adsorption of peptides containing IgE-linear epitopes onto magnetic beads. Optimal enzymatic hydrolysis conditions (55 °C, 40 min) were determined to disrupt the OVA structure, facilitating specific adsorption of peptides containing IgE-linear epitopes onto magnetic beads. Using Liquid-mass spectrometry, we identified fourteen peptides with IgE-linear epitopes, among which epitopes 3 (T91-F99), 4 (L124-F134), 6 (V160-D167), 9 (V243-E248), and 13 (S317-K322) were found to be high-frequency IgE-linear epitopes. Additionally, epitopes 1 (V41-Q52), 3 (T91-F99), 8 (Y212-A220), 11 (N292-V296), and 13 (S317-K322) were identified as previously unreported IgE-linear epitopes. Through solid-phase peptide synthesis, indirect competitive ELISA and molecular docking. The results showed that the above five peptides were mainly bound to MHC-II through hydrogen bonding. Among them, epitope 3 has the strongest affinity for MHC-II. In conclusion, magnetic beads adsorption of peptides containing IgE-linear epitopes was a novel method for the precise localization of IgE-linear epitopes. This technique was facile to execute and enables rapid and accurate identification of IgE-antigen binding sites.

Dielectric relaxation, crystal structure and magnetic phenomena in solid solutions based on alkali metal niobates and bismuth ferrite in a wide range of external influences

Solid solutions of the system (1-x)(Na0.5K0.5)NbO3-xBiFeO3 with 0.85 ≤ x ≤ 0.95 have been prepared by two-step solid phase synthesis followed by sintering using conventional ceramic technology. An experimental study of the crystal structure, dielectric spectra in a wide range of temperatures and frequencies of alternating electric field and magnetic phenomena was carried out. The correlation between crystal structure and macro-responses in the temperature range (300 - 800) K has been established. The formation of two relaxation processes of non-Debyev type in the studied solid solutions in the temperature range (529 - 720) K with activation energies of 0.135 eV and 0.329 eV was found.

Low-vanadium and high-activity SCR catalyst for low-temperature denitrification: Influence of vanadium precursor and surface vanadium concentration

Nitrogen oxides (NOx), as the main pollutants of air pollution, cause serious harm to the ecological environment and human health. SCR technology is widely used as the most effective method for treating NOx. The core of SCR technology is SCR catalyst. The reaction temperature of traditional commercial catalysts is difficult to reach the optimal operating temperature range, so expanding the temperature window of V2O5/TiO2 catalysts to the low-temperature region while reducing vanadium loading is a key issue to be solved. A series of V2O5/TiO2 catalysts with different vanadium precursors and different vanadium loadings were prepared by solid-phase synthesis method. The physicochemical properties of the catalyst were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed desorption of ammonia and temperature programmed reduction of hydrogen. The denitrification activity of the catalyst was evaluated in a fixed bed reactor. The catalysts prepared with vanadyl oxalate (VOC2O4·xH2O) and vanadyl acetylacetonate (VO(acac)2) as vanadium precursors with a vanadium loading of 5% exhibited the highest denitrification activity, with a stable NOx conversion of 100% within the temperature range of 200–350 °. Compared with the catalysts prepared with ammonium metavanadate (NH4VO3) and vanadyl sulfate (VOSO4·xH2O) as the vanadium precursors, the maximum activity temperature of VOC2O4-V5Ti and VO(acac)2-V5Ti shifted towards the low-temperature region by about 150 °. Furthermore, the denitrification activity of catalyst with a low vanadium content (1%) prepared using VO(acac)2 precursor was even higher than that of catalyst with a high vanadium content (6%) prepared using NH4VO3 precursor. Using VOC2O4 and VO(acac)2 as vanadium precursors could effectively regulate the active sites and polymeric states on the catalysts, and promote the interaction of V atoms with different valence states to form more reductive V species (V4+), thus exhibiting excellent SCR reactivity. This study provided an effective method for the preparation of low-vanadium and high-activity denitrification catalysts at low temperatures.