Regioselective fluorescent labeling of N,N,N-trimethyl chitosan via oxime formation

Toward tryptathionine-stapled one-bead-one-compound (OBOC) libraries: solid phase synthesis of a bioactive octretoate analog

New somatostatin analogs are highly desirable for diagnosing and treating neuroendocrine tumors (NETs). Here we describe the solid-phase synthesis of a new octreotate (TATE) analog where the disulfide bond is replaced with a tryptathionine (Ttn) staple as part of an effort to prototyping a one-bead-one-compound (OBOC) library of Ttn-stapled peptides. Library design provides the potential for on- and off-bead screening. To validate our method, we labelled Ttn-TATE with a fluorescent dye to demonstrate binding to soluble somatostatin receptor subtype-2 and staining of Ar42J rat prostate cancer cells. By exploring this staple in the context of a ligand of known affinity, this method paves the way for an OBOC library construction of bioactive octreotate analogs and, more broadly speaking, tryptathionine-staped peptide macrocycles.

Biological Synergy and Antimicrobial Mechanism of Hydroxypropyltrimethyl Ammonium Chloride Chitosan with Benzalkonium Chloride

Preservatives in eye drops have always been the focus of people's attention. Benzalkonium chloride (BAC) is one of the most frequently used bacteriostatic agents in eye drops, which has broad-spectrum and efficient bactericidal ability. However, the inappropriate dosage of BAC may lead to high cytotoxicity. Therefore, adding low-toxic hydroxypropyltrimethyl ammonium chloride chitosan (HACC) can not only achieve antimicrobial effect, but also have the advantages of moisturizing and biocompatibility. In this paper, the minimum inhibitory concentrations (MICs) of HACC and BAC were evaluated against Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis, Diphtheroid bacillus and Candida albicans. Based on the MIC of each antimicrobial agent, an antimicrobial assay was performed to investigate the antimicrobial ability of disinfectant solution. Besides, cytotoxicity had also been assessed. When the HACC/BAC solution at weight ratio of 150/1 showed a highest antimicrobial efficiency and the cell proliferation rates were the highest in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Furthermore, the cell leakage was examined by UV absorption, indicating the great synergistic antimicrobial effect between HACC and BAC. What is more, the results of micromorphology research suggested that as the result of repulsive force between the two molecules, the average particle size of HACC would decrease. Finally, the impedance experiment showed that with the addition of BAC, current density would increase significantly, suggesting that more positive charge group was exposed to aqueous solution, leading the the increase of antimicrobial ability. Based on these results, HACC-BAC combination solution might be a promising novel antimicrobial group for biomedical applications.

Development of Multifunctional Biopolymeric Auto-Fluorescent Micro- and Nanogels as a Platform for Biomedical Applications

The emerging field of theranostics for advanced healthcare has raised the demand for effective and safe delivery systems consisting of therapeutics and diagnostics agents in a single monarchy. This requires the development of multi-functional bio-polymeric systems for efficient image-guided therapeutics. This study reports the development of size-controlled (micro-to-nano) auto-fluorescent biopolymeric hydrogel particles of chitosan and hydroxyethyl cellulose (HEC) synthesized using water-in-oil emulsion polymerization technique. Sustainable resource linseed oil-based polyol is introduced as an element of hydrophobicity with an aim to facilitate their ability to traverse the blood-brain barrier (BBB). These nanogels are demonstrated to have salient features such as biocompatibility, stability, high cellular uptake by a variety of host cells, and ability to transmigrate across an in vitro BBB model. Interestingly, these unique nanogel particles exhibited auto-fluorescence at a wide range of wavelengths 450-780 nm on excitation at 405 nm whereas excitation at 710 nm gives emission at 810 nm. In conclusion, this study proposes the developed bio-polymeric fluorescent micro- and nano- gels as a potential theranostic tool for central nervous system (CNS) drug delivery and image-guided therapy.

Glycoconjugate Oxime Formation Catalyzed at Neutral pH: Mechanistic Insights and Applications of 1,4-Diaminobenzene as a Superior Catalyst for Complex Carbohydrates

The reaction of unprotected carbohydrates with aminooxy reagents to provide oximes is a key method for the construction of glycoconjugates. Aniline and derivatives serve as organocatalysts for the formation of oximes from simple aldehydes, and we have previously reported that aniline also catalyzes the formation of oximes from the more complex aldehydes, carbohydrates. Here, we present a comprehensive study of the effect of aniline analogues on the formation of carbohydrate oximes and related glycoconjugates depending on organocatalyst structure, pH, nucleophile, and carbohydrate, covering more than 150 different reaction conditions. The observed superiority of the 1,4-diaminobenzene (PDA) catalyst at neutral pH is rationalized by NMR analyses and DFT studies of reaction intermediates. Carbohydrate oxime formation at pH 7 is demonstrated by the formation of a bioactive glycoconjugate from a labile, decorated octasaccharide originating from exopolysaccharides of the soil bacterium Mesorhizobium loti. This study of glycoconjugate formation includes the first direct comparison of aniline-catalyzed reaction rates and equilibrium constants for different classes of nucleophiles, including primary oxyamines, secondary N-alkyl oxyamines, as well as aryl and arylsulfonyl hydrazides. We identified 1,4-diaminobenzene as a superior catalyst for the construction of oxime-linked glycoconjugates under mild conditions.

Characteristics of cricket (Gryllus bimaculatus) chitosan and chitosan-based nanoparticles

The field cricket (Gryllus bimaculatus) is commonly consumed as food in different parts of the world. This study was performed to characterize the chitosan extracted from crickets and to assess its potential use to the growing functional market. The degree of deacetylation (DA), Fourier-transform infrared spectra, X-ray diffraction patterns, molecular mass, scanning electron microscopy spectra, and color were measured. Cricket chitosan nanoparticles were prepared, and the optimal conditions were identified. The molecular mass of the cricket chitosan was lower than that of commercial chitosan; however, the DA, FTIR, and XRD spectra were similar. The particle size (208.27 ± 3.47 nm), zeta potential (35.72 ± 1.29 mV), and polydispersity index (PDI: 0.27 ± 0.03) of the cricket chitosan NPs were superior to the commercial. Addition of NaCl reduced the cricket chitosan NPs size up to 15.5%. This finding is a novel trial to prove the availability of the insect chitosan with a low molecular mass as an active carrier source.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Endosome Targeting meso-Tetraphenylchlorin-Chitosan Nanoconjugates for Photochemical Internalization

Four amphiphilic covalently linked meso-tetraphenylchlorin-chitosan nanoconjugates were synthesized and evaluated for use in photochemical internalization (PCI) in vitro and in vivo. The synthetic protocol for the preparation of two different hydrophobic chlorin photosensitizers, 5-(4-aminophenyl)-10,15,20-triphenylchlorin and 5-(4-carboxyphenyl)-10,15,20-triphenylchlorin, was optimized. These monofunctional photosensitizers were covalently attached to carrier chitosan via silyl-protected 3,6-di-O-tert-butyldimethylsilyl-chitosan (Di-TBDMS-chitosan) with 0.10 degree of substitution per glucosamine (DS). Hydrophilic moieties such as trimethylamine and/or 1-methylpiperazine were incorporated with 0.9 DS to give fully water-soluble conjugates after removal of the TBDMS groups. A dynamic light scattering (DLS) study confirmed the formation of nanoparticles with a 140-200 nm diameter. These nanoconjugates could be activated at 650 nm (red region) light, with a fluorescence quantum yield (Φ_F) of 0.43-0.45, and are thus suitable candidates for use in PCI. These nanoconjugates were taken up and localized in the endocytic vesicles of HCT116/LUC human colon carcinoma cells, and upon illumination they substantially enhanced plasmid DNA transfection. The nanoconjugates were also evaluated in preliminary in vivo experiments in tumor-bearing mice, showing that the nanoconjugates could induce a strong photodynamic therapy (PDT) and also PCI effects in treatment with bleomycin.

Regioselective chitosan end-group activation: the triskelion approach

Non-reactive chitosan extremities are regioselectively activated with a trivalent linker, called triskelion, allowing subsequent end-group functionalization with any thiol-reactive species.

Regioselective thioacetylation of chitosan end-groups for nanoparticle gene delivery systems

Chitosan (CS) end-group chemistry is a conjugation strategy that has been minimally exploited in the literature to date. Although the open-chain form of the CS reducing extremity bears a reactive aldehyde moiety, the most common method to generate a reactive end-group on CS is nitrous acid depolymerization, which produces a 2,5-anhydro-d-mannose unit (M-Unit) bearing also an aldehyde moiety. However, the availability of the latter might be low, since previous literature suggests that its hydrated and non-reactive form, namely the gem-diol form, is predominant in acidic aqueous conditions. Oxime-click chemistry has been used to react on such aldehydes with various degrees of success, but the use of a co-solvent and additional chemical reagents remain necessary to obtain the desired and stable covalent linkage. In this study, we have assessed the availability of the aldehyde reactive form on chitosan treated with nitrous acid. We have also assessed its reactivity towards thiol-bearing molecules in acidic conditions where CS amino groups are fully protonated and thus unreactive towards aldehyde. LC-MS and NMR spectroscopy methods (1H and DOSY, respectively) confirmed the regioselective thioacetylation of the reactive aldehyde with conversion rates between 55 and 70% depending on the thiol molecule engaged. The stabilization of the hemithioacetal intermediates into the corresponding thioacetals was also found to be facilitated upon freeze-drying of the reaction medium. The PEGylation of the CS M-Unit aldehyde by thioacetylation was also performed as a direct application of the proposed conjugation approach. CS-b-PEG2 block copolymers were successfully synthesized and were used to prepare block ionomer complexes with plasmid DNA, as revealed by their spherical morphology vs. the rod-like/globular/toroidal morphology observed for polyplexes prepared using native unmodified chitosan. This novel aqueous thiol-based conjugation strategy constitutes an alternative to the oxime-click pathway; it could be applicable to other polymers.

Rapid End-Group Modification of Polysaccharides for Biomaterial Applications in Regenerative Medicine

Polysaccharides have emerged as important functional materials because of their unique properties such as biocompatibility, biodegradability, and availability of reactive sites for chemical modifications to optimize their properties. The overwhelming majority of the methods to modify polysaccharides employ random chemical modifications, which often improve certain properties while compromising others. On the other hand, the employed methods for selective modifications often require excess of coupling partners, long reaction times and are limited in their scope and wide applicability. To circumvent these drawbacks, aniline-catalyzed oxime formation is developed for selective modification of a variety of polysaccharides through their reducing end. Notably, it is found that for efficient oxime formation, different conditions are required depending on the composition of the specific polysaccharide. It is also shown how our strategy can be applied to improve the physical and functional properties of alginate hydrogels, which are widely used in tissue engineering and regenerative medicine applications. While the randomly and selectively modified alginate exhibits similar viscoelastic properties, the latter forms significantly more stable hydrogel and superior cell adhesive and functional properties. Our results show that the developed conjugation reaction is robust and should open new opportunities for preparing polysaccharide-based functional materials with unique properties.