Synthesis of <em>N,N,N</em>-trimethyl chitosan homopolymer and highly substituted <em>N</em>-alkyl-<em>N,N</em>-dimethyl chitosan derivatives with the aid of di-<em>tert</em>-butyldimethylsilyl chitosan

A highly chemoselective strategy for the synthesis of N,N,N-trimethyl chitosan (TMC) homopolymer and highly substituted N-alkyl-N,N-dimethyl chitosan derivatives was achieved using di-tert-butyldimethylsilyl-3,6-O-chitosan (di-TBDMS chitosan) as a precursor. The influence of different solvents, reagents and other reaction conditions on the reduction, trimethylation and quaternization of these di-TBDMS chitosan derivatives was studied. Products were characterized by NMR after each step. Di-TBDMS chitosan was reacted with methyl iodide in NMP, giving a 100% substituted TMC with the trimethyl group appearing at 3.35 ppm in H-1 NMR spectrum. N-Propyl-, N-butyl- and N-hexyl-N,N-dimethyl chitosan derivatives were synthesized by stepwise reductive alkylation of di-TBDMS chitosan, followed by quaternization with dimethyl sulfate in dichloromethane, giving 65-72% substituted N-alkyl-N,N-dimethyl chitosan derivatives under optimized conditions. Analysis of these water-soluble chitosan derivatives by FT-IR, H-1 NMR, C-13 NMR, H-1-H-1 COSY and H-1-C-13 HSQC NMR enabled detailed structural characterization. All peaks could be assigned to N-modification, showing the selectivity of the di-TBDMS protection. (C) 2011 Elsevier Ltd. All rights reserved

The effect of substituent, degree of acetylation and positioning of the cationic charge on the antibacterial activity of quaternary chitosan derivatives.

To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files. This article is open access.A series of water-soluble cationic chitosan derivatives were prepared by chemoselective functionalization at the amino group of five different parent chitosans having varying degrees of acetylation and molecular weight. The quaternary moieties were introduced at different alkyl spacer lengths from the polymer backbone (C-0, C-2 and C-6) with the aid of 3,6-di-O-tert-butyldimethylsilyl protection of the chitosan backbone, thus allowing full (100%) substitution of the free amino groups. All of the derivatives were characterized using 1H-NMR, 1H-1H COSY and FT-IR spectroscopy, while molecular weight was determined by GPC. Antibacterial activity was investigated against Gram positive S. aureus and Gram negative E. coli. The relationship between structure and activity/toxicity was defined, considering the effect of the cationic group's structure and its distance from the polymer backbone, as well as the degree of acetylation within a molecular weight range of 7-23 kDa for the final compounds. The N,N,N-trimethyl chitosan with 100% quaternization showed the highest antibacterial activity with moderate cytotoxicity, while increasing the spacer length reduced the activity. Trimethylammoniumyl quaternary ammonium moieties contributed more to activity than 1-pyridiniumyl moieties. In general, no trend in the antibacterial activity of the compounds with increasing molecular weight or degree of acetylation up to 34% was observed.Icelandic Research Fund/20443023) Nordforsk Public Private Partnership, Genis ehf

Asymmetric Phenyl Substitution: An Effective Strategy to Enhance the Photosensitizing Potential of Curcuminoids

Curcumin has been demonstrated to exhibit photosensitized bactericidal activity. However, the full exploitation of curcumin as a photo-pharmaceutical active principle is hindered by fast deactivation of the excited state through the transfer of the enol proton to the keto oxygen. Introducing an asymmetry in the molecular structure through acting on the phenyl substituents is expected to be a valuable strategy to impair this undesired de-excitation mechanism competing with the therapeutically relevant ones. In this study, two asymmetric curcumin analogs were synthesized and characterized as to their electronic-state transition spectroscopic properties. Fluorescence decay distributions were also reconstructed. Their analysis confirmed the substantial stabilization of the fluorescent state with respect to the parent compound. Nuclear magnetic resonance experiments were performed with the aim of determining the structural features of the keto&ndash;enol ring and the strength of the keto&ndash;enol hydrogen bond. Electronic structure calculations were also undertaken to elucidate the effects of substitution on the features of the keto&ndash;enol semi-aromatic system and the proneness to proton transfer. Finally, their singlet oxygen-generation efficiency was compared to that of curcumin through the 9,10-dimethylanthracene fluorescent assay

Antibacterial phototoxic effects of synthetic asymmetric and glycosylated curcuminoids in aqueous formulations Studies on curcumin and curcuminoids. LIV

The aim of this study was to evaluate the in vitro phototoxic potential of synthetic asymmetric and glycosylated curcuminoids on planktonic model bacteria by counting the colony forming units. The Gram-positive Enterococcus faecalis and the Gram-negative Escherichia coli were exposed to aqueous solutions of the curcuminoids ( 64 2.5 \u3bcM) in the presence or absence of selected pharmaceutical excipients (Pluronic\uae F127, PEG 400 and HP\u3b3CD) in combination with a low irradiation dose (5 J/cm2). All the asymmetric curcuminoids, but only one of the glycosylated curcuminoids demonstrated substantial phototoxic effect on Enterococcus faecalis ( 65 4.7 log reduction). Only two of the asymmetric curcuminoids showed a moderate to low phototoxic effect on the more persistent Escherichia coli. This study emphasized that aromatic hydroxyl substituents in the para-position are important to maintain the phototoxic potential of curcuminoids independent of molecular symmetry. Glycosylation of the aromatic substituents resulted in a substantial loss in phototoxicity towards planktonic bacteria, an apparent change in the non-radiative S1-decay process and a weaker interaction with Pluronic\uae F127 compared to the non-glycosylated curcuminoids. The selected excipients Pluronic\uae F127, PEG 400 and HP\u3b3CD strongly influenced the phototoxic potential of the unsymmetrical, non-glycosylated compounds

Endotoxins affect bioactivity of chitosan derivatives in cultures of bone marrow-derived human mesenchymal stem cells.

To access publisher's full text version of this article. Please click on the hyperlink in Additional Links field.Biomaterials research has been expanding over the last decade, in part to provide improved medical devices for the treatment of orthopedic tissue injuries. In the quest to provide the best performance combined with low cost for medical implants, an increasing number of non-chemists have entered the field of biomaterials research without the profound knowledge of chemistry needed to understand the complex interaction mechanisms and characteristics of natural substances. Likewise, non-biologists often lack understanding when it comes to the presence of the contaminating biota frequently found in natural substances. This lack of knowledge by researchers in the field, combined with sensitive in vitro cell-based assays, can lead to inaccurate evaluation of biomaterials. Hence, there should be both an active effort to assemble multi-disciplinary teams and a genuine concern for the possible effects of contamination on in vitro assays. Here, we show that the presence of bacterial endotoxins in chitosan derivatives can result in false-positive results, profoundly altering product performance in in vitro assays. False-positive results through uncritical use of natural substances in vitro can be avoided by proper endotoxin testing and careful evaluation of cytokine secretion patterns.Technology Development Fund Icelandic Research Fund Landspitali University Hospital research fun

Drug-Loaded Photosensitizer-Chitosan Nanoparticles for Combinatorial Chemo- and Photodynamic-Therapy of Cancer

In this study we have developed biodegradable polymeric nanoparticles (NPs) containing the cytostatic drugs mertansine (MRT) or cabazitaxel (CBZ). The NPs are based on chitosan (CS) conjugate polymers synthesized with different amounts of the photosensitizer tetraphenylchlorin (TPC). These TPC–CS NPs have high loading capacity and strong drug retention due to π–π stacking interactions between the drugs and the aromatic photosensitizer groups of the polymers. CS polymers with 10% of the side chains containing TPC were found to be optimal in terms of drug loading capacity and NP stability. The TPC–CS NPs loaded with MRT or CBZ displayed higher cytotoxicity than the free form of these drugs in the breast cancer cell lines MDA-MB-231 and MDA-MB-468. Furthermore, light-induced photochemical activation of the NPs elicited a strong photodynamic therapy effect on these breast cancer cells. Biodistribution studies in mice showed that most of the TPC–CS NPs accumulated in liver and lungs, but they were also found to be localized in tumors derived from HCT-116 cells. These data suggest that the drug-loaded TPC–CS NPs have a potential in combinatory anticancer therapy and as contrast agents

Tetraphenylporphyrin Tethered Chitosan Based Carriers for Photochemical Transfection

Water-soluble amphiphilic chitosan nanocarriers tethered with the photosensitizer <i>meso</i>-tetraphenylporphyrin were synthesized in a seven-step procedure, starting from 3,6-di-<i>O</i>-<i>tert</i>-butyldimethylsilyl-chitosan and 5-(<i>p</i>-aminophenyl)-10,15,20-triphenylporphyrin. The lipophilic photosensitizer could be introduced in a quantitative and reproducible reaction to give either 0.1 or 0.25 degrees of substitution per glucosamine monomer. Fluorescence and NMR investigations revealed the dynamic structures of the carriers, which formed nanoparticles in aqueous solution with a core of π-stacked photosensitizers. These carriers can then unfold in the lipophilic environment, and the photosensitizer moiety can thus be inserted into the cell membrane. The efficacy of the carriers for photochemical internalization (PCI) mediated gene delivery was evaluated in vitro using the HCT116/LUC human colon carcinoma cell line. The efficacy of transfection was comparable to what could be achieved by the reference compound and current clinical candidate TPCS_2a

In vitro bioactivity of different degree of deacetylation chitosan, a potential coating material for titanium implants.

To access publisher's full text version of this article. Please click on the hyperlink in Additional Links field.Clinical treatment of orthopaedic tissue injuries often involves the use of titanium and titanium alloys with considerable research focusing on the surface modification of these materials. Chitosan, the partly deacetylated form of chitin, is one of the materials under investigation as surface coating for orthopaedic implants in order to improve osteo-integration and cellular attachment. In this study, we determined the effects of the degree of deacetylation (DD) of chitosan membranes on attachment, proliferation and osteogenic differentiation of MC3T3-E1 mouse preosteoblasts. Chitosan membranes were coated with fibronectin to promote biocompatibility and cellular attachment. Membranes were characterized in terms of wettability and surface topography using water contact angle measurements and atomic force microscopy. The results in this study indicate that the surface roughness and fibronectin adsorption increase with increased DD. A higher DD also facilitates attachment and proliferation of cells, but no induction of spontaneous osteogenic differentiation was observed. Lower DD chitosan membranes were successfully prepared to sustain attachment and were modified by crosslinking with glutaraldehyde to promote long-term studies. The chitosan membranes used in this study are suitable as a potential coating for titanium implants.Icelandic Research Fund 090007023 Icelandic Technology Development Fund 06136200

Unprecedented “In Water” Imidazole Carbonylation: Paradigm Shift for Preparation of Urea and Carbamate

The first “In Water” imidazolecarbonylation of amine is described. A one pot reaction of carbonylimidazolide in water with a nucleophile provides an efficient and general method for the preparation of urea, carbamates and thiocarbamates. Use of an anhydrous solvent and an inert atmosphere could be avoided. Product precipitate out from the reaction mixture and can be obtained in high purity by filtration, resulting in a simple and scalable method