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A new synthesis method was developed and optimized by a full factorial design for conjugating hydroxycinnamic acids (HCA-s) to chitosan. Cinnamic acid and tert-butyldimethylsilyl protected HCA-s were converted to their corresponding acyl chlorides and reacted with 3,6-di-O-tert-butyldimethylsilyl-chitosan to selectively form amide linkages, resulting in water-soluble conjugates after deprotection. Nineteen conjugates were obtained with various degrees of substitution (DS) ranging from 3% to 60%. The conjugates were found to be bactericidal against Staphylococcus aureus and Escherichia coli, with their activities equal to chitosan at low DS but an increase in the DS correlated with reduced activity. DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging assay was performed to determine the EC50 values. Chitosan only exhibited low antioxidant activity, whereas the HCAchitosan conjugates exhibited higher antioxidant activities correlating with the DS. One caffeic acid conjugate (21%) was 4000 times more active than chitosan and more active than free caffeic acid., The research work was funded by the Icelandic Research Fund (Rannis Grant No. 185188-053) and by a doctoral grant from the University of Iceland research fund., Pre-print (óritrýnt handrit)

Here we describe the first synthesis of a new type of polysaccharides derived from chitosan. In these structures, the 2-amino group on the pyranose ring was quantitively replaced by an aromatic 1,2,3-triazole moiety. The 2-amino group of chitosan and di-TBDMS chitosan was converted into an azide by diazo transfer reaction. The chitosan azide and TBDMS-chitosan azide were poorly soluble but could be fully converted to triazoles by “copper-catalysed Huisgen cycloaddition” in DMF or DMSO. The reaction could be done with different alkynes but derivatives lacking cationic or anionic groups were poorly soluble or insoluble in tested aqueous and organic solvents. Derivatives with N,N-dimethylaminomethyl, N,N,N-trimethylammoniummethyl, sulfonmethyl, and phosphomethyl groups linked to the 4-position of the triazole moiety were soluble in water at neutral or basic conditions and could be analyzed by 1H, 13C APT, COSY, and HSQC NMR. The quaternized cationic chitotriazolan's had high activity against S. aureus and E. coli, whereas the anionic chitotriazolan's lacked activity.

Publisher's version (útgefin grein), N,N,N-trimethyl chitosan (TMC) with 93% degree of trimethylation was synthesized. TMC and the chitosan starting material were subjected to acidic hydrolysis to produce 49 different samples with a reduced average molecular weight (Mw) ranging from 2 to 144 kDa. This was done to allow the investigation of the relationship between antibacterial activity and Mw over a wide Mw range. NMR investigation showed that hydrolysis did not affect the degree of trimethylation (DSTRI) or the structure of the polymer backbone. The activity of TMC against Staphylococcus aureus (S. aureus) increased sharply with Mw until a certain Mw value (critical Mw for high activity, CMW) was reached. After the CMW, the activity was not affected by a further increase in the Mw. A similar pattern of activity was observed for chitosan. The CMW was determined to be 20 kDa for TMC and 50 kDa for chitosan., This study was initially funded by the Icelandic Research Fund (Grant No. 120443021) and by the EEA Scholarship and Training Fund. The final work was funded by the Icelandic Technical Development fund through the Marine Biotech ERA-NET Project—Blueteeth (Grant No. 179012-0612).

A new synthetic approach employing two types of protecting groups, tertiarybutyldimethylsilyl (TBDMS) and tertiarybutyloxycarbonyl (Boc) was developed to obtain a series of guanidinylated chitosan derivatives. The synthesis was carried out in organic solvents which allowed quantitative reaction, a good control on the degree of substitution, and 100% substitution of the chitosan amino groups. Similar derivatives carrying the trimethylammonium group were also synthesized as reference compounds. All the derivatives were characterized using 1 H and COSY NMR and IR spectroscopy. The antibacterial effect against clinically relevant strains of S. aureus and E. coli was found to increase with increase in the degree of substitution and decrease in the spacer length of the derivatives in both the series. An optimum activity could be obtained at a degree of substitution above 0.5 for most derivatives. The trimethylammonium derivatives showed slightly higher activity than the corresponding guanidinium derivatives but a similar structure–activity relationship was obtained.

A highly efficient method for chemical modification of chitosan biopolymers by reductive amination to yield N,N-dialkyl chitosan derivatives was developed. The use of 3,6-O-di-tert-butyldimethylsilylchitosan as a precursor enabled the first 100% disubstitution of the amino groups with long alkyl chains. The corresponding mono N-alkyl derivatives were also synthesized, and all the alkyl compounds were then quaternized using an optimized procedure. These well-defined derivatives were studied for antibacterial activity against Gram positive S. aureus, E. faecalis, and Gram negative E. coli, P. aeruginosa, which could be correlated to the length of the alkyl chain, but the order was dependent on the bacterial strain. Toxicity against human red blood cells and human epithelial Caco-2 cells was found to be proportional to the length of the alkyl chain. The most active chitosan derivatives were found to be more selective for killing bacteria than the quaternary ammonium disinfectants cetylpyridinium chloride and benzalkonium chloride, as well as the antimicrobial peptides melittin and LL-37.

Here we report that grafting of a short antimicrobial peptide, anoplin, to chitosan polymers is a strategy for abolishing the hemolytic propensity, and at the same time increasing the activity of the parent peptide. Anoplin-chitosan conjugates were synthesized by CuAAC reaction of multiple peptides through 2-azidoacetyl groups on chitosan.

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.

Quaternary N -(2-( N , N , N -tri-alkyl ammoniumyl and 2-pyridiniumyl) acetyl) derivatives of chitosan polymer, chitooligomer, and glucosamine (monomer) were synthesized for the purpose of investigating the structure activity relationship (SAR) for the antibacterial effect. Novel methods were used in the synthesis. The final chitosan and chitooligomer derivatives could thus be obtained in two steps without prior protection of the hydroxyl groups. However, in order to obtain chitosan derivatives with the bulky N , N -dimethyl- N -dodecyl- and N , N -dimethyl- N -butyl side chains three steps were needed, starting from 3,6- O -di- tert -butyldimethylsilyl chitosan (3,6- O -di-TBDMS chitosan) as the key intermediate. The quaternary ammoniumyl acetyl derivatives of glucosamine were synthesized from glucosamine or tetra- O -acetylglucosamine. N , N , N -trimethyl chitosan (TMC) was used as reference compound for investigation of antibacterial activity. Clinical Laboratory Standard Institute (CLSI) protocols were used to determine MIC and MLC for activity against clinically important Gram-positive strains Staphylococcus aureus (ATCC 25923), and S. aureus (MRSA) (ATCC 43300), and Gram-negative strains of Escherichia coli (ATCC 25922), P. aeriginosa (ATCC 27853) and Enterococcus facialis (ATCC 29212). The MIC values for the compounds ranged from 8 to ⩾8192 mg/L. In general the N -(2-( N , N -dimethyl- N -dodecyl ammoniumyl) acetyl) derivatives of chitooligomer and glucosamine monomer were more active against bacteria than derivatives with shorter alkyl chains. In contrast the N -(2-( N , N -dimethyl- N -dodecyl ammoniumyl) acetyl) derivatives of chitosan were less active than derivatives with N -(2- N , N , N -trimetylammoniumyl) acetyl or N -(2-( N -pyridiniumyl) acetyl) quaternary moiety. N , N , N -trimethyl chitosan (TMC) was the most active compound in this study.

Well characterized methylpiperazine, mono-quaternary dimethylpiperazine and di-quaternary trimethylpiperazine derivatives of chitosan, with different degrees of substitution, were investigated for antibacterial activity against five strains of Gram-positive and Gram-negative bacteria. Some of the methylpiperazine and the dimethyl piperazine derivatives of chitosan, with low degree of substitution, were active against bacteria at pH 5.5 with minimum inhibitory concentration (MIC) ⩾64 μg/ml. Chitosan derivatives with the di-quaternary substituents were active against bacteria with MIC as low as 8 μg/ml and in general more active at pH 7.2 than at pH 5.5. The minimum lethal concentrations (MLC) were the same as the MIC within 1–2 dilutions. The most active compound induced gradual decrease in the count of viable bacteria over 8 h at 8× MIC. The results are consistent with the interpretation that methylpiperazine and mono-quaternary dimethylpiperazine substituents do not contribute to activity against bacteria, whereas di-quaternary trimethylpiperazine moiety, will contribute to antibacterial activity.

The purpose of this study was to synthesize series of methylated chitosaccharide derivatives, possessing various degree of methylation, and to determine their structure activity relationship (SAR) with regard to their antibacterial effect against Staphylococcus aureus. Chitosan polymer and chitooligomers were used as starting materials and were methylated by reaction with methyl iodide. Depending on the reaction conditions the degree of N-quaternization ranged from 0% to 74%, with varying degree of N,N-dimethylation, N-monomethylation and O-methylation. More selective N-quaternization could be obtained with protection group strategy. At pH 5.5 the chitosaccharide polymers and their methylated derivatives were active against S. aureus with minimal inhibitory concentration (MIC) ranging from 16 to 512 μg/mL. At pH 7.2 the non-quaternized derivatives were inactive but their highly N-quaternized derivatives showed MIC as low as 8 μg/mL. The chitooligomers, as well as their derivatives, were inactive at both pH’s. The SAR studies revealed that N-quaternization was mainly responsible for the antibacterial effects at pH 7.2, whereas it did not contribute to the antibacterial activity under acidic conditions.

The effect of degree of substitution on the antimicrobial activity of water-soluble quaternary chitosan N-betainates was determined against Escherichia coli and Staphylococcus aureus. Chitosan N-betainates showed low antimicrobial activity in neutral conditions and the glucosamine N-betainate prepared as a reference compound showed low activity also in acidic conditions. However, the antimicrobial activity increased with decreasing degrees of substitution in acidic conditions (pH 5.5), which suggests that for efficient antimicrobial action, the positive charge should be situated in the amino group of chitosan, rather than in the quaternary substituent.

A series of soft quaternary ammonium antimicrobial agents, which are analogues to currently used quaternary ammonium preservatives such as cetyl pyridinium chloride and benzalkonium chloride, were synthesized. These soft analogues consist of long alkyl chain connected to a polar headgroup via chemically labile spacer group. They are characterized by facile nonenzymatic and enzymatic degradation to form their original nontoxic building blocks. However, their chemical stability has to be adequate in order for them to have antimicrobial effects. Stability studies and antibacterial and antiviral activity measurements revealed relationship between activity, lipophilicity, and stability. Their minimum inhibitory concentration (MIC) was as low as 1 microg/mL, and their viral reduction was in some cases greater than 6.7 log. The structure-activity studies demonstrate that the bioactive compounds (i.e., MIC for Gram-positive bacteria of