Research Article: Regioselective Sequential Modification of Chitosan via Azide-Alkyne Click Reaction: Synthesis, Characterization, and Antimicrobial Activity of Chitosan Derivatives and Nanoparticles

Date Published: April 30, 2015

Publisher: Public Library of Science

Author(s): Atif Sarwar, Haliza Katas, Siti Noradila Samsudin, Noraziah Mohamad Zin, Daniel Rittschof.


Recently, the attention of researchers has been drawn toward the synthesis of chitosan derivatives and their nanoparticles with enhanced antimicrobial activities. In this study, chitosan derivatives with different azides and alkyne groups were synthesized using click chemistry, and these were further transformed into nanoparticles by using the ionotropic gelation method. A series of chitosan derivatives was successfully synthesized by regioselective modification of chitosan via an azide-alkyne click reaction. The amino moieties of chitosan were protected during derivatization by pthaloylation and subsequently unblocked at the end to restore their functionality. Nanoparticles of synthesized derivatives were fabricated by ionic gelation to form complexes of polyanionic penta-sodium tripolyphosphate (TPP) and cationic chitosan derivatives. Particle size analysis showed that nanoparticle size ranged from 181.03 ± 12.73 nm to 236.50 ± 14.32 nm and had narrow polydispersity index and positive surface charge. The derivatives and corresponding nanoparticles were evaluated in vitro for antibacterial and antifungal activities against three gram-positive and gram-negative bacteria and three fungal strains, respectively. The minimum inhibitory concentration (MIC) of all derivatives ranged from 31.3 to 250 µg/mL for bacteria and 188 to1500 µg/mL for fungi and was lower than that of native chitosan. The nanoparticles with MIC ranging from 1.56 to 25 µg/mLfor bacteria and 94 to 750 µg/mL for fungi exhibited higher activity than the chitosan derivatives. Chitosan O-(1-methylbenzene) triazolyl carbamate and chitosan O-(1-methyl phenyl sulfide) triazolyl carbamate were the most active against the tested bacterial and fungal strains. The hemolytic assay on erythrocytes and cell viability test on two different cell lines (Chinese hamster lung fibroblast cells V79 and Human hepatic cell line WRL68) demonstrated the safety; suggesting that these derivatives could be used in future medical applications. Chitosan derivatives with triazole functionality, synthesized by Huisgen 1,3-dipolar cycloaddition, and their nanoparticles showed significant enhancement in antibacterial and antifungal activities in comparison to those associated with native, non-altered chitosan.

Partial Text

Recently, there has been a remarkable surge in research to explore properties and pharmaceutical applications of chitosan, a positively charged polymer. Chitosan is known to possess numerous biological properties such as antibacterial [1,2], antifungal [3], anticancer [4], anticholesterolemic [5], wound healing properties [6], biocompatibility, and biodegradability [7]. In addition, chitosan has also been utilized as a mucoadhesive in the promotion of transmucosal absorption [8], a bioadhesive agent in nasal drug delivery and for other mucosal routes [9,10], as well as a delivery system for plasmid DNA (pDNA) [11], and genetic material [12].

Chitosan is a unique polymer associated with several biological activities and has attracted much attention recently for further development as an antimicrobial agent. The use of a natural product like chitosan for various pharmaceutical applications is highly recommended because of its environmental and ecologic benefits. In this study, a series of chitosan derivatives have been successfully synthesized by cycloaddition of azide-alkyne compounds. The present approach enables us to design highly chemoselective and biologically active chitosan triazolyl derivatives and formulate them into NPs. All derivatized chitosan triazolyl compounds and their corresponding nanoparticles exhibited better antibacterial and antifungal activities while preserving the non-toxicity of the unmodified chitosan. These findings prove that introduction of desired triazole rings by chemoselective modifications of chitosan, retaining the backbone structure of polymer, and maintaining its intrinsic properties could potentially be used as a powerful tool to design promising chitosan derivatives with well-defined and improved biological properties. Further investigations will be carried out to evaluate additional activities of these derivatives and their nanoparticles while designing and synthesizing more potent compounds in parallel.