Synthesis, Characterization, and Antifungal Activity of Pyridine-Based Triple Quaternized Chitosan Derivatives

Abstract

In this study, a series of triple quaternized chitosan derivatives, including 6-<i>O</i>-[(2-hydroxy-3-trimethylammonium)propyl]-2-<i>N</i>-(1-pyridylmethyl-2-ylmethyl)-<i>N</i>,<i>N</i>-dimethyl chitosan chloride (<b>7</b>), 6-<i>O</i>-[(2-hydroxy-3-trimethylammonium)propyl]-2-<i>N</i>-(1-pyridylmethyl-3-yl- methyl)-<i>N</i>,<i>N</i>-dimethyl chitosan chloride (<b>8</b>), and 6-<i>O</i>-[(2-hydroxy-3-trimethylammonium)propyl]- 2-<i>N</i>-(1-pyridylmethyl-4-ylmethyl)-<i>N</i>,<i>N</i>-dimethyl chitosan chloride (<b>9</b>) were successfully designed and synthesized via reacting epoxypropyl trimethylammonium chloride with the <i>N</i>-pyridinium double quaternized chitosan derivatives. Detailed structural characterization was carried out using FT-IR and ¹H-NMR spectroscopy, and elemental analysis. Besides, the activity of the triple quaternized chitosan derivatives against three common plant pathogenic fungi, <i>Watermelon fusarium</i>, <i>Fusarium oxysporum</i>, and <i>Phomopsis asparagi</i>, was investigated in vitro. The results indicated that the triple quaternized chitosan derivatives had enhanced antifungal activity when compared to double quaternized chitosan derivatives and chitosan, especially at 1.0 mg/mL, which confirmed the theory that the higher density of positive charge contributed to the antifungal activity. Moreover, <b>8</b> with an almost 99% inhibitory index showed the better antifungal activity against <i>Watermelon fusarium</i>. Moreover, the cytotoxicity of the products was also evaluated in vitro on 3T3-L1 cells and all the triple quaternized chitosan derivatives exhibited low cytotoxicity. These results suggested that triple quaternized chitosan derivatives may be used as good antifungal biomaterials.