## 1 Introduction  
Natural polymers to be used in different applications must often undergo chemical transformations. Among these transformations, oxidation presents a convenient approach to the alteration of the polysaccharide backbone by introduction of new functionalities, such as aldehyde or carboxyl groups, due to its relative simplicity and selectivity. Since the pioneering work of [PERSON] and [PERSON] [1], many oxidation protocols have been reported [2; 3]. In recent years, the introduction of the TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) radical as mediator in this kind of transformation has led to a tremendous boost in polysaccharide oxidation research. However, few existing reports take into account the depolymerization side reactions which are likely to occur during longer exposure of reactants and oxidized products to the reaction medium [2; 3]. As an alternative, \(N\)-hydroxphthalimide (NHPI) has been proposed to replace the TEMPO catalyst in many oxidation processes [4; 5; 6], including in the oxidation of cellulose. In the oxidation processes of cellulose, NHPI would react with a occatalyst in order to produce phthalimide-\(N\)-oxyl radical (PINO), which would initiate the reaction cycle [7]. Several procedures to generate PINO radical from NHPI have been reported, e.g., electrocatalytic, biocatalytic, and chemocatalytic systems [6]. In 2009, [PERSON] et al. reported that cellulose could be oxidized inthe presence of NHPI and various metallic or nonmetallic occatalysts at room temperature and in the presence of sodium hypochlorite and sodium bromide [8]. Other nonpersistent nitroxyl radicals have subsequently been proven to effectively oxidize the viscose fibers at room temperature and alkaline pH [9; 10]. Pullulan is a biodegradable polysaccharide produced by the fungus _Aureobasidium pullulans_. It is composed of maltotriosyl repeating units linked via \(\alpha\)-1,6-glycosidic bonds (Figure 1) [11]. Pullulan exhibits good biocompatibility and enzymatic degradation, making it a promising material for a wide range of applications, including pharmaceutics, food, and cosmetics [12]. Chemical functionalization is a valuable method often employed to alter the properties of pullulan, as well as to enhance its applicability in various fields. Chemical modifications of pullulan such as oxidation [13], etherification [14], esterification [15], and hydrogenation [16] have been reported. The oxidation of pullulan to carboxypullulan is an important direction to functionalization of the hydroxyl groups in the maltotriose unit of pullulan. The introduction of carboxylic acid groups in the pullulan backbone provides anionic polymers, which are able to interact more effectively with other charged compounds. Thus, pullulan can be readily oxidized at primary hydroxyl groups to the carboxylic moiety using the free nitroxyl radical, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), and a primary oxidant such as sodium hypochlorite (NaOCI). In this process, the nitrosonium salt is the key species resulting from the conversion of the nitroxyl radical in the presence of NaBr/NaOCI [17]. The resulting oxidized pullulan has recently been found useful in applications for incorporation of magnetic nanoparticles used in magnetic resonance imaging [18], as well as in drug delivery, in preparation of uncoadhesive buccal films loaded with enalapril maleate [19]. According to the current trends in catalysis, attempts have been made to immobilize NHPI onto solid supports in order to obtain easily separable and reusable catalysts. For example, polymers [20], silica gel [21], and zeolite [22] were applied as solid supports. However, until now, these solid catalysts have been applied only for the aerobic oxidation of low molecular organic compounds, such as toluene, p-methoxytoluene [20; 21], and 1-phenylethanol [23].