*3.7. Characterizations of Mangiferin Glucosides*

The low aqueous solubility of mangiferin restricts its usage as a pharmaceutical agent. However, the glycosylation of mangiferin may mitigate such a restriction. Only a few studies have reported different glycosylation agents for mangiferin. Wu et al. (2013) used β-fructofuranosidase (E.C. 3.2.1.26; GH 32 family) to glycosylate mangiferin into fructosylβ-(2→6)-mangiferin and found that its DPPH radical scavenging activity was similar to that of mangiferin [45]. Nguyen et al. (2020) used dextransucrase (E.C. 2.4.1.5; GH 70 family) from *Leuconostoc mesenteroides* to glycosylate mangiferin into glucosyl-α-(1→6)-mangiferin (**1**) [46]. They found that the aqueous solubility of glucosyl-*α*-(1→6)-mangiferin (**1**) was 2300-fold higher than that of mangiferin. In this study, the amount of purified glucosyl-*α*- (1→6)-mangiferin (**1**) was too low to repeat the solubility experiment. The solubility of the newly identified maltosyl-*α*-(1→6)-mangiferin (**2**) was determined. The results showed that the solubility of maltosyl-*α*-(1→6)-mangiferin (**2**) was 5500-fold higher than that of mangiferin (Table 1). Thus, maltosyl-*α*-(1→6)-mangiferin (**2**) possesses higher solubility than glucosyl-*α*-(1→6)-mangiferin (**1**). It has been reported that the more sugar moieties in the glycosylated compounds, the higher the aqueous solubility of the glycosylated compounds [29–37].

**Figure 8.** Biotransformation process of mangiferin by *Pg*MA.

**Table 1.** Aqueous solubility of mangiferin and maltosyl-*α*-(1→6)-mangiferin (**2**).


<sup>1</sup> The mean (*n* = 2) is shown, and the standard deviations are represented by error bars. <sup>2</sup> The folds of the aqueous solubilities of the mangiferin glucoside derivatives are expressed as relative to that of mangiferin normalized to 1.

Mangiferin exhibits a wide pharmacological profile, and its antioxidant property is well known from previous studies. Furthermore, it has been associated with the redox aromatic system of the xanthone nucleus [3–10,12]. Thus, the antioxidative activities of the two mangiferin glucosides were determined using DPPH free radical scavenging assay. The assay showed that the antioxidant activity levels of mangiferin and its two glucosides were all higher than those of ascorbic acid (Figure 9). In other words, the antioxidant activities of the two mangiferin glucosides are comparable with those of mangiferin. The *ortho*-dihydroxyl groups on the benzene ring of the mangiferin structure have been reported to play a key role in exerting its antioxidant activity [1,2]. Both mangiferin glucosides remained the key functional groups after glycosylation; therefore, most of the antioxidant activity remained in the mangiferin derivatives. These glycoside derivatives (glucoside and fructoside) might possess different pharmacological properties. A futher study will focus on the bioactivities and bioavailability of these mangiferin derivatives

**Figure 9.** The 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity of mangiferin, mangiferin glucosides, and ascorbic acid. The DPPH scavenging activity was determined as described in Section 2. The IC50 values represent the concentrations required for 50% DPPH free radical scavenging activity. The mean (*n* = 3) is shown, and the standard deviations are represented by error bars. M1 and M2 are glucosyl-*α*-(1→6)-mangiferin and maltosyl-*α*-(1→6)-mangiferin, respectively.
