*2.3. Identification of the Major Product*

To resolve the chemical structure of the product, the biotransformation was scaled up to 100 mL, with 1 mg/mL of 8-OHDe, 125 μg/mL of DgAS, and 300 mM of sucrose at pH 7 and 40 ◦C for 30-min incubation. About 90 mg of the product in the 100-mL reaction was purified with preparative high-performance liquid chromatography (HPLC). Based on the value of the optimal conversion (89.3%) (Figure 3), the maximum production yield of compound (**1**) from 100 mg of 8-OHDe is 142.3 mg (160 mg × 0.89); thus, the purification recovery yield is 62.5% (90/142). The chemical structure of the purified compound (**1**) was resolved with mass and nuclear magnetic resonance (NMR) spectral analysis. The mass analysis of the compound showed an [M + H]<sup>+</sup> ion peak at *m*/*z*: 433.18 in the electrospray ionization mass (ESI-MS) spectrum corresponding to the molecular formula C21H20O10. Then 1H and

13C nmR spectra, including distortionless enhancement by polarization transfer (DEPT), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC), correlation spectroscopy (COSY), and nuclear Overhauser effect spectroscopy (NOESY) spectra, were obtained, and the 1H and 13C nmR signal assignments were conducted accordingly (shown in Figures S1–S7). In addition to the signals of 8-OHDe, seven proton signals (from 3.22 to 5.48 ppm) and six carbon signals (from 60–100 ppm) indicated a glucose moiety. The J coupling constant (3.6 Hz) of the anomeric proton (5.48 ppm) in the 1H nmR spectra of compound (1) indicated the α-configuration for the glucopyranosyl moiety. The cross peak of H-1 with C-7 (5.48/148.8 ppm) in the HMBC spectrum, as well as the cross peak of H-1 with H-6 (5.48/7.38 ppm) in the NOESY spectrum, demonstrated the structure of compound (**1**) was 8-OHDe-7-*O*-α-glucoside. The key HMBC and NOESY correlations of compound (**1**) are shown in Figure S8, and the spectroscopic data is listed in Table S1. The downfield shift of the 1H signal H-1, the anomeric proton, of compound (**1**) compared to that of 8-OHDe-7-*O*-β-glucoside [20], indicated their different microenvironments. Figure 4 illustrates the biotransformation process of 8-OHDe by DgAS.

**Figure 4.** Biotransformation process of 8-OHDe by DgAS.
