*3.2. Fungal Materials*

The fungus used in this research was isolated from the fruit of the marine mangrove plant *Bruguiera* collected in 2014 in Hainan Dongzhai Harbor Mangrove Reserve by using the standard protocol. The strain was identified as *Mycosphaerella* sp. (compared to no. KX067865.1) upon the analysis of ITS sequence data of the rDNA gene. The ITS sequence data obtained from the fungal strain has been submitted to GenBank with accession no. MN194208. A voucher strain was deposited in our laboratory.

#### *3.3. Fermentation, Extraction and Isolation*

The fungus *Mycosphaerella* sp. SYSU-DZG01 was grown on solid cultured medium in 100 × 1000 mL Erlenmeyer flasks at room temperature for 30 days under static conditions, each containing 80 g rice and 120 mL 0.3% saline. After incubation, the former was extracted with methanol twice and concentrated to yield 10.9 g of crude extract under reduced pressure. The crude extract was subjected to LC-HRESIMS analysis (Figure S29). Then, the residue was eluted by using gradient elution with petroleum ether/EtOAc from 9:1 to 0:10 (*v*/*v*) on silica gel CC to ge<sup>t</sup> ten fractions (Fr.1–Fr.10). Fr.2 (630 mg) was further eluted by silica gel CC using CH2Cl2/MeOH (40:1) to obtain Fr.2.1–Fr.2.3. Fr.2.3 (301 mg) was purified by Sephadex LH-20 CC and eluted with MeOH to obtain compound **2** (3.5 mg), **6** (11.1 mg) and 1**0** (3.6 mg). Fr.4 (217 mg) was applied to silica gel CC by CH2Cl2/MeOH (20:1) to obtain Fr.4.1–Fr.4.7. Fr.4.1 (8.1 mg) was further purified by Sephadex LH-20 CC using MeOH to obtain compound **1** (2.3 mg), **3** (2.2 mg), **8** (20.8 mg) and **9** (2.7 mg). Fr.5 (817 mg) was eluted (by CH2Cl2/MeOH, 25:3) to obtain Fr.5.1–Fr.5.5. Fr.5.1 (13.3 mg), Fr.5.2 (27.7 mg) and Fr.5.4 (10.9 mg) was purified by Sephadex LH-20 CC using CH2Cl2/MeOH (1:1) to yield compound **4** (4.3 mg), **5** (2.0 mg), **7** (3.7 mg) and **11** (2.7 mg).

Asperchalasine I (**1**): White powder; [α]25D = +61.4 (*c* 0.1, MeOH); UV (MeOH) λmax (log ε): 206 (4.53) nm; IR (KBr) νmax (cm−1): 3369, 1691, 1440, 1384, 1201, 1120, 1053; HRESIMS *m*/*z* 562.2798 [M − H]− (calcd. for C33H40O7N: 562.2799); 1H and 13C NMR data: see Table 1.

Dibefurin B(**2**): Colorless crystal; m.p. 67.8–69.2 ◦C; [α]25D = +0.3 (*c* 0.1, MeOH); UV (MeOH) λmax (log ε): 237 (3.98) nm; IR (KBr) νmax (cm−1): 3448, 1747, 1664, 1645, 1238, 1037; HRESIMS *m*/*z* 331.1187 [M − H]− (calcd. for C18H19O6, 331.1187); 1H and 13C NMR data: see Table 2.

Compound **3**: Colorless crystal; m.p. 89.8–91.9 ◦C; [α]25D = −37.1 (*c* 0.1, MeOH); UV (MeOH) λmax (log ε) 204 (4.39), 269 (3.24) nm; IR (KBr) νmax (cm−1): 3261, 2887, 1601, 1471, 1297, 767, 706; HRESIMS *m*/*z* 179.0716 [M − H]− (calcd. for C10H12O3, 179.0714; 1H and 13C NMR data: see Table 2.

Compound **4**: Colorless crystal; m.p. 95.9–97.8 ◦C; [α]25D = +3.4 (*c* 0.1, MeOH); UV (MeOH) λmax (log ε) 241 (3.66), 305 (3.56) nm; IR (KBr) νmax (cm−1): 3375, 2962, 1711, 1641, 1261, 1150, 933; HRESIMS *m*/*z* 225.0407 [M − H]− (calcd. for C10H10O6, 225.0407; 1H and 13C NMR data: see Table 2.

#### *3.4. X-Ray Crystallographic Data*

Colorless crystals of compounds **2**–**4** were obtained from MeOH-CH2Cl2 at room temperature by slow volatilization, and examined on an Agilent Xcalibur Nova single crystal diffractometer with Cu Kα radiation.

The crystallographic data for compound **2** has been deposited in the Cambridge Crystallographic Data Centre (CCDC number: 18022803)

Crystal data of **2**: C18H20O6, *Mr* = 332.34, triclinic, *a* = 6.9740(4) Å, *b* = 7.9800(4) Å, *c* = 14.3659(6) Å, α = 101.148(4)◦, β = 99.209(4)◦, γ = 98.479(5)◦, *V* = 761.05(7)Å3; space group *P-1*, *Z* = 2, *Dc* = 1.450 g/cm3, μ = 0.908 mm<sup>−</sup><sup>1</sup> and *F*(000) = 352.0; Crystal dimensions: 0.40 × 0.30 × 0.02 mm3. Independent reflections: 4998 (*R*int = 0.0269). The final *R*1 was 0.0522, *wR*2 = 0.1447 [*l* > 2σ (*I*)]. The goodness of fit on *F*<sup>2</sup> was 1.048.

The crystallographic data for compound **3** has been deposited in the Cambridge Crystallographic Data Centre (CCDC number: 18121203)

Crystal data of **3**: C10H12O3, *Mr* = 180.07, monoclinic, *a* = 4.7697(1) Å, *b* = 11.1895(3) Å, *c* = 9.1541(3) Å, α = 90◦, β = 93.829(3)◦, γ = 90◦, *V* = 487.47(2) Å3; space group *P21*, flack 0.14(18), *Z* = 2, *Dc* = 1.350 g/cm3, μ = 0.872 mm<sup>−</sup><sup>1</sup> and *F*(000) = 212.0; Crystal dimensions: 0.40 × 0.10 × 0.05 mm3. Independent reflections: 7438 (*R*int = 0.0620). The final *R*1 was 0.0445, *wR*2 = 0.1258 [*l* > 2σ (*I*)]. The goodness of fit on *F*<sup>2</sup> was 1.046.

The crystallographic data for compound **4** has been deposited in the Cambridge Crystallographic Data Centre (CCDC number: 18120705)

Crystal data of **4**: C10H10O6, *Mr* = 226.04, orthorhombic, *a* = 15.9208(7) Å, *b* = 6.6849(3) Å, *c* = 18.5162(7) Å, α = 90◦, β = 90◦, γ = 90◦, *V* = 1970.66(14) Å3; space group *Pbca*, *Z* = 8, *Dc* = 1.525 g/cm3, μ = 1.108 mm<sup>−</sup><sup>1</sup> and *F*(000) = 944.0; Crystal dimensions: 0.25 × 0.03 × 0.03 mm3. Independent reflections: 3833 (*R*int = 0.0496). The final *R*1 was 0.0485, *wR*2 = 0.1328 [*l* > 2σ (*I*)]. The goodness of fit on *F*<sup>2</sup> was 1.050.

## *3.5. Biological Assays*

#### 3.5.1. Inhibitory Activity of α-Glucosidase

The α-glucosidase inhibitory activity was assayed according to the reported method [29]. The inhibitory activity of α-glucosidase was tested in the 96-well plated with 100 mm PBS (KH2PO4-K2HPO4, pH 7.0) buffer solution each. Compounds **1**–**11**, acarbose and 1-deoxynojirimycin (positive control) were dissolved in DMSO, the substrate (*p*-nitrophenyl glycoside, 5 mM) were dissolved in PBS buffer solution and enzyme solutions (2.0 units/mL) were prepared. The assay was conducted in a 100 μL reaction system containing 20 μL enzyme stock solution, 69 μL PBS buffers and 1 μL of DMSO or testing materials. After 10 min incubation at 37 ◦C, 10 μL of the substrate was added and incubated for 20 min at 37 ◦C. The Absorbance which measured by a BIO-RAD (iMark) microplate reader at 405 nm was used to calculate the inhibitory activity according to the equation:

$$\text{T}\,\text{m}\,\left(\%\right) = \left[\text{(B}-\text{S)}\right]\text{B}\,\text{J} \times 100\%\,\text{\textdegree}\,\tag{1}$$

η (%) is the percentage of inhibition; B is the assay medium with DMSO; S is the assay medium with compound. The results of IC50 values were calculated by the nonlinear regression analysis. Acarbose and 1-deoxynojirimycin were used as positive controls.

## 3.5.2. Antioxidant Activity

The DPPH· scavenging was assayed according to the reported method [30]. The DPPH radical scavenging test was performed in 96-well microplates. Testing materials (compounds **1**–**11**) were added to 150 μL (0.16 mmol/L) DPPH solution in MeOH at a range of 50 μL solutions of different concentrations (2, 25, 50 and 100 μM). After 30 min, absorbance at 517 nm was measured and the percentage of activity was calculated. Ascorbic acid was used as a positive control.
