3.1 General experimental procedures

These are provided in the Supporting Information.

3.2 Plant material

We collected the twigs and leaves of S. glandulosa var. cordifolia from Yuanjiang County, Yunnan Province in August 2023. The plant was then identified by G.-H. Tang.

3.3 Extraction and isolation

Twigs and leaves of S. glandulosa var. cordifolia (14.5 kg, dry weight) were powdered and extracted, under ambient conditions, thrice with 95% ethanol (3 × 75 L), generating a crude extract Weighing 1.2 kg. An aqueous suspension of the crude extract was subjected to liquid–liquid partition against petroleum ether (PE), followed by ethyl acetate (EtOAc), and then n-butanol (n-BuOH). Fractionation of the EtOAc extract (280.0 g) on D101 macroporous resin chromatographic column (CC), using MeOH/H₂O (3:1 → 1:0, v/v), yielded two fractions (Fr. I and Fr. II). Fr. I (86.2 g) was subjected to a silica gel column using CH₂Cl₂/MeOH (1:0 → 0:1, v/v), yielding eight subfractions (Fr. IA−Fr. IH). Among these, subfraction Fr. IB (10.0 g) was further subjected to silica gel chromatography using a PE/EtOAc gradient (8:1 → 0:1, v/v), affording nine fractions (Fr. IB1−Fr. IB9). Fr. IB8 (1.5 g) was further subjected to Sephadex LH-20 CC (MeOH), affording compounds 1 (20.5 mg, tR = 18.2 min), 2 (3.2 mg, tR = 19.3 min), and 3 (16.8 mg, tR = 15.6 min) followed by semi-preparative HPLC refinement (MeCN/H₂O, 48:52, v/v; 3.0 mL/min).

3.4 Spectroscopic data of the compounds3.4.1 Strophioglandin A (1)

Colorless crystal; \(_^\)−160 (c 0.1, MeCN); UV (MeCN) λmax (log ε) 253 (4.42), 333 (3.90) nm; ECD (c 7.40 × 10−4, MeCN) λmax (Δε) 232 (+ 1.70), 354 (−3.07) nm; IR (neat) νmax 2948, 2857, 1584, 1559, 1455, 1256, 1190, 1060, 1018, 890 cm−1; 1H and 13C NMR data, see Table 1; HRESIMS m/z 293.1518 [M + Na]+ (calcd. for C18H22O2Na+, 293.1512).

3.4.2 Strophioglandin B (2)

Yellowish oil; \(_^\)−103 (c 0.1, MeCN); UV (MeCN) λmax (log ε) 240 (4.16), 269 (4.31), 355 (3.89) nm; ECD (c 3.52 × 10−4, MeCN) λmax (Δε) 196 (+ 3.80), 255 (+ 3.67), 277 (−3.26), 350 (−2.78) nm; IR (neat) νmax 2960, 2925, 2853, 1683, 1585, 1456, 1261, 1187, 1055, 1007, 896 cm−1; 1H and 13C NMR data, see Table 1; HRESIMS m/z 307.1302 [M + Na]+ (calcd. for C18H20O3Na+, 307.1305).

3.4.3 Strophioglandin C (3)

Yellowish oil; \(_^\)−55 (c 0.1, MeCN); UV (MeCN) λmax (log ε) 251 (4.45), 330 (4.00) nm; ECD (c 3.05 × 10−4, MeCN) λmax (Δε) 256 (−11.97), 319 (+ 3.43) nm; IR (neat) νmax 2948, 1732, 1568, 1454, 1343, 1259, 1180, 1073, 1003, 894, 845 cm−1; 1H and 13C NMR data, see Table 1; HRESIMS m/z 329.1751 [M + H]+ (calcd. for C20H25O4+, 329.1747).

3.5 Crystallographic data for 1

C18H22O2 (M = 270.35 g/mol): orthorhombic, space group P 21 21 21 (no. 19), a = 6.19478(9) Å, b = 6.86349(9) Å, c = 34.2241(4) Å, α = 90°, β = 90°, γ = 90°, V = 1455.14(3) Å3, Z = 4, T = 100 K, μ (Cu Kα) = 0.616 mm−1, Dcalc = 1.234 g/cm−3, 14 428 reflections measured (5.164° ≤ 2θ ≤ 157.466°), 3052 unique (Rint = 0.0449, Rsigma = 0.0436), which were used in all calculations. The final R1 was 0.0436 (I > 2σ(I)) and wR2 was 0.1176 (all data). Flack parameter:−0.06(10). CCDC number: 2422939.

3.6 ECD calculations

These are provided in the Supporting Information for 2 and 3.

3.7 Cell culture

Cell culture was performed according to the established protocol [25].

3.8 Cytotoxicity assay

Raw264.7 cells (5 × 104 cells/well), prior to compounds treatment for 24 h, were allowed to adhere in 96-well plates. Following 24 h incubation at 37 °C, cell viability was assessed by using CCK-8 reagent (Dojindo, Japan) with 10 μL reagent added per well. Absorbance was finally recorded by means of a multifunction microplate reader at 450 nm.

3.9 Analysis of NO production

Following a 24-h incubation period after plating Raw264.7 macrophages (5 × 104 cells/well) in 96-well plates, compounds were added at increasing concentrations (5, 10, and 20 μM) and incubated, with or without LPS (1 μg/mL), for 24 h in media. NO concentration in the culture medium was quantified using a Griess reagent kit, following the manufacturer’s protocol. For the assay, 50 μL of Griess reagent was mixed with an equal volume of cell culture supernatant. With quercetin serving as the positive control, the absorbance at 540 nm, by means of a multifunction microplate reader, was measured.

3.10 qRT-PCR analysis

This was performed according to the established protocol [25].

3.11 Western blotting analysis

This was performed according to the established protocol [25].

3.12 Statistical analysis

Statistical analysis followed the approach of reference [25].