4.1 General experimental procedures

The equipment employed for acquiring HRESIMS, NMR, UV–Vis, IR, ECD, and ORD data, as well as the HPLC systems utilized for both analysis and separation, are consistent with those detailed in previous studies [14, 20]. UV–Vis, ECD, and ORD were measured in the solutions of MeOH. For semi-preparative HPLC separations, either ODS-A columns (YMC, 5 μm, 1 × 25 cm, 4 mL/min) or πNAP columns (COSMOSIL, 5 μm, 1 × 25 cm, 4 mL/min) were deployed.

4.2 Strain material, fermentation and isolation

Strain GZWMJZ-662 was obtain from the roots of H. cordata, [14] and was determined as Streptomyces species (16S rRNA, GenBank No. OR083423). The strain was grown on ISP2 liquid cultured medium in 500 mL Erlenmeyer flasks for 3 days (28 °C and 180 rpm) to yield seed liquid. Two hundreds of sterile cultural bags each containing 50 g rice, 10 g soybean powder, 0.25 g sodium chloride and 50 mL water were static culture for one month after seed liquid (9 mL) was added. The culture media were extracted with ethyl acetate (EtOAc) and methanol (MeOH) (10:1, v/v). After evaporated, the residual was redispersed into MeOH (5 L) and washed petroleum ether (PE) (5 L*3 times). Then, the methanol was evaporated to yield duck extract (270 g).

The extract was loaded to a normal-phase silica gel column, and eluted by PE, DCM, and DCM:MeOH (100:1 to 1:1, v/v). After thin-layer chromatography detection and sample combination, 37 fractions (Fr1 − Fr37) were obtained.

Fr.20 (8.9 g) was separated by Sephadex LH-20 (MeOH:DCM = 1:1, v/v)) into Fr.20.1 to Fr.20.10. Fr.20.5 (510 mg) was initially separated by PTLC using EtOAc, yielding Fr.20.5.1 to Fr.20.5.3. Fr.20.5.1 (115 mg) was further separated using HPLC (ODS-A column) to obtain 11 (tR = 25.5 min, 8.8 mg) using 60% MeOH-H2O containing 0.05% TFA. Fr.20.5.2 (64 mg) was separated by an intelligent flash purification system (C18 column) using a gradient elution of 5% to 100% MeOH-H2O (containing 0.1% TFA) to obtain 4 (10.1 mg). Fr.20.5.3 (39 mg) was separated by HPLC using ODS-A column to obtain 1 (tR = 66 min, 2.1 mg) using 65% MeOH-H2O (containing 0.05% TFA) at 10 mL/min. Fr.20.4 (741 mg) was separated by a flash purification system (C18 column) using a gradient elution of 5% to 100% MeOH-H2O (0.1% TFA) to obtain 8 fractions Fr.20.4.1 to Fr.20.4.8). Fr.20.4.8 (27 mg) was separated by HPLC (ODS-A column) to obtain 2 (tR = 20.3 min, 2.2 mg) using 60% MeOH-H2O (0.05% TFA).

Fr.25 (7.5 g) was separated by Sephadex LH-20 into 9 fractions (Fr.25.1 − Fr.25.9) using MeOH and DCM (1:1, v/v). Fr.25.7 (564 mg) was separated by a C18 flash chromatography column using a gradient elution of 5% to 100% MeOH-H2O (0.1% TFA) to obtain 8 subfractions (Fr.25.7.1 − Fr.25.7.8). Fr.25.7.1 (41 mg) was washed with MeOH and DCM separately, resulting in a white insoluble substance 9 (7.8 mg). Fr.25.7.6 (49 mg) was separated by a semi-preparative πNAP column to obtain 10 (tR = 18.0 min, 5.5 mg) using 80% MeOH-H2O (containing 0.05% TFA). Fr.25.7.4 (44 mg) was separated by a semi-preparative πNAP column to obtain 7 (tR = 25.5 min, 3.5 mg) using 65% MeOH-H2O (0.05% TFA).

Fr.28 (4.714 g) was separated by Sephadex LH-20 into 9 fractions (Fr.28.1 − Fr.28.9) using MeOH and DCM (1:1, v/v) as the eluent. Fr.28.6 (226.7 mg) was further separated by Toyopearl HW-40F resin into 2 fractions (Fr.28.6.1 and Fr.28.6.2) using methanol as the eluent. Fr.28.6.1 (93 mg) was separated by an ODS-A chromatography column to obtain 8 (tR = 14.3 min, 8.7 mg) using 75% MeOH-H2O (containing 0.05% TFA). Similarly, Fr.28.6.2 (103 mg) was separated by a semi-preparative ODS-A chromatography column to obtain 5 (tR = 18 min, 20.9 mg) using 55% MeOH-H2O (0.05% TFA).

Fr.30 (8.791 g) was separated by Sephadex LH-20 into 9 fractions (Fr.30.1 − Fr.30.9) using equal volume of MeOH and DCM as eluent. Fr.30.6 (1.9 g) was further subjected to a C18 flash chromatography column (5% to 100% MeOH-H2O, containing 0.1% TFA) to obtain 15 fractions (Fr.30.6.1 − Fr.30.6.15). Fr.30.6.4 (98 mg) was then purified by semi-preparative HPLC (ODS-A) to obtain 6 (tR = 12.0 min, 5.1 mg) using 50% MeOH-H2O (containing 0.05% TFA).

Fr.31 (2.7 g) was separated by Toyopearl HW-40F gel resin into 11 fractions (Fr.31.1 − Fr.31.11) using equal volume of MeOH and DCM the eluent. Fr.31.4 (408 mg) underwent initial separation by a Flash chromatography column (C18) using a gradient elution of 5% to 100% MeOH-H2O (containing 0.1% TFA) to obtain 4 fractions (Fr.31.4.1 − Fr.31.4.4). Fr.31.4.1 (120 mg) was further purified by a semi-preparative ODS-A chromatography column to obtain 3 (tR = 12.4 min, 28.4 mg) using 65% MeOH-H2O (containing 0.05% TFA).

4.3 Spectroscopic data of compounds4.3.1 Dibohemamine I (1)

White powder; \([\alpha]_\text^\) =  − 79.0 (c 0.1); UV–Vis λmax(logε) 248 (4.45), 285 (4.18), 346 (4.11) nm; IR (KBr) νmax: 3272, 3151, 2979, 2930, 1712, 1692, 1646, 1554, 1451, 1217, 1132, 1073, 1013, 925, 845, 800, 724, 664, 582 cm−1; ECD (0.87 mM) λmax (Δε) 246 (+ 22.6), 285 (− 61.1), 345 (+ 15.9) nm; chemical shifts of 1H and 13C (Table 1); HR-ESIMS m/z 597.2433 [M + Na]+ (calcd for C29H39O6N4ClNa 597.24503).

4.3.2 Dibohemamine J (2)

White powder; \([\alpha]_\text^\) =  − 167.0 (c 0.1); UV–Vis λmax (log ε) 247 (4.16), 288 (3.84), 344 (3.81) nm; IR (KBr) νmax: 3273, 2979, 2933, 1682, 1646, 1567, 1495, 1446, 1383, 1206, 1183, 1133, 1064, 1011, 842, 801, 722, 664, 587, 544 cm−1; ECD (0.76 mM) λmax (Δε) 248 (+ 15.0), 288 (− 54.8), 345 (+ 15.5) nm; chemical shifts of 1H and 13C (Table 1); HR-ESIMS m/z 662.3174 [M + H]+ (calcd for C35H44O8N5, 662.31844).

4.3.3 Dibohemamine K (3)

White powder; \([\alpha]_\text^\) =  − 78.0 (c 0.1); UV–Vis λmax (log ε) λmax(logε) 249 (4.50), 284 (4.23), 346 (4.20) nm; IR (KBr) νmax: 3275, 3217, 2980, 2934, 1712, 1692, 1643, 1554, 1449, 1375, 1331, 1214, 1183, 1135, 1074, 1017, 926, 898, 843, 801, 760, 724, 661, 587 cm−1; ECD (0.22 mM) λmax (Δε) 248 (+ 28.7), 285 (− 71.2), 343 (+ 18.7) nm; chemical shifts of 1H and 13C (Table 1); HR-ESIMS m/z 557.2946 [M + H]+ (calcd for C29H41O7N4, 557.29698).

4.3.4 Dibohemamine L (4)

White powder; \([\alpha]_\text^\) =  − 110.0 (c 0.1); UV–Vis λmax(logε) 246 (4.51), 285 (4.22), 347 (4.19) nm; IR (KBr) νmax: 3210, 3031, 2977, 2916, 1708, 1646, 1567, 1492, 1455, 1370, 1324, 1214, 1123, 1053, 1015, 902, 843, 700.1, 674, 587, 530 cm−1; ECD (0.45 mM) λmax (Δε) 245 (+ 34.0), 285 (− 92.8), 347 (+ 30.2) nm; chemical shifts of 1H and 13C (Table 2); HR-ESIMS m/z 575.2468 [M + Na]+ (calcd for C29H36O7N4Na, 575.24762).

4.3.5 Dibohemamine M (5)

White powder; \([\alpha]_\text^\) =  − 87.0 (c 0.1); UV–Vis λmax(logε) 247 (4.47), 285 (4.20), 346 (4.19) nm; IR (KBr) νmax: 3273, 3148, 2980, 2936, 1708, 1683, 1647, 1554, 1452, 1372, 1324, 1211, 1185, 1135, 1074, 1015, 929, 906, 843, 801, 724, 662, 590 cm−1; ECD (0.23 mM) λmax (Δε) 245 (+ 21.6), 286 (− 56.4), 346 (+ 16.5) nm; chemical shifts of 1H and 13C (Table 2); HR-ESIMS m/z 555.2809 [M + H]+ (calcd for C29H39O7N4,555.28133).

4.3.6 Dibohemamine N (6)

White powder; \([\alpha]_\text^\) =  − 113.3 (c 0.1); UV–Vis λmax(logε) 249 (4.50), 284 (4.23), 346 (4.20) nm; IR (KBr) νmax: 3273, 3210, 2982, 2933, 2834, 1712, 1693, 1674, 1550, 1492, 1455, 1399, 1372, 1326, 1214, 1176, 1123, 1079, 1054, 1017, 977, 928, 902, 845, 774, 699, 668, 586 cm−1; ECD (0.22 mM) λmax (Δε) 244 (+ 32.9), 285 (− 68.6), 346 (+ 28.4) nm; chemical shifts of 1H and 13C (Table 2); HR-ESIMS m/z 571.2740 [M + H]+ (calcd for C29H39O8N4, 571.27624).

4.3.7 Dibohemamine O (7)

White powder; \([\alpha]_\text^\) =  − 175.3 (c 0.1); UV–Vis λmax(logε) 248 (4.46), 285 (4.17), 347 (4.13) nm; IR (KBr) νmax: 3273, 3210, 2982, 2939, 1683, 1647, 1545, 1512, 1446, 1377, 1326, 1208, 1135, 1067, 1011, 929, 905, 843, 801, 724, 668, 579, 536 cm−1; ECD (0.90 mM) λmax (Δε) 244 (+ 27.4), 284 (− 66.4), 348 (+ 29.2) nm; chemical shifts of 1H and 13C (Table 2); HR-ESIMS m/z 555.2791 [M + H]+ (calcd for C29H39O7N4, 555.28133).

4.4 Cytotoxicity assay

The cytotoxic activity of 1–11 against eighteen cell lines were assayed as our described previously [14, 20]. The tested cell lines see Table S3.