Sorokiniol: a new enzymes inhibitory metabolite from fungal endophyte Bipolaris sorokiniana LK12

Identification of the metabolites

The isolated metabolites were characterized by spectroscopic data (UV, IR, ¹H-NMR, ¹³C-NMR, 2D NMR, ESI and MS/MS studies). Compound 1 was characterized as a new constituent, whereas compound 2 and 3 were identified as earlier reported BZR-cotoxin I and BZR-cotoxin IV respectively. HR-EI-MS data showed that the molecular weight of chemical compound 1 was 374.3543 (calcd. for C₂₆H₄₆O 374.3549), whereas ESI-MS indicated the molecular weight of compound 2 as 968.6287 [M?+?H]⁺ (calcd. for C₄₈H₈₆N₇O₁₃, 968.6283) and compound 3 as 876.5239 [M?+?H]⁺ (calcd. for C₄₇H₇₀N₇O₉, 876.5244).

Compound 1: Pale yellow gummy solid (24.5 mg); m.p. 170–175 ° C, [?]
_D³⁰ +0.8° (CHCl₃; c 0.0013,); IR ?_max (CHCl₃) 3400 (OH); 2922, 1591, and 1463 (aromatic functionalities); ¹H-NMR (600 MHz, CDCl₃): ? 7.21 (2H, d, J?=?8.4 Hz), 6.94 (2H, d, J?=?8.4 Hz), 3.67 (2H, m), 2.83 (1H, m), 2.27 (2H, m), 1.53-1.21 (16H, overlap signal), 1.29 (14H, s), 1.23 (6H, d, J?=?6.1 Hz); ¹³C-NMR (150 MHz, CDCl₃): ? 148.7 (C-1), 139.2 (C-4), 126.9 (C-2, C-6), 117.2 (C-3, C-5), 56.9 (C-20?), 36.9 (C-4?), 32.4 (C-5?), 31.9 (C-1?), 30.9 (C-19?), 29.2 (C-6? to C-18?), 22.7 (C-2?, C-3?); EI-MS (m/z): 374 [M]⁺, 119 [M – side chain alcohol]⁺; HR-EI-MS (m/z): 374.3543 (calcd. for C₂₆H₄₆O 374.3549).

Compound 2: Colorless amorphous powder (4.9 mg); IR ?_max (CHCl₃) 3430 (OH); 2950, 2890, 1755, 1670, and 1645; ¹H-NMR (600 MHz, CDCl₃): ? 8.11 (1H, d, J?=?8.2 Hz, NH), 7.28 (1H, br s, NH), 5.52 (1H, d, J?=?10.1 Hz), 5.43 (1H, d, J?=?6.7 Hz), 5.14 (1H, d, J?=?10.7 Hz), 5.06 (1H, d, J?=?10.4 Hz), 5.02 (1H, d, J?=?8.5 Hz), 4.86 (2H, m), 4.71 (1H, m), 4.64 (1H, m), 4.23 (1H, br s), 3.80 (1H, br s), 3.57 (1H, dd, J?=?9.8, 5.8 Hz), 3.27 (3H, s), 3.12 (3H, s), 2.93 (3H, s), 2.85 (3H, s), 1.39 (3H, d, J?=?6.7 Hz), 1.25 (3H, d, J?=?6.4 Hz), 2.45-1.20 (11H, m), 1.07 (3H, d, J?=?6.7 Hz), 1.20-0.86 (28H, m), 0.81 (3H, d, J?=?6.4 Hz), 0.73 (3H, d, J?=?6.7 Hz); HR-ESI-MS (m/z): 968.6287 [M?+?H]⁺ (calcd. for C₄₈H₈₆N₇O₁₃, 968.6283).

Compound 3: Amorphous powder (5.3 mg); IR ?_max (CHCl₃) 3430, 2975, 2880, 1730, 1680, 1525; ¹H-NMR (600 MHz, CDCl₃): ? 7.54 (1H, br s, NH), 7.38 (1H, d, J?=?7.3Hz, NH), 7.35-7.17 (11H, m), 7.06 (1H, d, J?=?5.6 Hz, NH), 7.00 (1H, br s, NH), 6.69 (1H, d, J?=?8.9 Hz, NH), 4.85 (1H, d, J?=?5.8 Hz), 4.72 (1H, m), 4.54 (1H, t, J?=?7.8 Hz), 4.34 (1H, dd, J?=?7.0, 7.3 Hz), 4.05-3.85 (2H, m), 3.78 (1H, dd, J?=?4.3, 16.3 Hz), 3.68 (1H, m), 3.49-3.30 (3H, m), 3.24-3.07 (2H, m), 3.02 (3H, s), 2.20-1.10 (10H, m), 1.03 (3H, d, J?=?7.0 Hz), 0.99 (3H, d, J?=?6.7 Hz), 0.90-0.85 (12H, m), 0.79 (3H, t, J?=?7.3 Hz); HR-ESI-MS (m/z): 876.5239 [M?+?H]⁺ (calcd. for C₄₇H₇₀N₇O₉, 876.5244).