8′-epimer of herbicidin F and its congeners from Streptomyces sp. YIM 66142

Streptomyces sp. YIM 66142 was cultivated in 250 mL Erlenmeyer flasks containing 50 mL of seed medium (0.4% yeast extract, 0.4% glucose, 0.5% malt extract, decavitamin, 0.03% alanine, pH 7.2). The flasks were shaken at 300 r.p.m. at 28 °C for 2 days using a rotary shaker. The seed culture (10%) was transferred into 1 L Erlenmeyer flasks containing 250 mL of fermentation medium (0.3% soybean powder, 2% glucose, 0.2% yeast extract, 0.5% starch, 0.2% peptone, 0.4% NaCl, 0.05% K₂HPO₄, 0.05% MgSO₄ and 0.2% CaCO₃, pH 7.2). The flasks were shaken at 300 r.p.m. for 6 days at 28 °C using a rotary shaker. The fermented whole broth (60 L) was centrifuged to separate the mycelia, and the fermented solution was extracted three times by an equivalent volume of EtOAc, to yield the EtOAc extract (29.1 g). The mycelia were extracted three times with acetone, yielding the acetone extract (8.0 g). The two extracts were then suspended in distilled H₂O and extracted three times with EtOAc, to concentrate the total sample in solution (13 g). This sample was separated into seven fractions (A1–A7) using a silica gel column with petroleum ether to MeOH. The fifth fraction, A5 (CHCl₃-MeOH 20:1), was separated using a Sephadex LH-20 column and eluted with methanol to yield six fractions (A5-I to A5-VI). Fraction A5-III was again fractionated with a Sephadex LH-20 column and eluted with methanol to obtain compound 2 (100 mg). Fraction A5-IV was subsequently separated into nine fractions (fractions A5-IV–I to A5-IV–IX) with a Sephadex LH-20 column. Fraction A5-IV–VI was further fractionated on silica gel with chloroform/acetone elution solvent (12:1–12:4, v/v) to obtain 1 (1.2 mg), and fraction A5-IV–VII was separated on silica gel with chloroform/methanol (45:1, v/v) to obtain 4 (1.5 mg). The A6 part was separated into four fractions (A6-I to A6-IV) using a Sephadex LH-20 column and eluted with methanol. The fraction A6-IV was again fractionated with a Sephadex LH-20 column and eluted with methanol to obtain 3 (4.2 mg) and 5 (5.1 mg).

Compounds 2, 3 and 5 showed no marked cytotoxicity on human leukemia cells (HL-60), human lung cancer cells (A549), hepatocellular carcinoma cells (SMMC-7721), human breast adenocarcinoma (MCF-7) or human colorectal carcinoma cells (SW480) at 40 μm. These compounds were tested for antimicrobial activities against five strains of microorganisms (B. subtilis, Staphylococcus aureus, Escherichia coli, Candida albicans and X. oryzae) at 512 μg mL⁻¹. Compounds did not show significant antibacterial activity except for 4 and 5 showed MICs of 32 μg mL⁻¹ against B. subtilis (Table 2). Much more potent inhibitory effect of herbicidins occurred against germination of the plant seeds, such as cabbage. The MICs of 8'-epi-herbicidin F (1), herbicidin F (2), herbicidin A (3), herbicidin B (4) and 2′-O-demethylherbicidin F (5) for germination of the seeds of cabbage were 12.5–50 , <3.1 , 3.1–12.5 , 12.5–50 and 12.5–50 μg mL⁻¹.

Table 2 MICs (μg mL⁻¹) of 1, 2, 3, 4 and 5 in screening of antimicrobial activity

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD