Pseudorabies virus (PRV) is a pathogen that causes Aujeszky’s disease (AD) in animals, leading to huge economic losses to swine farms. In order to discover anti-PRV compounds, we studied the extracts of the strain Streptomyces jiujiangensis NBERC-24992, which showed significant anti-PRV activity. Eight benzoheterocyclic secondary metabolites, including three new compounds (1–3, virantmycins D–G) and five known compounds (4–8, virantmycin, A-503451 D, A-503451 D acetylate, A-503451 A, and A-503451 B), were isolated from the broth of NBERC-24992. The structures of the new compounds were identified by using extensive spectroscopic data, including mass spectrometry (MS), nuclear magnetic resonance (NMR), and electronic circular dichroism (ECD). Compound 1 was found to be a novel heterocyclic compound with a tricyclic skeleton from natural product. All compounds were tested for antiviral activity, and 4 (virantmycin) showed an excellent effect against PRV and was better than ribavirin and acyclovir. Our study revealed that chlorine atom and tetrahydroquinoline skeleton were important active moiety for antiviral activity. Virantmycin could be a suitable leading compound for an antiviral drug against PRV.

Two new napyradiomycins derivatives, napyradiomycin A4 (1) and A80915 H (2), along with five known ones, were isolated from the ethyl acetate extract of fermentation culture of Streptomyces kebangsaanensis WS-68302. Their structures were elucidated by extensive spectroscopic analysis, including HR-MS, 1D and 2D NMR, CD spectrum, as well as comparison with literature data. Compound 1 exhibited significant antiviral activity against PRV (Pseudorabies virus) with an IC₅₀ value of 2.056 μM and therapeutic ratio at 14.98, suggesting that it might have potential for development of an antiviral agent. Moreover, compound 1 displayed the strongest inhibition against PRV protein among the tested napyradiomycins in the indirect immunofuorescence assay. Compounds 3 and 4 showed higher activities against swine pathogenic Streptococcus suis than the positive control penicillin G sodium salt, with MIC values of 3.125 and 6.25 μg/mL, respectively. Compounds 1 and 3–6 exhibited moderate antibacterial activity against the swine pathogenic Erysipelothrix rhusiopathiae, with MIC values ranging from 25 to 50 μg/mL.