Neuraminidase inhibitors from Caragana sinica (Buc'hoz) Rehder roots.

Two new oligostilbenes, caragasinins D (1) and E (2), along with four known compounds, kobophenol A (3), α-viniferin (4), wistin (5), and 5-hydroxy-2-[2-(4-hydroxyphenyl)acetyl]-3-methoxylbenzoic acid (6) were isolated from Caragana sinica roots. These compounds were spectroscopically analyzed for their structure and stereochemistry and compared with existing data. The configurations of 1 and 2 were elucidated by 1H nuclear magnetic resonance spectroscopy, circular dichroism spectroscopy, and time-dependent density-functional theory simulated electronic circular dichroism spectral data. All six compounds were evaluated for their inhibitory activity against neuraminidase (NA) from Clostridium perfringens. Among the tested compounds, 5-hydroxy-2-[2-(4-hydroxyphenyl)acetyl]-3-methoxylbenzoic acid (6) demonstrated statistically significant NA inhibitory activity, which was comparable to the positive control, mangiferin.