Chemical constituents from Artemisia rupestris and their neuraminidase inhibitory activity.

Two new thiophene derivatives (1 and 2), a new sesquiterpene (3), and 15 known compounds (4-18) were isolated from the whole plants of Artemisia rupestris. The new compounds (1-3) were elucidated by extensive spectroscopic techniques including 1 D (1H and 13C) and 2 D NMR experiments (COSY, HSQC, HMBC and NOESY), and HR-ESI-MS. Most of the isolates (1-6, 8, 10-18) exhibited the neuraminidase inhibitory activity with IC50 values ranging from 74.07-986.54 µM by a fluorescence-based assay. Two known flavonoids (chrysosplenetin B and luteolin) showed a comparable activity to oseltamivir acid on neuraminidase inhibition.

Development of a thin-layer chromatography bioautographic assay for neuraminidase inhibitors hyphenated with electrostatic field induced spray ionisation-mass spectrometry for identification of active Isatis indigotica root compounds.

The identification of neuraminidase inhibitors from natural products is a promising strategy in the field of anti-influenza research. In this study, a new thin-layer chromatography (TLC) bioautographic assay for the screening of neuraminidase inhibitors from natural products was developed. This TLC bioassay is based on the one-step reaction of neuraminidase with the sodium salt of 5­bromo­4­chloro­3-indolyl-α-d-N-acetylneuraminic acid (substrate) and the subsequent formation of blue coloured products. Neuraminidase inhibitory activity was shown by the development of white spots against the blue TLC background. The key factors affecting the assay (such as enzyme concentration, substrate concentration, incubation time, reaction time, and pH) were investigated and optimised by a combination of a one-factor-at-a-time design and a Box-Behnken design/response surface method. The developed TLC bioautographic method was applied to identify neuraminidase inhibitory compounds in the roots of Isatis indigotica. Eleven active compounds including six alkaloids, three lignans, one sterol, and one fatty acid were identified in situ by direct coupling with an electrostatic field induced spray ionisation-mass spectrometry approach through analysis of their MSn (n = 4) data or comparison with reference substances. The developed TLC bioautographic assay is simple, rapid, and efficient for screening potential neuraminidase inhibitors from natural products.