A new antiviral isorhamnetin glycoside from the Tunisian plant Herniaria hirsuta L.

Herniaria hirsuta L. (Caryophyllaceae) is an annual herb known as hairy rupturewort. It is used in traditional medicine, particularly in North Africa, to prevent and cure kidney stones and as a diuretic. Rich in saponins, it possesses many other bioactive secondary metabolites including flavonoids and their glycosides. Plant specimens harvested in Tunisia were chemically investigated and their extracts tested for antiviral activity. Ethyl acetate and butanol extracts showed significant activity against Herpes Simplex type-2 (HSV-2) virus (IC50 = 31.15 μg/mL, SI =10.97 and IC50 = 46.04 μg/mL, SI = 6.44, respectively). Ultra-High Performance Liquid Chromatography-High Resolution ElectroSpray Ionization Mass Spectrometry (UHPLC-HRESIMS) analyses combined with Nuclear Magnetic Resonance (NMR) spectroscopy revealed the occurrence of a family of isorhamnetin glycosides, containing 1 to 3 sugar units. By using a bioassay guided fractionation approach, we identified a new flavonoid glycoside: its chemical structure was resolved by extensive use of NMR spectroscopy and HRESIMS/MS as isorhamnetin-3-O-(2-O-(4-acetyl)-α-L-rhamnopyranosyl, 6-O-α-L-rhamnopyranosyl)-β-D-galactopyranoside, which exhibited an IC50 = 20.34 μM (SI >15). Notably, its co-occurring deacetyl derivative resulted inactive. In vitro assays suggested that the antiviral action is exerted during the early stages of the viral cycle, preventing HSV-2 from infecting target cells.