Phenylpropanoids from Liparis nervosa and their in vitro antioxidant and α-glucosidase inhibitory activities

Eleven phenylpropanoids were isolated from the whole grass of Liparis nervosa, an orchidaceous medicinal plant. Their structures were elucidated as (+)-Syringaresinol (1), (-)-Syringaresinol-4-O-β-D-glucopyranoside (2), Sinapaldehyde (3), Coniferyl aldehyde (4), Syringin (5), Sinapaldehye-4-O-β-D-glucoside (6), 2,3-dihydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (7), C-Veratroylglycol (8), 7S, 7′S, 8R, 8′R-icariol A2 (9), Erigeside 2 (10), and Methylsyringin (11) by comparing the spectroscopic data and physicochemical constants from the isolated compounds with the data reported in the literature. Compounds 1 and 9 were found to have potent in vitro antioxidant activities in the DPPH and ABTS assays, and their IC50 values were lower than those of vitamin C. More importantly, compound 9 had a strong α-glucosidase inhibitory activity with an IC50 value of 43.76 ± 2.03 µM, which was much lower than that of acarbose (IC50 = 273.12 ± 11.84 µM), indicating that compound 9 has the potential for the development of hypoglycemic drugs. In conclusion, the present study suggests that phenylpropanoids may be the additional representative type of active constituents in L. nervosa, which provides a new line of evidence to understand this medicinal plant.