Discovery of diterpenoid and sesquiterpenoids as α-glucosidase inhibitors from the leaves of Pieris formosa

Two new compounds, a norditerpenoid and a megastigmane sesquiterpenoid, were isolated from the ethyl acetate extract of Pieris formosa leaves collected in Yichang, Hubei, China, together with eight known megastigmane sesquiterpenoids. Their structures were elucidated by spectroscopic data analysis and electronic circular dichroism (ECD) calculations. Pormoside A ( 1 ) represents the first example of a 17- β - D -glucopyranosyloxy-substituted 14,15-di- nor -cyclophytane diterpenoid. All isolates were evaluated for α -glucosidase inhibitory activity. Pormoside A ( 1 ) (IC 50 = 112.90 ± 3.98  μ M) showed significantly more potent inhibition than the positive control acarbose (IC 50 = 219.55 ± 3.95  μ M). Molecular docking studies of pormoside A and B further revealed their binding interactions with α -glucosidase.