New 8-O-4′ Neolignans and Their Antibacterial Activity from the Whole Plants of <i>Clematis lasiandra</i>

Abstract

Four new 8-O-4′ neolignans, characterized at methoxy or ethoxy groups substituted at C-7, namely, (±) lasiandranins A–D (1–4), and two known analogs (±) pinnatifidanin BV (5) and (±) pinnatifidanin BVI (6) were isolated from the whole plants of Clematis lasiandra Maxim. The structures of 1–6 were determined by spectroscopic methods including 1D, 2D NMR, ECD, and HRESIMS analysis. Compounds 1 and 5 were determined as erythro configuration, while 2–4 and 6 were determined as threo configuration based on the chemical shift difference of H-9a and H-9b in CD3OD. The 8-O-4′ neolignans were found from the genus Clematis for the first time. Compounds 1–6 were evaluated for their antibacterial activity against three plant pathogenic bacteria Pseudomonas syringae pv. actinidiae, Ralstonia solanacearum, and Erwinia carotovora by agar and broth dilution methods. Compounds 1–6 showed potent antibacterial activity against R. solanacearum with MIC values of 25–50 μg/mL and relatively lower activity against P. syringae pv. actinidiae with MIC values of 50–100 μg/mL, while they were inactive to E. carotovora.