New 8-O-4' Neolignans and Their Antibacterial Activity from the Whole Plants of Clematis lasiandra

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.