Lignans from the root of Paeonia lactiflora and their anti-β-amyloid aggregation activities

Four new neolignans (1-4), together with two known lignans (5 and 6), were isolated from the root of Paeonia lactiflora. Compounds 1 and 2 were two racemates and were separated by chiral high performance liquid chromatography (HPLC) to give all of the four stereoisomeric forms sharing a common planar structure. Compounds 3 and 4 were two neolignan glycoside diastereomers but interestingly appeared to be enantiomers: they had the extremely similar (1)H and (13)C NMR spectra and had to be solved only by chiral HPLC. Their structures were determined by spectroscopic analysis, including 1D and 2D NMR, HRESIMS and electronic circular dichroism experiments. All compounds were evaluated for their inhibitory effects on β-amyloid aggregation, and the optical pure compound 2b was found to show the optimal Aβ(1-42) aggregation inhibition potency (81.1% at 20 μM). In addition, despite large amount of chemical studies performed on genus Paeonia, the lignans were reported for the first time.