Chiral separation of sesquineolignans from the stems and leaves of Neoshirakia japonica

Twelve pairs of sesquineolignan enantiomers (1a/1b−6a/6b and 1c/1d−6c/6d), including twenty one undescribed and three known (2b, 3b, and 4b) sesquineolignans were isolated from an ethanol extract of the stems and leaves of Neoshirakia japonica (Euphorbiaceae). The successful separation of twelve pairs of enantiomers with mirror image-like electronic circular dichroism (ECD) curves and opposite specific rotation values, as one of the most important steps in compound isolation, was carried out by chiral HPLC columns. The absolute configurations of all undescribed sesquineolignans were elucidated by comprehensive analysis of their experimental ECD spectra. The effects of all the isolates on antineuroinflammatory and radical scavenging activity were evaluated. Compared with the positive control minocycline (IC50 = 1.2 μM), compounds 1a/1b/1c/1d−6a/6b/6c/6d with IC50 values being greater than 50 μM displayed almost no effect on the inhibition of NO production in LPS-induced BV-2 microglial cells. The results of DPPH-radical scavenging activity for them showed that compound 3c had moderate radical scavenging ability (EC50 = 48.47 μM), while the EC50 value of positive control vitamin C was 18.21 μM.