Three quinolizidine dimers from the seeds of Sophora alopecuroides and their hepatoprotective activities

Sophoralines A–C, three novel [2 + 2] cycloaddition dimers of matrine-based alkaloids with an unprecedented 6/6/6/6/4/6/6/6/6 nonacyclic skeleton containing 11 stereogenic centers, were isolated from Sophora alopecuroides. Their structures were determined by spectroscopic methods, and the absolute configurations were further determined by single-crystal X-ray diffraction analysis for 1 and quantum chemical calculations of electronic circular dichroism (ECD) spectra for 2 and 3. Moreover, 1 exhibited excellent hepatoprotective activities in acetaminophen-induced liver injury in vitro and in vivo.