Bioassay-Guided Isolation of an Abetiane-Type Diterpenoid from <i>Prunella vulgaris</i> That Protects against Concanavalin A-Induced Autoimmune Hepatitis

Abstract

<i>Prunella vulgaris</i> is a widely used edible Chinese medicinal plant. In the present study, two new abietane-type diterpenoids, abietoquinones A (<b>1</b>) and B (<b>2</b>), were isolated from this plant by an immunosuppressive bioassay-guided isolation procedure. Their structures were elucidated unambiguously by NMR spectroscopic analysis, single-crystal X-ray crystallography, and electronic circular dichroism calculations. Compounds <b>1</b> and <b>2</b> bear a cyclohex-2-ene-1,4-dione moiety, which is uncommon among abietane diterpenes. Also, abietoquinone A (<b>1</b>) suppressed murine splenocyte proliferation and decreased the production of proinflammatory cytokines induced by concanavalin A (Con A) in vitro. In Con A-challenged mice, preinjection with <b>1</b> significantly ameliorated liver injury. Additionally, abietoquinone A (<b>1</b>) exhibited inhibitory activities against the proliferation of murine splenocytes and human T cells induced by anti-CD3/anti-CD28 monoclonal antibodies (mAbs).