Ophiorrhines A and B, Two Immunosuppressive Monoterpenoid Indole Alkaloids from Ophiorrhiza japonica

Two monoterpenoid indole alkaloids, ophiorrhines A (1) and B (2), were obtained from plant Ophiorrhiza japonica BI. Their structures were elucidated by extensive spectroscopic methods and single crystal X-ray diffraction. Compounds 1 and 2 possess a novel spirocyclic ring system. Its biosynthesis pathway is proposed. Compound 2 exhibits potent inhibitory activity against concanavalin A (Con A) induced T cell proliferation and lipopolysaccharide (LPS) induced B lymphocyte cell proliferation with IC₅₀ values 13.3 and 7.5 μM, respectively. Compound 1 exhibits significant inhibition specifically against the LPS-induced proliferation of B lymphocyte cells with IC₅₀ value 18.6 μM.