Ophiorrhines F and G, Key Biogenetic Intermediates of Ophiorrhine Alkaloids from Ophiorrhiza japonica and Their Immunosuppressant Activities.

Continued interest in bioactive alkaloids led to the isolation of two undescribed alkaloids, ophiorrhines F ( 1 ) and G ( 2 ), from the aerial parts of Ophiorrhiza japonica. Their structures were elucidated based on spectroscopic methods, electronic circular dichroism, and calculated NMR with DP4+ analysis. These two alkaloids represent key biological genetic intermediates in the formation of ring C in the ophiorrhines. Compound 1 exhibited good inhibition on LPS-induced B cell proliferation with an IC ₅₀ value of 0.38 μM and showed significant selective inhibitory activity on a B cell proliferation response with a selective index of 548.42. A preliminary study indicated that 1 may have a new mechanism of immunosuppression.