Two New Alkaloids from Brachystemma calycinum and Their Inhibitory Effects on Lymphocyte Proliferation

Abstract Two new alkaloids, brachystemidines F ( 1 ) and G ( 2 ), were isolated from the roots of Brachystemma calycinum. Their structures were established on the basis of detailed spectroscopic analyses, including extensive NMR and HR‐MS techniques. Compound 2 , which exhibits an unusual N ‐hydroxydiazenyl (HONN) moiety, is a potent immunosuppressive agent, as demonstrated by inhibition of mouse T‐ and B‐lymphocyte proliferation, with IC 50 values of 6.33 and 5.60 μg/ml, resp.