Monoterpene indole glycoalkaloids from the hook-bearing branches of Uncaria rhynchophylla

Twelve monoterpene indole glycoalkaloids, comprising of three new ones, 19-epi-rhynchophylloside A (1), 7-epi-rhynchophylloside A (2), and 7-epi-anthocephalusine A (3), were isolated from the hook-bearing branches of Uncaria rhynchophylla. The structures and absolute configurations of 1-3 were elucidated by analysis of MS, NMR, ECD, and single-crystal X-ray diffraction or TDDFT-ECD calculations. Glycoalkaloids 1 and 3 showed significant immunosuppressive activity against the proliferation of B lymphocyte induced by LPS with broad selective index.