Acetylcholinesterase Inhibitory Alkaloids from the Whole Plants of Zephyranthes carinata

Eleven new alkaloids (1–11), classified as the 12-acetylplicamine (1), N-deformyl-seco-plicamine (2), plicamine (3–6), 4a-epi-plicamine (7), seco-plicamine (8), and lycorine (9–11) framework types, along with 15 known alkaloids (12–26) were isolated from the whole plants of Zephyranthes carinata. The structures of the new alkaloids 1–11 were established by extensive spectroscopic data interpretation. The absolute configurations of 9 and 10 were defined by single-crystal X-ray diffraction analysis. Zephycarinatines A (1), B (2), and G (7) represent the first examples of 12-acetylplicamine, N-deformyl-seco-plicamine, and 4a-epi-plicamine alkaloids, respectively. Alkaloids 6, 11, 17, and 20–23 exhibited AChE inhibitory activities with IC50 values ranging from 1.21 to 184.05 μM, and a preliminary structure–activity relationship is discussed.