Ambidalmines A–E and ambidimerine F: Bioactive dihydrobenzophenanthridine alkaloids from Corydalis ambigua var. amurensis

Ten new scarce dihydrobenzophenanthridine alkaloids, including seven monomers, ambidalmines A1/2, B1/2–E (1a/b, 2a/b–5), and three dimers, ambidimerines F1 (6a), F2 (6b) and F3 (6c), were isolated from the tubers of Corydalis ambigua var. amurensis. All of these compounds were discovered in the forms of enantiomers. The structures were elucidated based on extensive spectroscopic analysis, with absolute configurations of the enantiomeric compounds assigned by single-crystal X-ray diffraction analysis, circular dichroism (CD) and optical rotations. Bioactivity evaluation showed that compounds 1a, 2a, 2b and 6b exhibit comparable protective effects on hypoxic H9C2 cells.