A pair of heterodimeric isoquinoline alkaloid enantiomers, (±) thaliberberine A, five new thalifaberine-type aporphine-benzylisoquinoline (ABI) alkaloids, thalicultratines M-Q, and thirteen known analogues were isolated from the roots of Thalictrum baicalense Turcz. ex Ledeb. The structures were determined by extensive spectroscopic methods and ECD calculations. Thaliberberine A featuring a novel carbon skeleton coupled by two different classes of isoquinoline alkaloids, protoberberine and phthalidoisoquinoline, represents the first natural product with the berberine skeleton substituted at C-6. Plausible biosynthetic routes of 1 are proposed. All isolated alkaloids were screened for their antiproliferative effects in vitro against HCT116, Caco-2, and HepG-2 cancer cell lines. The most active ABI alkaloid, thalifaronine (7) induced G0/G1 cell cycle arrest and apoptosis. Compound 7 effectively inhibited the colony formation and tumor growth of HCT116 cells in xenografts. The thalifaberine-type ABI dimers represent a group of compounds with antitumor activity. The spectroscopic characteristics of thalifaberine-type ABI dimers were also analyzed.
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