Two Pairs of Enantiomeric Alkaloid Dimers from <i>Macleaya cordata</i>

Two pairs of enantiomeric alkaloid dimers, (±)-macleayins A (1) and B (2), representing a novel dimerization pattern of two different types of alkaloids via a C–C σ-bond, were isolated from the aerial parts of Macleaya cordata. The enantiomeric separation was achieved by chiral chromatography. Their structures and stereochemistry were determined by the analysis of extensive spectroscopic data, electronic circular dichroism calculation, and single-crystal X-ray diffraction data. (−)-Macleayin A exhibits modest cytotoxic activity against HL-60 cell line with the IC50 value of 3.51 μM.