Antiproliferative Pterocarpans and Coumestans from Lespedeza bicolor

Chromatographic purification of a methanol extract of the roots of Lespedeza bicolor led to the isolation of four new pterocarpans (1–4), two new coumestans (6 and 7), two new arylbenzofurans (8 and 9), and the known pterocarpan 1-methoxyerythrabyssin II (5). Their structures were identified using NMR spectroscopy, UV spectroscopy, and mass spectrometry. Cytotoxicity assays showed that compounds 1–9 exerted antiproliferative effects on blood cancer cells. Of these compounds, 1 and 6 induced mitochondrial depolarization and induced apoptosis in Jurkat cells. These compounds promoted cell death by inducing cell-cycle arrest at the G1 stage, reducing levels of BCL2, and increasing cleavage of PARP-1. These findings indicate that 1 and 6 are possible lead compounds for the treatment of human leukemia cells via intracellular signaling.