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.