Despite their structural similarities, the natural products chelerythrine (5) and sanguinarine (6) target different binding sites on the pro-survival Bcl-XL protein. This paper details the synthesis of phenanthridine-based analogues of the natural products that were used to probe this difference in binding profiles. The inhibitory constants for these compounds were then measured in a fluorescence polarization assay against Bcl-XL and the tagged Bak-BH3 peptide. The results led to structure−activity relationship studies, which identified the structural motifs required for binding-site specificity as well as inhibitory activity. We also identified synthetic analogues of the natural products that display similar binding modes but with more potent IC50 values.
