Chemical Synthesis of Polygalacic Acid from Oleanolic Acid Enabled by Three Site-Selective C–H Oxidations

The first chemical synthesis of polygalacic acid was accomplished from readily available oleanolic acid through three complementary site-selective C–H oxidation reactions. Key transformations include palladium-catalyzed directed C–23 oxidation, base-promoted C–2 α-oxidation, and copper-mediated directed C–16 hydroxylation, enabling selective installation of three oxygen functionalities onto the pentacyclic triterpenoid scaffold. This work demonstrates an oxidation-based strategy for converting an abundant triterpenoid into a more highly oxygenated natural product.