Total Syntheses and Anti-inflammatory Evaluations of Pongamosides A–C, Natural Furanoflavonoid Glucosides from Fruit of Pongamia pinnata (L.) Pierre

The syntheses of three natural furanoflavonoid glucosides, including two flavone glucosides, pongamosides A (1) and B (2), and a flavonol glucoside, pongamoside C (3), were achieved for the first time in 9-15 steps from commercially available materials in overall yields ranging from 2.9% to 29%. The synthetic sequence featured a NaH-promoted BK-VK rearrangement and acid-catalyzed intramolecular cyclization to furnish the furanoflavonoid aglycone. Meanwhile, phase-transfer-catalyzed glycosylation and Schmidt's trichloroacetimidate procedure were employed to establish the pivotal O-glycosidic linkage. The anti-inflammatory activities of compounds 1-3, as well as their aglycones 5a, 5b, and 23, were determined against NO production in the LPS-stimulated RAW264.7 cells. The results indicated that the O-glycosylation may reduce the anti-inflammatory activity of furanoflavonoid in vitro.