Total Syntheses and Anti-inflammatory Evaluations of Karanjin and its Natural Analogues

Karanjin (1) is a natural furanoflavonol derivative isolated from seeds of Pongamia pinnata (L.) Pierre. In this paper, we have accomplished a concise total synthesis of karanjin (1) as well as its natural analogues pongapinnol D (2), 3-hydroxy-6-methoxy-2-phenyl-4H-furo[2,3-h]-1-benzopyran- 4-one (3) and 3,6-dimethoxy-2-phenyl-4H-furo[2,3-h]chromen-4-one (4). One-pot aerobic oxidation was the key step to afford the flavonol framework under mild conditions. The anti-inflammatory properties of synthesized 1–4 were determined against NO production in the LPS-stimulated RAW264.7 cells.