Synthesis of Procyanidin B3 and Its Anti-inflammatory Activity. The Effect of 4-Alkoxy Group of Catechin Electrophile in the Yb(OTf)3-Catalyzed Condensation with Catechin Nucleophile

Yb(OTf)3-catalyzed equimolar condensation of the benzylated catechin with various 4-alkoxy catechin derivatives was studied. In particular, the reaction using 4-(2′′-ethoxyethoxy)flavan derivative gave good yield with excellent stereoselectivity. The condensed product was successfully converted to procyanidin B3 (1). The anti-inflammatory effect of procyanidin B3 (1) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation of mouse ears was examined. The anti-inflammatory activity of 1 was stronger than that of indomethacin and glycyrrhetinic acid, the normally used anti-inflammatory agents.