Bioactive A-Type Proanthocyanidins from Cinnamomum cassia

Two trimeric proanthocyanidins, cinnamtannin B-1 (1) and cinnamtannin D-1 (2), have been isolated from the bark of Cinnamomum cassia along with the known tetramer parameritannin A-1 (3) and a previously unreported tetramer, named cassiatannin A (4). The structures of 14 were elucidated on the basis of 1D and 2D NMR, MS, and CD analyses and compared to the reported data. Proanthocyanidins (14) possess significant in vitro inhibitory activity against cyclooxygenase-2 (COX-2) at micromolar concentrations.