Flavonoids from the leaves of Cryptocarya chinensis with antituberculosis activity
Cryptocarya chinensis (Hance) Hemsl. (Lauraceae) is a medium-sized evergreen tree, distributed throughout southern China, Japan, and Taiwan. Flavonoids, pyrones, pavines, aporphines, benzylisoquinolines, lignans, and their derivatives are widely distributed in plants of the genus Cryptocarya, and many of these compounds exhibit cytotoxic and antioxidant activities. In our continuing studies on the antitubercular constituents of Formosan plants, over 400 species have been screened for in vitro antituberculosis activity to date, and C. chinensis has been found to be one of the active species. Studies on the neutral CHCl3 fraction of leaves from this species has led to the isolation of two new tetrahydroflavanones, cryptochinone G (1) and cryptochinone H (2), and two new flavanones, crytoflavanone A (3) and crytoflavanone B (4), together with 8 known compounds (5-12). The structures of these new compounds were determined through spectroscopic analyses, including extensive 2D-NMR, ORD, MS and, IR. Among the isolates, cryptocaryone (5), cryptocaryanone B (6), and pinocembrin (7) showed antituberculosis activities with MICs of 25.0, 25.0 and 3.5 ug/mL against Mycobacterium tuberculosis, respectively. The structural elucidation of 1-4 and the antituberculosis activities of the isolates will be discussed in this symposium.