New Bioactive Prenylflavonoids and Dibenzocycloheptene Derivative from Roots of Dendrolobium lanceolatum

Two new flavanones (1 and 2), a new flavan (3), and a new rare dibenzocycloheptene derivative (4) together with a known flavan, 4‘-hydroxy-2‘ ‘,2‘ ‘dimethyl-pyranoflavan (5), were isolated from the roots of Dendrolobium lanceolatum. Their structures were established on the basis of spectral evidence, and an X-ray analysis was performed to confirm the structure of 4. Compounds 1−3 exhibited antimalarial activity with IC50 values of 2.6, 3.3, and 3.1 μg/mL, respectively. Compounds 1−5 showed moderate antimycobacterial activity with MIC values of 6.3, 12.5, 25, 25, and 50 μg/mL, respectively. In addition, 1 showed strong cytotoxicity against cancer cell lines KB, BC, and NCI-H187 with IC50 values of 1.2, 1.6, and 0.6 μg/mL, respectively, while 2 showed moderate cytotoxicity against the NCI-H187 cell line with an IC50 value of 8.1 μg/ mL.