New dihydrodibenzoxepins from Bulbophyllum kwangtungense

Three new dihydrodibenzoxepins 7,8-dihydro-5-hydroxy-12,13-methylenedioxy-11-methoxyldibenz[ B,F]oxepin (1), 7,8-dihydro-4-hydroxy-12,13-methylenedioxy-11-methoxyldibenz[ B,F]oxepin (2), and 7,8-dihydro-3-hydroxy-12,13-methylenedioxy-11-methoxyldibenz[ B,F]oxepin (3), were isolated from Bulbophyllum kwangtungense Schlecht, along with three known compounds, cumulatin (4), densiflorol A (5) and plicatol B (6). Their structures were established by a combination of 1D and 2D NMR spectroscopic techniques. All new compounds (1-3) and the known compound densiflorol A (5) exhibited anti-tumor activities against HeLa and K562 human tumor cell lines.