Unexpected novel pheophytin peroxides from the leaves of Biden pilosa

Two new pheophytins, bidenphytins A (1) and B (2), with peroxide functionalities on ring E, were isolated from Biden pilosa LINN. var. radiata SCH. III P., a popular Taiwanese folk medicine. Also isolated were the following six known compounds: pheophytin a (3), (13(2)R)-13(2)-hydroxypheophytin a (4), (13(2)S)-13(2)-hydroxypheophytin a (5), (13(2)R)-13(2)-hydroxypheophytin b (6), (13(2)S)-13(2)-hydroxypheophytin b (7), and aristophyll-C (8). Their structures were elucidated by spectroscopic methods (UV, IR, 1D- and 2D-NMR) and by mass spectrometry (HR-FAB-MS). Possible biosynthetic pathways for 1 and 2 are proposed.