The Structures of Claudimerines-A and -B, Novel Bicoumarins from Citrus hassaku

Two novel dimeric coumarins, claudimerin-A (1) and -B (3), were isolated from the roots of Citrus hassaku (Rutaceae). The chemical structures were elucidated by spectroscopic studies and/or single-crystal X-ray analysis. The main structural characteristic is a pyranopyran ring connecting two clausarin (2) units.