New binary coumarins from Citrus plants.

Two new binary coumarins, khelmarin-A (1) and -B (2), were isolated from root bark of Poncirus trifoliata which had been used as a rootstock of Citrus Hassaku (hassaku), and roots of original seedlings of Citrus canariculata (kiku-daidai), respectively. The structurs of the new binary coumarins 1 and 2 contain cis-khellactone (3) as a common structural component, which is linked with a nordentatin (5) or a xanthoxyletin (6) unit, respectively.