A study of the chemical constituents of the leaves of Clausena excavata cultivated
in a greenhouse led to the isolation and identification of 10 new furanone-coumarins
named clauslactones A (1), B (2), C (3), D (4), E (5), F (6), G (7), H (8), I (9),
and J (10), together with a known carbazole, clauszoline M, and a coumarin, umbelliferone.
The new coumarins contain a C(10) terpenoid side chain with a furanone (gamma-lactone)
moiety. Further, in clauslactones A-D (1-4), the terpenoid side chain was shown to
be linked to the 7,8-dioxygenated coumarin skeleton through a 1, 4-dioxane ring system.
This is the first example of coumarins with these structural characteristics in nature.
These furanone-coumarins were found to exhibit inhibitory activity against 12-O-tetradecanoylphorbol-13-acetate-induced
Epstein-Barr virus early antigen activation in Raji cells.