Identification of a Novel Casbane-Type Diterpene Phytoalexin,ent-10-Oxodepressin,from Rice Leaves

(+)-Haedoxan A, an insecticidal sesquilignan, inhibited the specific binding of the noncompetitive GABA antagonist ³⁵S]t-butylbicyclophosphorothionate (TBPS) to rat brain membranes in concentration-dependent and noncompetitive manners. The data show haedoxan’s interaction with a site coupled to the TBPS-binding site on the GABA_A receptor in rat brain, while the physiological significance of the interaction remains to be discovered.