Major antitermitic components of the heartwood of southern catalpa

The heartwood of southern catalpa,Catalpa bignonioides Walt., is resistant to attack by the eastern subterranean termiteReticulitermes flavipes (Kollar), but extraction with a ternary solvent mixture of acetone-hexanewater (54∶44∶2) by volume removed the antitermitic characteristics from the heartwood. Four compounds comprised approximately 98% of the antitermitic fraction of the extract: the sesquiterpene alcohol, catalponol (67%); its epimer, epicatalponol (5%); a structurally related ketone, catalponone (1%); and the phthalide, catalpalactone (25%). Pure compounds were isolated by semipreparative scale reversed-phase HPLC and identified by GC-MS and UV spectroscopy. The structure of catalponol was further confirmed by the formation of derivatives. Bioassays indicated that catalponol had the greatest toxicity in cellulose pad tests, but in tests using vacuum impregnation of these compounds into termite-susceptible wood blocks at levels approximating those found in catalpa heartwood, catalpalactone exhibited the highest antitermitic activity.