The antagonistic effects of khellactones on platelet-activating factor, histamine, and leukotriene D4.

Khellactones of Peucedanum praeruptorum DUUN., including praeruptorins A (= Pd-Ia, 2) and B (= Pd-II,11), had an antagonistic effect specifically on platelet aggregation induced by platelet activating factor (PAF) among various aggregating agents examined, and represent a new class of PAF antagonists. We examined the effects of twenty compounds on PAF-induced platelet aggregation and on histamine- and leukotriene D4 (LTD4)-induced contractions in isolated guinea pig ileum. Compounds 2, (+/-)-cis-3',4'-diacetylkhellactone (3), (+/-)-cis-4'-acetyl-3'-crotonoylkhellactone (5), (+/-)-cis-4'-acetyl-3'-tetrolylkhellactone (6), (+/-)-cis-4'-acetyl-3'-tigloylkhellactone (7), (+/-)-cis-4'-acetyl-3'-(2"-methylbutyryl)khellactone (8), (+/-)-cis-3',4'-ditigloylkhellactone (10), and 11 all strongly inhibited PAF-induced platelet aggregation. (+/-)-cis-4'-Acetyl-3'-(2"-methyl-2"-dodecenoyl)khellactone (9), (+/-)-cis-4'-ethyl-3'-tigloylkhellactone (13), (+/-)-cis-4'-ethyl-3'-[N-(2"-triethylammonio)ethylcarbamoyl] khellactone iodide (16), (+/-)-trans-3',4'-diacetylkhellactone (18), (+/-)-trans-4'-acetyl-3'-crotonoylkhellactone (19), (+/-)-trans-4'-acetyl-3'-valerylkhellactone (20), (+/-)-trans-4'-acetyl-3'-isovalerylkhellactone (21), and (+/-)-trans-4'-acetyl-3'-tigloylkhellactone (22) were weakly inhibitory. Most of the compounds exhibited noncompetitive antagonist actions on histamine- and LTD4-induced contractions.(ABSTRACT TRUNCATED AT 250 WORDS)