Analysis and action of cnicin

Abstract

Cnicin, a sesquiterpenlactone of germacranolide-type, reacts with polynitroaromatic compounds in alkaline medium to form intensely coloured products of the Meisenheimer complex-type. A propenide complex results from the addition of excess picrate (Baljet reagent), which is stable enough for photometric cnicin determination. Dried leaves of Cnicus benedictus L. (Blessed Thistle, Asteraceae) contain up to 2.5% of cnicin and commercial herbs between 0.2-0.7%. Shoots and flowering heads are almost free from this bitter substance. Storage of dried plant material leads to high losses due to the instability of cnicin. The approximate acute toxicity (ALD50) for mice, orally administered, is 1.6-3.2 mmol cnicin/kg body weight. Cnicin shows an antiinflammatory activity in the rat paw edema screen which is nearly equivalent to that of indomethacin. Intraperitoneal application of cnicin results in a strong irritation of tissue. In the writhing-test, cnicin causes abdominal pain in mice with an ED50 of 6.2 µmol/kg body weight.