Chem. Pharm. Bull. 54(1) 103—106 (2006)

belonging to the family Compositae which comprises about 1000 genera and 20000 species. S. marianum is common in Kashmir at an altitude of 1800—4000 m and is cultivated for ornaments in gardens. The plant is used in the treatment of hepatitis, cirrhosis, regeneration from liver diseases, and liver poisoning. A decoction of this plant is also used by the local physicians for the treatment of a variety of viral diseases. A literature survey revealed that twenty compounds have so far been reported from S. marianum. The major constituents are, however, flavonoids, flavanolignans, diterpenes and flavanoglycosides. The ethnopharmacological and chemotaxonomic importance of the genus Silybum prompted us to investigate the chemical constituents of S. marianum. A methanolic extract of this plant showed strong toxicity in the brine shrimp lethality test, revealing the possible presence of bioactive compounds. Further pharmacological screening revealed significant inhibitory activity against the enzyme chymotrypsin. The inhibitory activity was most pronounced in the chloroform-soluble fraction. This prompted us to carry out bioassay-guided isolation of bioactive compounds from this fraction. As a result of these studies we have isolated marianine, a new lanostane-type triterpene (1) and marianosides A (2) and B (3), two new triterpenoidal glucosides, respectively. All three showed significant chymotrypsin inhibiting activity. This is the first report of the natural occurrence of lanostane-type triterpenes in the genus Silybum.