Cnicin is a sesquiterpene lactone

Sesquiterpene lactone

Sesquiterpene lactones are a class of chemical compounds; they are sesquiterpenoids and contain a lactone ring, hence the name....

, esterified with a substituted acrylic acid

Acrylic acid

Acrylic acid is an organic compound with the formula CH2=CHCO2H. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has a characteristic acrid or tart smell. It is miscible with water, alcohols,...

, and belonging to the germacranolide

Germacranolide

Germacranolides are a group of natural chemical compounds classified as sesquiterpene lactones. They are found in a variety of plant sources....

 class of natural products. It is mainly found in Cnicus

Cnicus

Cnicus benedictus , was the sole species in the genus Cnicus, but has been reclassified as Centaurea benedicta...

 (Cnicus benedictus L. (Asteraceae

Asteraceae

The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...

)), and is present in spotted knapweed

Centaurea maculosa

Centaurea maculosa, the spotted knapweed, is a species of Centaurea native to eastern Europe.It has been introduced to North America, where it is considered an invasive plant species in much of the western United States and Canada. In 2000, C. maculosa occupied more than in the US.Knapweed is a...

plants, where highest and lowest concentrations are found in the leaves (0.86-3.86% cnicin) and stems respectively. Cnicin is used as a bitter tonic and the bitterness value is approximately 1,500.