Azulenofurans

Helenalin, or (-)-4-Hydroxy-4a,8-dimethyl-3,3a,4a,7a,8,9,9a-octahydroazuleno[6,5-b]furan-2,5-dione, is a toxic sesquiterpene lactone which can be found in several plants such as Arnica montana and Arnica chamissonis Helenalin is responsible for the toxicity of the Arnica spp. Although toxic, helenalin possesses some in vitro anti-inflammatory and anti-neoplastic effects. Helenalin can inhibit certain enzymes, such as 5-lipoxygenase and leukotriene C4 synthase. For this reason the compound or its derivatives may have potential medical applications.

Lactucin is a bitter substance that forms a white crystalline solid and belongs to the group of sesquiterpene lactones. It is found in some varieties of lettuce and is an ingredient of lactucarium. It is also found in dandelion coffee. It has been shown to have analgesic and sedative properties, which are speculated to occur via modulation of the GABAA receptor, as well as antimalarial activity.

Thapsigargin is a non-competitive inhibitor of the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA). Structurally, thapsigargin is classified as a guaianolide, and is extracted from a plant, Thapsia garganica. It is a tumor promoter in mammalian cells.

Lactucopicrin (Intybin) is a bitter substance that has a sedative and analgesic effect, acting on the central nervous system. It is a sesquiterpene lactone, and is a component of lactucarium, derived from the plant Lactuca virosa (wild lettuce), as well as being found in some related plants such as Cichorium intybus. It is also found in dandelion coffee.