Urushiol

Urushiols are a group of solid or oily chemical compounds in Sumachgewächsen such as poison ivy Toxicodendron quercifolium, especially in various Rhus species such as poison ivy ( Toxicodendron radicans, English poison ivy ), poison oak ( Toxicodendron diversilobum, English poison oak, in American literature also the Toxicodendron quercifolium ) and lacquer tree Rhus occur verniciflua. The class is named after its occurrence in the sap of the lacquer tree, which called Urushi also a Japanese crafts.

Structure, representatives and properties

Chemically, it is at Urushiolen derivatives of 1,2- dihydroxybenzene ( catechol ). To the central catechol is a saturated alkyl -(3- Alkylbrenzcatechine ) alkenyl substituent or unsaturated (3- Alkenylbrenzcatechine ) is attached in each case. In the poisonous plants always comes before a mixture of different urushiols, where - different depending on the plant species - usually the urushiol I and III constitute the main ingredient. We identified about 15 substances, the saturated urushiol I is the only representative of a solid. Used as the lacquer of the lacquer tree Toxicodendron vernicifluum extracted mixture is a yellow, oily liquid having a boiling point of 200-210 ° C.

All urushiols are only minimally soluble in water but well in alcohols and diethyl ether. The unsaturated representatives II to V tend to polymerize. Solutions in methanol or ethanol can be oxidized at room temperature by atmospheric oxygen to the corresponding ortho -quinones.

Biological Properties

Urushiols are extremely potent allergens; by Uroshiole from poison ivy ( poison ivy ) and oak ( poison oak ) triggered contact allergies are the most common form of allergy in the United States. The toxic effect of the substances is based on the inhibition of prostaglandin biosynthesis. In vitro studies with preparations from sheep seminal vesicles at low concentrations showed (37 micromoles / l of an extract of Rhus radicans ) a complete inhibition of prostaglandins.

Allergy -induced contact dermatitis, and are dependent on the chemical structure of urushiols. In North America where most of the cases described, it has been observed that the skin reaction depend on the degree of saturation of the alkyl groups. In most individuals are allergenic urushiols having at least two double bonds and less than half respond to urushiols with only saturated alkyl groups. This is a real allergy is mediated by T lymphocytes antigen. The reaction occurs only with prior sensitization. In 50 to 70% of the North American population this allergy can be triggered.