Piperine

Piperine, possibly along with its isomer chavicine, is the compound responsible for the pungency of black pepper and long pepper. It has been used in some forms of traditional medicine.

Preparation
Due to its poor solubility in water, piperine is typically extracted from black pepper by using organic solvents like dichloromethane. The amount of piperine varies from 1–2% in long pepper, to 5–10% in commercial white and black peppers.

Piperine can also be prepared by treating the solvent-free residue from a concentrated alcoholic extract of black pepper with a solution of potassium hydroxide to remove resin (said to contain chavicine, an isomer of piperine). The solution is decanted from the insoluble residue and left to stand overnight in alcohol. During this period, the alkaloid slowly crystallizes from the solution.

Piperine has been synthesized by the action of piperonoyl chloride on piperidine.

Reactions
Piperine forms salts only with strong acids. The platinichloride B4·H2PtCl6 forms orange-red needles ("B" denotes one mole of the alkaloid base in this and the following formula). Iodine in potassium iodide added to an alcoholic solution of the base in the presence of a little hydrochloric acid gives a characteristic periodide, B2·HI·I2, crystallizing in steel-blue needles with melting point 145 °C.

Piperine can be hydrolyzed by an alkali into piperidine and piperic acid.

In light, especially ultraviolet light, piperine is changed into its isomers chavicine, isochavicine and isopiperine, which are tasteless.

History
Piperine was discovered in 1819 by Hans Christian Ørsted, who isolated it from the fruits of Piper nigrum, the source plant of both black and white pepper. Piperine was also found in Piper longum and Piper officinarum (Miq.) C. DC. (=Piper retrofractum Vahl), two species called "long pepper".