Quercetin, a flavonoid from fruits and leaves, acts like curcumin and piperine. Like "Piper nigrum", the fruits contain the alkaloid piperine, which contributes to their pungency. Besides the antibiotics rifampicin and isoniazid it contains piperine. Both men obtained piperidine by reacting piperine with nitric acid. In most cases, ginger acts synergistically with piperine. Piperine is extracted from black pepper by using dichloromethane. He discovered and synthesized the first lactones and investigated structures of piperine naphthalene and fluorene. These include piperine, which gives black pepper its spicy taste. Piperine yields salts only with strong acids. It is one of the four geometric isomers of piperine. Piperine remains the most potent and extensively researched bioenhancer till date.