E. Piperine
Biological Source It is obtained from the dried unripe fruit of Piper nigrum L. (Black Pepper), Piper longum L., Piper retrofractum Vahl. (Piper officinarum C.D.C.), and Piper clusii C.D.C.; and also in the root bark of Piper geniculatum. Sw. belonging to family Piperaceae.
Chemical Structure
(E, E)-1-[5-(1, 3-Benzodioxol-5-yl)-1-oxo-2, 4-pentadienyl] piperidine (C17H19NO3).
Isolation The dried unripe fruits are extracted with ethanol in a Soxhlet apparatus till extraction is complete. The solvent is evaporated under vacuo in a Rotary Thin Film Evaporator. The residue of the alcoholic extract is digested with dilute alkali to affect saponification, when piperine remains unaffected. The residue, thus obtained is decanted and washed with distilled water several times.
The resulting product is dissolved in hot ethanol and on cooling the crystalline piperine separates out.
Characteristic Features
1. Piperine is obtained as monoclinic prisms from alcohol having mp 130°C.
2. It is tasteless at first, but has a burning aftertaste.
3. Its dissociation constant pK (18°C) is 12.22.
4. Solubility Profile: 1 g of piperine dissolves in 15 ml ethanol, 1.7 ml chloroform, 36 ml ether; freely soluble in acetic acid and benzene; and almost insoluble in water (40 mg/L at 18°C), and petroleum ether.
Identification Tests
1. Wagner’s Reagent Test: The addition of Wagner’s reagent to an alcoholic solution of piperine gives rise to bluish needle like crystals having mp 145°C.
2. Platinum Chloride Test [H2PtCl6]: Piperine on treatment with platinum chloride solution (0.5% w/v/) produces an instant orange red colouration, which upon standing gives needles of piperine-H2PtCl6.
3. Piperine reacts with a few drops of concentrated sulphuric acid yields a distinct red colouration.
Uses
1. It is used as an insecticide.
2. It is also employed extensively as condiment in food preparations.
3. It is used to give a ‘pungent’ taste to brandy.
Biosynthesis of Piperine In the biosynthesis of piperine, the piperidine ring forms part of a tertiary amide moiety which is incorporated via piperidine itself i.e., the reduction product of D1-piperideine as shown under. Interestingly, the piperic acid residue in obtained from a cinnamoyl-CoA precursor. The extension of chain is caused by virtue of acetate/malonate and ultimately combines as its CoA-ester with the previously obtained piperidine nucleus.
