A new method for isolation of natural colourant, shikalkin from Arnebia nobilis Reichb.f. roots

Alkannin/shikonin (±)-5, 8-dihydroxy-2-(1-hydroxy-4-methyl-3-pentenyl)-1,4-naphthoquinone), also known as Shikalkin, is a racemic mixture of naturally occurring isohexenylnaphthazarin compounds. The (S) isomer is called as alkannin and (R) isomer is called as shikonin. Study was undertaken with an objective to develop a method for isolation of shikalkin from roots of Arnebia nobilis Reichb.f. by a rapid and efficient method. Roots of A. nobilis were cold macerated with chloroform and the extract was concentrated and subjected to alkaline hydrolysis. This extract was then acidified and extracted in light petroleum ether and purified using selective solvent extraction. The isolated compound was subjected to UV, FTIR, HNMR and Mass Spectroscopy studies for identification of chemical structure. Its purity was assessed by TLC and HPLC, and based on this data the compound isolated was ascertained to be shikalkin.