PHOTOCHEMICAL DECOMPOSITION OF ALKANNIN SHIKONIN ENANTIOMERS

Alkannin/shikonin ((+/-)-5,8-dihydroxy-2-(1-hydroxy-4-methyl-3-pentneyl)-1,4-napthoquinone), isolated from Macrotomia euchroma, is sensitive to light exposure. A chloroform solution of alkannin/shikonin was exposed to sunlight for 1 month. The major photolytic product, a newly discovered naphthoquinone derivative, was isolated by adsorption chromatography. The chemical structure of the purified photolytic product was identified by NMR, MS and FTIR techniques to be (-)-5,8-dihydroxy-2-(1-hydroxy-3-oxo-4-methyl-4-pentenyl)- 1,4-naphthoquinone, indicating that a photo-oxidation reaction had occurred.