2.3.2.3 Scopoletin
Synonyms Chrysatropic acid; Gelseminic acid; 6-Methoxyumbelliferone; β-Methylesculetin; 7-Hydroxy 6-methoxycoumarin.
Biological Sources It is the aglucone of scopolin. Scopoletin occurs in the roots of Arnica montana L. (Asteraceae)-Mountain Tobacco, Leopard’s-bane; leaves of Artemesia abrotanum L. (Asteraceae)-Southernwood, Old Man; roots and leaves of Atropa belladona L. (Solanaceae)-Belladonna, Deadly Nightshade; barks of Brunfelsia uniflorus (Phol.) D. Don. (Solanaceae)-Manaca, Manacan; fruits of Capsicum annuum L. (Solanaceae)-Chili, Sweet Peppers, Paprika; oil of the plant Chamaemelum nobile (L.) All. (Asteraceae)-Roman Comomile; English Camomile, Comomile; and roots of Withania somniferum (L.) Dunal (Solanaceae)-Ashwagandha.
Preparation It is obtained by the hydrolysis of the glucoside scopolin i.e., 7-(β-D glucopyranosyloxy)-6-methoxy-2H-1-benzopyran-2-one as follows:
Characteristic Features Scopoletin occurs as prisms or needles from either acetic acid or chloroform. It melts at 204°C and has a uvmax: 230, 254, 260, 298, 346 nm (log ε 4.11, 3.68, 3.63, 3.68, 4.07). It is slightly soluble in water or cold ethanol and quite soluble in hot ethanol and hot glacial acetic acid. It is moderately soluble in chloroform, but practically insoluble in the non-polar solvent benzene.
Identification Tests
1. Dissolve 0.1 g in ethanol and warm it in an electric water-bath to affect dissolution. The resulting solution gives a blue fluorescence.
2. A solution of 0.1 g in 3 ml of hot ethanol reduces the Fehling’s solution thereby leaving behind a brick-red precipitate of cupric oxide (CuO).
It is pertinent to mention here that there exists some rarer species of hydroxycoumarins, such as: daphentin and fraxetin, which shall now be discussed in the sections that follows:
