|Preferred IUPAC name
C.I. Natural red 20
3D model (JSmol)
|E number||E103 (colours)|
|Molar mass||288.299 g·mol−1|
|Appearance||Red-brown crystalline prisms|
|Melting point||149 °C (300 °F; 422 K)|
|Boiling point||567 °C (1,053 °F; 840 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|3.0 g/kg (mice)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
(what is ?)
Alkannin is a natural dye that is obtained from the extracts of plants from the borage family Alkanna tinctoria that are found in the south of France. The dye is used as a food colouring and in cosmetics. It is used as a red-brown food additive in regions such as Australia. Alkannin is deep red in an acid and blue in an alkaline environment. The chemical structure as a naphthoquinone derivative was first determined by Brockmann in 1936. The R-enantiomer of alkannin is known as shikonin, and the racemic mixture of the two is known as shikalkin.
The enzyme 4-hydroxybenzoate geranyltransferase utilises geranyl diphosphate and 4-hydroxybenzoate to produce 3-geranyl-4-hydroxybenzoate and diphosphate. These compounds are then used to form alkannin.
Because the root bark (cork layers) of this plant contains large amounts of red naphthoquinone pigments, the roots of these plants are red-purple. If shikonin is extracted from fresh tissues, it gradually darkens over several days, finally forming black precipitates, which are thought to be polymers.
- The Merck Index, 11th Edition, 243
- Additives Archived 2011-04-06 at the Wayback Machine, Food Standards Australia New Zealand
- "Alkanet" in Dispensatory of the United States of America, year 1918, edited by Joseph P. Remington and Horatio C. Wood.
- H. Brockmann (1936). "Die Konstitution des Alkannins, Shikonins und Alkannans". Justus Liebigs Ann. Chem. 521: 1–47. doi:10.1002/jlac.19365210102.
- Shmuel Yannai (2012). Dictionary of Food Compounds. CRC Press. p. 478.
- Vassilios P. Papageorgiou; Andreana N. Assimopoulou; Elias A. Couladouros; et al. (1999). "The Chemistry and Biology of Alkannin, Shikonin, and Related Naphthazarin Natural Products". Angew. Chem. Int. Ed. 38 (3): 270–300. doi:10.1002/(SICI)1521-3773(19990201)38:3<270::AID-ANIE270>3.0.CO;2-0.
- Kazufumi Y. (2017). Lithospermum erythrorhizon cell cultures: Present and future aspects. Plant Biotechnology 34: 131–142.