Alkannin is anatural dye that is obtained from the extracts of the plantdyer's alkanet (Alkanna tinctoria) which is found in theMediterranean region. The dye is used as afood coloring and in cosmetics; within the EuropeanE number schedule, it is numberedE103. It is used as a red-brownfood additive in regions such as Australia.[2] Alkannin is deep red in an acid and blue in an alkaline environment.[3] The chemical structure as anaphthoquinone derivative was first determined by Hans Brockmann in 1936.[4] The (R)-enantiomer of alkannin is known asshikonin, and theracemic mixture of the two is known asshikalkin.[5][6]
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| Names | |
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| Preferred IUPAC name 5,8-Dihydroxy-2-[(1S)-1-hydroxy-4-methylpent-3-en-1-yl]naphthalene-1,4-dione | |
Other names
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| Identifiers | |
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3D model (JSmol) | |
| ChEMBL | |
| ChemSpider |
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| ECHA InfoCard | 100.007.497 |
| E number | E103(colours) |
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| Properties[1] | |
| C16H16O5 | |
| Molar mass | 288.299 g·mol−1 |
| Appearance | Red-brown crystalline prisms |
| Density | 1.15 g/mL |
| Melting point | 149 °C (300 °F; 422 K) |
| Boiling point | 567 °C (1,053 °F; 840 K) |
| Sparingly soluble | |
| Hazards | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 3.0 g/kg (mice) |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Biosynthesis
editThe enzyme4-hydroxybenzoate geranyltransferase utilizesgeranyl diphosphate and4-hydroxybenzoic acid to produce3-geranyl-4-hydroxybenzoic acid and diphosphate. These compounds are then used to form alkannin.[6]
Research
editBecause the root bark (cork layers) ofAlkanna tinctoria contains large amounts of rednaphthoquinone pigments, including alkannin, the roots of these plants are red-purple. When extracted from fresh tissues, the pigment gradually darkens over several days, finally forming black precipitates, which are thought to be polymers.[7]
References
edit- ^The Merck Index, 11th Edition,243
- ^AdditivesArchived 2011-04-06 at theWayback Machine,Food Standards Australia New Zealand
- ^Joseph P. Remington and Horatio C. Wood, ed. (1918). "Alkanet".Dispensatory of the United States of America.
- ^H. Brockmann (1936). "Die Konstitution des Alkannins, Shikonins und Alkannans".Justus Liebigs Ann. Chem.521 (1):1–47.doi:10.1002/jlac.19365210102.
- ^Shmuel Yannai (2012).Dictionary of Food Compounds. CRC Press. p. 478.
- ^abVassilios 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.PMID 29711637.
- ^Yazaki, Kazufumi (2017)."Lithospermum erythrorhizon cell cultures: Present and future aspects".Plant Biotechnology.34 (3):131–142.doi:10.5511/plantbiotechnology.17.0823a.PMC 6565996.PMID 31275019.