Alkannin is a

natural dye Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources— roots, berries, bark, leaves, and wood—and other biological sources such as fungi. Ar ...

that is obtained from the extracts of plants from the

borage Borage ( or ; ''Borago officinalis''), also known as starflower, is an annual herb in the flowering plant family Boraginaceae. It is native to the Mediterranean region, and has naturalized in many other locales. It grows satisfactorily in gard ...

family ''

Alkanna tinctoria ''Alkanna tinctoria'', the dyer's alkanet or simply alkanet, is a herbaceous flowering plant in the borage family Boraginaceae. Its roots are used to produce a red dye. The plant is also known as dyers' bugloss, orchanet, Spanish bugloss, or La ...

'' that are found in the south of France. The dye is used as a

food colouring Food coloring, or color additive, is any dye, pigment, or substance that imparts color when it is added to food or drink. They come in many forms consisting of liquids, powders, gels, and pastes. Food coloring is used in both commercial food ...

and in cosmetics. It is used as a red-brown

food additive Food additives are substances added to food to preserve Taste, flavor or enhance taste, appearance, or other sensory qualities. Some additives have been used for centuries as part of an effort to preserve food, for example vinegar (pickling), sal ...

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 In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical anti ...

of alkannin is known as shikonin, and the

racemic mixture In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...

of the two is known as shikalkin.

Biosynthesis

The enzyme 4-hydroxybenzoate geranyltransferase utilises

geranyl diphosphate Geranyl pyrophosphate (GPP), also known as geranyl diphosphate (GDP), is the pyrophosphate ester of the terpenoid geraniol. Its salts are colorless. It is a precursor to many natural products. Occurrence GPP is an intermediate in the isoprenoid ...

and

4-hydroxybenzoate 4-Hydroxybenzoic acid, also known as ''p''-hydroxybenzoic acid (PHBA), is a monohydroxybenzoic acid, a phenolic derivative of benzoic acid. It is a white crystalline solid that is slightly soluble in water and chloroform but more soluble in polar ...

to produce 3-geranyl-4-hydroxybenzoate and diphosphate. These compounds are then used to form alkannin.

Research

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.Kazufumi Y. (2017). Lithospermum erythrorhizon cell cultures: Present and future aspects. Plant Biotechnology 34: 131–142.

References

External links

Shikonin at Sigma-Aldrich
Food colorings 1,4-Naphthoquinones Terpeno-phenolic compounds Articles containing video clips Hydroxynaphthoquinones Secondary alcohols 3-Hydroxypropenals within hydroxyquinones Alkene derivatives