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, berry, berries, Bark (botany), bark, leaf, leaves, and wood—and other biological sourc ...

that is obtained from the extracts of the plant dyer's alkanet (''Alkanna tinctoria'') which is found in the Mediterranean region. The dye is used as a

food coloring Food coloring, color additive or colorant is any dye, pigment, or substance that imparts color when it is added to food or beverages. Colorants can be supplied as liquids, powders, gels, or pastes. Food coloring is commonly used in commercia ...

and in cosmetics; within the European

E number E numbers, short for Europe numbers, are codes for substances used as food additives, including those found naturally in many foods, such as vitamin C, for use within the European Union (EU) and European Free Trade Association (EFTA). Commonly ...

schedule, it is numbered E103. It is used as a red-brown

food additive Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives, such as vinegar ( pickling), salt ( salting), smoke ( smoking) and sugar ( crystallization), have been used f ...

in regions such as Australia. Alkannin is deep red in an acid and blue in an alkaline environment. The chemical structure as a

naphthoquinone Naphthoquinones constitute a class of organic compounds structurally related to naphthalene. Two isomers are common for the parent naphthoquinones: * 1,2-Naphthoquinone * 1,4-Naphthoquinone Natural products * Alkannin * Hexahydroxy-1,4-nap ...

derivative was first determined by Hans Brockmann in 1936. The (''R'')-

enantiomer In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

of alkannin is known as shikonin, and the

racemic mixture In chemistry, a racemic mixture or racemate () is a mixture that has equal amounts (50:50) 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 r ...

of the two is known as shikalkin.

Biosynthesis

The enzyme 4-hydroxybenzoate geranyltransferase utilizes

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 thousands of natural products. Occurrence GPP is an intermediate in the ...

and

4-hydroxybenzoic acid 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-hydroxybenzoic acid and diphosphate. These compounds are then used to form alkannin.

Research

Because the root bark (cork layers) of ''Alkanna tinctoria'' contains large amounts of red

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.

References

{{reflist Food colorings 1,4-Naphthoquinones Terpeno-phenolic compounds Articles containing video clips Hydroxynaphthoquinones Secondary alcohols 3-Hydroxypropenals within hydroxyquinones Alkene derivatives