A dihydroxyanthraquinone is any of several isomeric organic compounds with formula C
₁₄H
₈O
₄, formally derived from 9,10-anthraquinone by replacing two hydrogen atoms by hydroxyl groups. Dihyroxyantraquinones have been studied since the early 1900s, and include some compounds of historical and current importance.^[1][2] The isomers differ in the position of the hydroxyl groups, and of the carbonyl oxygens (=O) of the underlying anthraquinone.

Isomers

From 9,10-anthraquinone

The unqualified term "dihydroxyanthraquinone" usually means a hydroxy derivative of 9,10-anthraquinone. The dihydroxy-9,10-anthraquinone functional group occurs widely in natural products,^[3][4][5] and is an important feature of the anthracycline antitumour antibiotics.^[6][7] In particular, 1,8-Dihydroxy-9,10-anthraquinone is the precursor for the important topical antipsoriatic drug anthralin, 1,8-dihydroxy-9-anthrone,^[8][9]

There are 28 ways of choosing two of the 8 possible hydrogens, but because of the four-fold symmetry of the 9,10-anthraquinone core there are only 10 distinct isomers.^[10]

• 1,2-Dihydroxyanthraquinone (alizarin)
• 1,3-Dihydroxyanthraquinone (purpuroxanthin, xantopurpurin)
• 1,4-Dihydroxyanthraquinone (quinizarin)
• 1,5-Dihydroxyanthraquinone (anthrarufin)
• 1,6-Dihydroxyanthraquinone
• 1,7-Dihydroxyanthraquinone
• 1,8-Dihydroxyanthraquinone (dantron, chrysazin)
• 2,3-Dihydroxyanthraquinone (histazarin)
• 2,6-Dihydroxyanthraquinone (anthraflavic acid)
• 2,7-Dihydroxyanthraquinone (isoanthraflavic acid)

From other anthraquinones

There are also many dihydroxy derivatives of other anthraquinones, such as 1,2-anthraquinone, 1,4-anthraquinone, and 2,6-anthraquinone.^[10]