141111-35-5Relevant articles and documents
Synthesis of carminic acid, the colourant principle of cochineal
Allevi, Pietro,Anastasia, Mario,Bingham, Steve,Ciuffreda, Pierangela,Fiecchi, Alberto,Cighetti, Giuliana,Muir, Max,Scala, Antonio,Tyman, John
, p. 575 - 582 (2007/10/03)
The first synthesis of carminic acid (7β-D-glucopyranosyl-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-9,10- dihydroanthracene-2-carboxylic acid) is described. Selective C-glycosylation at the 7-position of ethyl and benzyl 3,5,8,9,10-pentamethoxy-1-methylanthracene-2-carboxylates with 2,3,4,6-tetra-O-benzyl-1-trifluoroacetyl-α-D-glucopyranose afforded intermediates which were oxidised to ethyl and benzyl 3,5,8-trimethoxy-1-methyl-9,10-dioxo-7-(2′,3′,4′,6′- tetra-O-benzyl-β-D-glucopyranosyl)-9,10-dihydroanthracene-2-carboxylate respectively. The benzyl compound was hydrogenolysed and the ethyl analogue hydrogenolysed and hydrolysed to give the same product, which was tetraacetylated and demethylated to afford 6-deoxycarminic acid tetraacetate, 3,5,8-trihydroxy-1-methyl-9,10-dioxo-7-(2′,3′,4′,6′- tetra-O-acetyl-β-D-glucopyranosyl)-9,10-dihydroanthracene-2-carboxylic acid. The pentamethoxy intermediates were obtained from 2-chloronaphthazarin by Diels-Alder addition to 3-alkoxycarbonyl-2,4-bis(trimethylsiloxy)penta-2,4-dienes to give alkyl 6-deoxykermesates. Methylation afforded the corresponding trimethyl ethers, which by reductive methylation gave the required pentamethoxy compounds. By known steps 6-deoxycarminic acid tetraacetate was converted into the 5,8,9,10-bisquinone, acetoxylation of which gave carminic acid octaacetate. Acidic hydrolysis afforded carminic acid.
