Methylation of dihydroquercetin acetates: synthesis of 5-O-methyldihydroquercetin.
The major products of methylation of dihydroquercetin (1, dhq) with diazomethane have been identified as 7-O-methyldhq (9), 7,3'-di-O-methyldhq (10), 7,4'-di-O-methyldhq (11), and 7,3',4'-tri-O-methyldhq (2). With dhq 3,7,3',4'-tetraacetate (6), dhq 3,5,3',4'-tetraacetate (5), dhq 3,3',4'-triacetate (7), dhq 7,3',4'-triacetate (8), and dhq 3-acetate (4) the same reaction affords mainly 5-O-methyldhq 3,7,3',4'-tetraacetate (15), 7-O-methyldhq 3,5,3',4'-tetraacetate (13), 7-O-methyldhq 3,3',4'-triacetate (14), 5-O-methyldhq 7,3',4'-triacetate (25), and 7-O-methyldhq 3-acetate (12), respectively. The methylation of 8 is accompanied by intermolecular acetyl migration from phenolic oxygen to the hydroxy group of the heterocyclic ring. 5-O-Methyldhq (28) is accessible by deacetylation of 25. 5,7-Di-O-methyldhq (29), four known methyl ethers, 13 new and three known methyl ether acetates of dhq, and six new isomers with 2,3-cis stereochemistry were spectroscopically identified.
Kiehlmann
Eberhard
E
Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6. ekie@sfu.ca
Slade
Peter W
PW
D000085:Acetates; D044948:Flavonols / Q000737:chemistry*; D007202:Indicators and Reagents; D008745:Methylation; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D011794:Quercetin / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
C482763:5-O-methyldihydroquercetin; D000085:Acetates; D044948:Flavonols; D007202:Indicators and Reagents; D011794:Quercetin; C003377:taxifolin