Identification of 7,4prime-Dihydroxy-5-methoxyflavylium in ldquoDragon's Bloodrdquo: To Be or Not To Be an Anthocyanin

• Autor(a) principal: Melo, Maria J.
• Data de Publicação: 2007
• Outros Autores: Sousa, Micaela, Parola, A. Jorge, Melo, J. Sérgio Seixas de, Catarino, Fernando, Marçalo, Joaquim, Pina, Fernando
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10316/10111; https://doi.org/10.1002/chem.200600837

The compound 7,4prime-dihydroxy-5-methoxyflavylium (dracoflavylium) was identified as the major red colorant in samples of the resin ldquodragon's bloodrdquo, extracted from the tree Dracaena draco. The complex network of reversible chemical reactions that dracoflavylium undergoes in aqueous solution is fully described; for the first time, all the equilibrium constants that enable a complete characterisation of the system have been obtained (Kprimea=1.6×10-4, Ka1=1.0×10-4, Ka2=3.2×10-8, KCt1=1.0×10-7, KCt2=1.3×10-10). It is concluded that the red colour is due to a stable quinoid base, A, which is the major species at pH 4-7. It is further shown that this compound does not fit the commonly accepted definitions of anthocyanidin nor 3-deoxyanthocyanidin. Similarly to synthetic flavylium salts, the natural compound 7,4prime-dihydroxy-5-methoxyflavylium gives rise to several species (multistate system) reversibly interconverted by external stimuli, such as pH.