Identification of 7,4'-dihydroxy-5-methoxyflavylium in "Dragon's blood": to be or not to be an anthocyanin.
The compound 7,4'-dihydroxy-5-methoxyflavylium (dracoflavylium) was identified as the major red colorant in samples of the resin "dragon's blood", 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 (K'(a)=1.6 x 10(-4), K(a1)=1.0 x 10(-4), K(a2)=3.2 x 10(-8), K(Ct1)=1.0 x 10(-7), K(Ct2)=1.3 x 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 7,4'-dihydroxy-5-methoxyflavylium gives rise to several species (multistate system) reversibly interconverted by external stimuli, such as pH.
Melo
Maria J
MJ
REQUIMTE-CQFB, Chemistry Department, Faculty of Sciences and Technology of the New University Lisbon, Campus da Caparica, Portugal. mjm@dq.fct.unl.pt
Sousa
Micaela
M
Parola
A Jorge
AJ
de Melo
J Sérgio Seixas
JS
Catarino
Fernando
F
Marçalo
Joaquim
J
Pina
Fernando
F
D000872:Anthocyanins / Q000737:chemistry*; D001578:Benzopyrans / Q000737:chemistry* / Q000302:isolation & purification; D029802:Croton / Q000737:chemistry*; D031409:Dracaena / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010936:Plant Extracts / Q000737:chemistry* / Q000302:isolation & purification; D010946:Plants, Medicinal / Q000737:chemistry*; D011809:Quinones / Q000737:chemistry; D013057:Spectrum Analysis; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry
C520075:7,4'-dihydroxy-5-methoxyflavylium; D000872:Anthocyanins; D001578:Benzopyrans; D010936:Plant Extracts; D011809:Quinones; D014867:Water