An 8-hydroxylated external flavone and its 8-O-glucoside from Becium grandiflorum

The major vacuolar flavonoid of a greenhouse-grown plant of Becium grandiflorum has been identified as the 8-O-glucoside of isothymusin (5,8,4'-trihydroxy-6,7-dimethoxyflavone), while the major external flavonoids in the diethyl ether surface wash of the same plant are found to be isothymusin and cirsimaritin (5,4'-dihydroxy-7,8-dimethoxyflavone). Although isothymusin is already known as a conversion product of thymusin (5,6,4'-trihydroxy-6,7-dimethoxyflavone) formed by means of the Wessely-Moser rearrangement, this is the first report of isothymusin as a plant constituent, both as aglycone and glycoside. The biogenetic and chemotaxonomic implications of the occurrence of these flavonoids in B.grandiflorum are briefly discussed.