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. (C) 1998 Elsevier Science Ltd. All rights reserved.