Further prenylated flavonols from Platanus acerifolia’s unripe buds

The toluene extract of defatted Platanus acerifolia’s fresh unripe buds afforded 8 metabolites. In all, prenylated flavonols 3–6 are reported for the first time in the plant kingdom. •The n-hexane extract of Platanus acerifolia’s unripe buds afforded 8 metabolites.•A total of 4 prenylated flavonols, unknown in the plant kingdom, corresponded to either galangin or kaempferide, substituted by an open or a cyclized C5 chain.•In all, 6 significant 13C NMR chemical shift variations are discussed when going from the open C5 side chain to the cyclized chain isomers. In addition to the methylated and prenylated flavonoids previously reported from Platanus acerifolia, the multistep chromatographic processing of the toluene extract of defatted fresh unripe buds resulted in the isolation of 8 metabolites. They corresponded to 5,7-dihydroxychromone, strobopinin [(2S)-5,7-dihydroxy-6-C-methylflavanone] as well as to six prenylated flavonols. Divided into two groups of three isomers, these C5-substituted flavonols are derived from either galangin (5,7-dihydroxyflavonol) or kaempferide (5,7-dihydroxy-4′-methoxyflavonol). Four of them, unknown in the plant kingdom and with either open or cyclized C5 chain, are discussed for the 13C NMR chemical shift variations when going from the open side C5 chain to the cyclized chain isomers.