New Galloylated Flavanonols from the Australian Plant Glochidion sumatranum

Abstract

Bioassay-guided fractionation of the CH₂Cl₂/MeOH extract from the Australian plant Glochidion sumatranum resulted in the isolation of four new galloylated flavanonols, (2R,3R)-dihydromyricetin-4′-O-(3′′-O-methyl)-gallate (1), (2R,3R)-dihydromyricetin-3′-O-(3′′-O-methyl)-gallate (2), (2R,3R)-dihydromyricetin-4′-O-gallate (3), and (2R,3R)-dihydromyricetin-3′-O-gallate (4), along with the known compound, (2R,3R)-dihydromyricetin (5). The structures of 1–5 were determined by NMR and MS analysis and their absolute configuration was elucidated by comparison of the CD data with literature values. Compounds 1/2 and 3/4 are two pairs of structural isomers that were shown to interconvert by transesterification during NMR and LC‐MS studies. This process involved the intramolecular migration of the galloyl moieties between C-3′ and C-4′ of the flavanonol skeleton. Compounds 1 and 3 were identified as the more stable isomers. Compounds 1, 3, and 5 showed weak activity against the gram-negative bacterium Pseudomonas aeruginosa and the gram-positive bacterium Staphylococcus aureus.

Key words

Glochidion sumatranum - Euphorbiaceae - galloylated flavanonols - structural isomer - antibacterial activity

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