Dimeric xanthones from Garcinia livingstonei

From the root bark of Garcinia livingstonei , three xanthone dimers have been isolated. Structure elucidation was achieved mainly by NMR and mass spectrometry, including extensive NOE difference measurements, and by comparison with monomeric prenylated xanthones previously isolated from the same plant. Garcilivin A–C are structurally related to 1,4,5-trihydroxy-3-(3-methylbut-2-enyl)-9 H -xanthen-9-one and formally derive from the corresponding diene via dimerization by a Diels-Alder-type reaction.