Further rearranged prenylxanthones and benzophenones from Garcinia bracteata

New rearranged polyprenylxanthones, namely garcibracteatone, neoisobractatins A and B, and xerophenone C were isolated from the leaves and bark of a vietnamese Garcinia, Garcinia bracteata, together with 5-O-methylxanthone V1, bracteaxanthones I and II, and the known nemorosonol and simple xanthones. Neoisobractatins A and B exhibit a significant cytotoxic activity on KB cells. A biogenetic hypothesis is proposed, which explains the possible origin of these so-called cage-xanthanoids.