First 2-hydroxy-3-methylbut-3-enyl substituted xanthones isolated from plants: structure elucidation, synthesis and antifungal activity.

Two new 2-hydroxy-3-methylbut-3-enyl substituted xanthones, (+/-)-caledol 1 and (+/-)-dicaledol 2 were isolated from a dichloromethane extract of the leaves of Calophyllum caledonicum (Clusiaceae). Compounds 1 and 2 are the first 2-hydroxy-3-methylbut-3-enyl substituted xanthones isolated from natural source. Their structures were elucidated by means of combined analytical methods including HRFABMS, 1D and 2D NMR spectroscopies and also confirmed by total synthesis using biomimetic ortho-prenylphenols photooxygenation (1O2) as a key step. The antifungal activity against Aspergillus fumigatus is reported.