We first synthesized a-mangostin derivatives through various
modifications of the phenols at the C1, C3 and C6 positions
(Scheme 1). For the synthesis of acetates 4a and 4b, a-mangostin
was treated with acetic anhydride, Et3N and DMAP in CH2Cl2.13c
The carboxyl groups of 5a and 5b were introduced utilizing
methyl bromoacetate and K2CO3, followed by basic hydrolysis. As
predicted from the precedent examples of selective alkylation on
C-6 position prior to C-3, the allyl aryl ethers 6a and 6b were
obtained by treating 1 with allyl bromide and K2CO3.13a,14
Similarly, the triflates 7a and 7b were also prepared by trifluoromethanesulfonic
anhydride, Et3N and DMAP. The allyl group of
6a and 6b was used as a protecting group, while the triflates