DNA polymerase β inhibitors from Tetracera boiviniana

Bioassay-guided fractionation of an active methyl ethyl ketone extract of Tetracera boiviniana, using a sensitive assay to monitor DNA. polymerase beta inhibition, resulted in the isolation of three known triterpenoids, betulinic acid (1), 3-cis-p-coumaroyl maslinic acid (2), and 3-trans-p-coumaroyl maslinic acid (3). Compounds 1-3 inhibited DNA polymerase beta with IC50 values of 14, 15, and 4.2 mu M in the presence of bovine serum albumin (BSA) and 6.5, 7.5, and 2.0 mu M in the absence of BSA, respectively. Further, compounds 1-3 potentiated the effects of bleomycin in cultured P-388D(1) cells.