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 β 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 β with IC₅₀ values of 14, 15, and 4.2 μM in the presence of bovine serum albumin (BSA) and 6.5, 7.5, and 2.0 μM in the absence of BSA, respectively. Further, compounds 1-3 potentiated the effects of bleomycin in cultured P-388D₁ cells.