Bioassay-guided fractionation of the EtOH extract of the bark of Uncario gu
ianensis (Aubl.) Gmel (Rubiaceae) using a yeast-based assay for DNA-damagin
g agents has furnished the two weakly but selectively active indole alkaloi
ds uncarine C (1) and uncarine E (2) as the major bioactive constituents in
this assay.