Their screening for their inhibitory activity onto carbonic anhydrase II and screening for their cytotoxicity in SRB assays employing several human tumor cell lines and non-malignant fibroblasts showed the conjugates derived from betulin and glycyrrhetinic acid to be the best inhibitors while those derived from ursolic or oleanolic acid were significantly weaker inhibitors but also of diminished cytotoxicity. This evidence concerns the gene CA2 and neoplasm.