(S (S (S (VP (VP (VBG Comparing) (NP (BASENP (DT the) (NN impact)) (PP (IN of) (BASENP (NN parthenolide))))) (PP (TO to) (BASENP (DT the) (JJ common) (NN chemotherapy) (NN drug) (NN cytarabine))))) (COMMA ,) (S (BASENP (PRP they)) (VP (VBD found) (SBAR (IN that) (S (S (BASENP (NN parthenolide)) (VP (ADVP (RB selectively)) (VP (VBD killed) (BASENP (NN leukemia) (NNS cells))))) (SBAR (IN while) (S (VP (VP (VBG sparing) (BASENP (JJ normal) (NNS cells))) (ADVP (RBR better)))))))))) (PERIOD .))