The present invention relates to heterocyclic compounds represented by the formula I or pharmaceutically acceptable salts thereof and antitumor agents containing the heterocyclic compounds as effective components: ##STR00001## wherein X represents nitrogen atom or CH; R.sub.1 represents CH.sub.nF.sub.3-n (wherein n is 1 or 2), hydroxy C.sub.1-C.sub.6 alkyl, NHR.sub.6 [wherein R.sub.6 represents hydrogen atom or COR (wherein R represents hydrogen atom, C.sub.1-C.sub.6 alkyl or C.sub.1-C.sub.6 alkoxy)]; R.sub.2 represents morpholino (which may be substituted with one to four C.sub.1-C.sub.6 alkyl), thiomorpholino, piperidino, pyrrolidinyl (which may be substituted with hydroxy C.sub.1-C.sub.6 alkyl), oxazolidinyl (which may be substituted with one or two C.sub.1-C.sub.6 alkyl) or tetrahydro-1,4-thiazin-1-oxo-4-yl; R.sub.3 and R.sub.4 each represent hydrogen atom or C.sub.1-C.sub.6 alkyl; and R.sub.5 represents hydrogen atom, amino or hydroxyl.