Abstract: A compound of the following formula (I) exhibits an excellent antitumor activity ##STR1## wherein R.sub.1 and R.sub.2 represent hydrogen atom, respectively, or include both straight or branch chain alkylidene group of 1-10 carbon atoms; R.sub.3 represents hydrogen atoms, straight and branch chain alkyl group of 1-10 carbon atoms, straight or branch chain alkyloxycarbonyl group of 1-10 carbon atoms or 3-membered to 6-membered heterocycle containing one nitrogen atom with adjacent alkylene group such as pyrrolidine and N-butoxycarbonyl-pyrrolidine; R.sub.4 and R.sub.5 represent hydrogen atom or alkyl group of 1-5 carbon atoms, respectively; and n represents 0 or an integer of 1-10, or pharmaceutically acceptable salt thereof.