Substances WB2663A, WB2663B and WB2663C are produced by culturing a WB2663-producing bacterium belonging to the genus Pseudomonas to form physiologically active substances and isolating therefrom neutral substances respectively having the following specific rotation: [ alpha ]<2><3> = -36 DEG (C =0.5 in CH2Cl2),[ alpha ]<2><3> = -12 DEG (C =0.5 in CH2Cl2), and [ alpha ]<2><3> = -9 DEG (C =0.5 in CH2Cl2). They have each an excellent antitumor activity.
