Potential prodrugs of the highly insoluble, diimide antitumor agent mitindomide (1b) were synthesized by several different methods. The condensation reaction between mitindomide and formaldehyde cleanly gave the stable bis(hydroxymethyl) compound 7a, which was partially soluble in water (ca. 0.8%) and showed improved activity in the P-388 screen. When this compound was treated with secondary amines, good yields of Mannich bases could be isolated. The compound from N-methylpiperazine (7b) had excellent properties and is a candidate for clinical trials. Condensation with other aldehydes gave either no reaction or compounds with poor activity. A water-soluble ester was prepared from 7a and succinic anhydride, but had reduced potency and activity. Oxidation of the double bond of 1a with ozone gave an inactive diacid, whereas the dihydro compound was as active as the olefin. When other aromatics (anisole, p-xylene, mesitylene) were photolyzed with maleimide, the resulting photoproducts were found to be inactive. Diimides from other ring system were synthesized from the corresponding anhydrides and found to be inactive. However, the bis(hydroxymethyl) derivative of one of these (12a) was active in the P-388 screen.