Di-ester prodrugs of camptothecin, process for their preparation and their therapeutical applications

A di-ester compound having the following structure:

• wherein
• R1, R2, R3, and R4, which can be the same or different, are hydrogen, halogen, C1-C20 alkyl, C1-C8 alkoxyl, C4-C20 aryl or C1-C20 silyl,
• R, which can be the same or different, is C2-C30 alkyl, C2-C22 alkenyl, C4-C30 aryl, (CH2)nOR5, (CH2)nSR5, (CH2)nNR5R6 or (CH2)nCOR7,
• R5 and R6, which can be the same or different, are C1-C8 alkyl or C2-C6 alkenyl,
• R7 is hydroxy, C1-C20 alkyl, C1-C6 alkenyl, C1-C6 alkoxy, C4-C20 aryl, or NR8R9,
• R8 and R9, which can be the same or different, are C1-C6 alkyl,
• and n is an integer of 1 to 8,
• or a pharmaceutically acceptable salt thereof.