An efficient synthesis of dialkylsubstituted maleic anhydrides 1a–j is described. The inhibitory potential of these original anhydride derivatives was tested toward the three human isoforms A, B and C of dual specific phosphatases Cdc25. A micromolar range inhibition of Cdc25s was observed with the maleic anhydrides bearing simple alkyl side chains longer than C9, to reach the optimal activity with a C17 chain length.