Microwave-Assisted Desulfonylation of Polysulfonamides toward Polypropylenimine

Linear polyethylenimine (L-PEI) has been the gold standard for gene delivery and is typically prepared by hydrolysis from poly(2-oxazoline)s. Recently, also the anionic polymerization of activated aziridines was reported as a potential pathway toward linear and well-defined polyamines. However, only sulfonamide-activated aziridines so far undergo the living anionic polymerization and their desulfonylation was only reported scarcely. This is mainly due to the relatively high stability of the sulfonamides and the drastic change in solubility during the desulfonylation. Herein, we investigated the desulfonylation of such poly(aziridine)s prepared from tosylated or mesylated propyleneimine to afford linear polypropylenimine (L-PPI) as an alternative to L-PEI. Different desulfonylation strategies for tosylated (Ts) and mesylated (Ms) PPI were studied. The reductive cleavage of the sulfonamide with sodium bis(2-methoxy ethoxy) aluminum hydride yielded 80% of deprotected amine groups. Quantitative conversion to L-PPI was obtained, when the tosylated PPI was hydrolyzed under acidic conditions with pTsOH under microwave (MW) irradiation. The same treatment removed 90% of the mesyl groups from the mesylated PPI analog. The MW-assisted acidic hydrolysis represents a fast, inexpensive and easy approach in comparison to other methods, where complex reaction conditions and tedious purifications are major drawbacks, however some chain scission may occur. The high purity of the obtained products, in combination with the versatility of the activated aziridine chemistry, demonstrate many advantages of our strategy, especially for future biomedical implementations.