The sulfonic esters of N-oxyimidesare a group of compounds with a wide range of biologicalactivities, as well as a unique reactivity towards amines. They undergo this reaction withprimary amines and other nucleophilic reagents according to a Lossen-like rearrangement. Thereaction is initiated by nucleophilic attack on a carbonyl group in the succinimide ring followedby isocyanate formation, which next interacts with another nucleophile molecule forming anaddition product (e.g., ureido or urethane derivative). However, the secondary amines are alsosusceptible to other reactions leading to products containing the maleimide ring formed bysulphonic acid elimination. In the case of tertiary amines, this reaction is predominant. Toexplain the phenomenon of the reactivity of the N-oxyimides towards different types ofamines, we employed various spectroscopic and X-ray approaches as well as DFT calculation.Results suggest that the basicity of the amine used for the reaction plays a crucial role in thereaction mechanism that eventually dominates the entire chemical process. Moreover, weapplied molecular docking to investigate the ability of the products to act as serine proteaseinhibitors using human leukocyte elastase (HLE).