Rhomboid intramembrane proteases represent a subclass of serine hydrolases with membrane-embedded active sites. These proteins participate in critical cellular processes, such as mitochondrial quality control and growth factor signaling, though their physiological functions are still not fully understood. In addition, their abnormal activity has been linked to several diseases, including multiple types of cancer. Small-molecule competitive inhibitors have served as important chemical tools for studying and characterizing proteins. These inhibitors can be utilized to selectively target proteins of interest to investigate their activity in biological systems and provide insight into potential strategies for treating diseases. This work presents the divergent synthesis and testing of N-methylene-substituted saccharin-based structures as small-molecule, mechanism-based inhibitors for rhomboid intramembrane proteases. The synthetic route involves a three-step sequence to convert simple halo-substituted o-toluenesulfonyl chlorides into C3-C6 halo-substituted saccharins. After N-acyloxymethylation of these saccharins, Suzuki-Miyaura and Sonogashira cross-coupling reactions provide access to a range of alkyl, alkynyl, and aryl substituents in the C3-C6 positions. The influence of these different substituents on the inhibition of rhomboid proteases has been investigated using a competitive activity-based protein profiling (ABPP) strategy. Testing of the N-methylene-substituted saccharin-based inhibitors against PARL and RHBDL4, two human rhomboid proteases, has revealed that selective inhibition is possible. Continued development of these structures may enable the discovery of potent and selective rhomboid protease inhibitors in the future.

Synthetic route to access <i>N</i>-methylene-substituted saccharin-based inhibitors

Synthetic route to access N-methylene-substituted saccharin-based inhibitors

William Parsons

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