# Substitution-Induced Mechanistic Switching in SNAr-Warheads for Cysteine Proteases

## TL;DR

This study explores how small structural changes in a compound can switch its mode of action from reversible to irreversible inhibition of a specific enzyme.

## Contribution

The study reveals how substitution patterns on a warhead scaffold can control the inhibition mechanism of cysteine proteases.

## Key findings

- Structure–activity relationships show how arene substitution affects inhibition potency and covalency.
- Molecular docking and quantum-mechanical calculations support the observed mechanistic transitions.
- Peptide esters show better membrane permeability than carboxylic acids.

## Abstract

The aim of this study was to investigate the transition from non-covalent reversible over covalent reversible to covalent irreversible inhibition of cysteine proteases by making delicate structural changes to the warhead scaffold. To this end, dipeptidic rhodesain inhibitors with different N-terminal electrophilic arenes as warheads relying on the SNAr mechanism were synthesized and investigated. Strong structure–activity relationships of the inhibition potency, the degree of covalency, and the reversibility of binding on the arene substitution pattern were found. The studies were complemented and substantiated by molecular docking and quantum-mechanical calculations of model systems. Furthermore, the improvement in the membrane permeability of peptide esters in comparison to their corresponding carboxylic acids was exemplified.