Sulfonyl fluorides have recently been described as “privileged warheads” in chemical biology due to the right balance of reactivity and stability that these electrophiles possess. Peptido sulfonyl fluorides (β-PSFs) have shown to be particularly potent as proteasome inhibitors in recent years. Tuning the reactivity of the sulfonyl fluoride electrophilic trap may be crucial for modulating its
biological action.
The first part of this thesis describes the design and synthesis of peptido sulfonyl fluoride derivatives containing a substituent on the alpha position with respect to the sulfonyl fluoride electrophilic trap. Therefore, the chemical reactivity and biological activity of α-substituted sulfonyl fluorides (αSFs) were studied. Comparison with the previously described β-substituted sulfonyl fluorides (βSFs) was performed as an attempt to get a deeper insight into the importance of the immediate structural environment of the sulfonyl fluoride moiety. αSFs proved to be more reactive than βSFs towards nucleophilic substitution, including hydrolysis.
However, it could not be clarified as yet if and how this is translated to the bioactivity of the resulting α-PSFs since the poor solubility of these molecules precluded a proper evaluation.
The second part of this thesis describes the synthesis of a vinyl sulfonyl fluoride moiety as a new dual warhead class. The consecutive attack of the two nucleophiles of the proteasome active threonine on the double bond and the sulfonyl fluoride was proposed as the inhibition mechanism which should lead to the formation of a seven-membered covalent adduct. In vitro studies were designed in order to test this hypothesis. Although the formation of the proposed
seven-membered ring structure could not be unambiguously demonstrated with the chosen model systems, the crystal structure confirmed this formation within enzymatic environment. Incorporation of vinyl sulfonyl fluoride warhead into peptide backbones (PVSF) resulted in strong proteasome inhibitors (IC50 = 99 and 218 nM)
