Design of Reversible, Cysteine-Targeted Michael Acceptors Guided by Kinetic and Computational Analysis

Electrophilic probes
that covalently modify a cysteine thiol often
show enhanced pharmacological potency and selectivity. Although reversible
Michael acceptors have been reported, the structural requirements
for reversibility are poorly understood. Here, we report a novel class
of acrylonitrile-based Michael acceptors, activated by aryl or heteroaryl
electron-withdrawing groups. We demonstrate that thiol adducts of
these acrylonitriles undergo β-elimination at rates that span
more than 3 orders of magnitude. These rates correlate inversely with
the computed proton affinity of the corresponding carbanions, enabling
the intrinsic reversibility of the thiol-Michael reaction to be tuned
in a predictable manner. We apply these principles to the design of
new reversible covalent kinase inhibitors with improved properties.
A cocrystal structure of one such inhibitor reveals specific noncovalent
interactions between the 1,2,4-triazole activating group and the kinase.
Our experimental and computational study enables the design of new
Michael acceptors, expanding the palette of reversible, cysteine-targeted
electrophiles.