Predictive modeling and understanding of chemical warhead
reactivities
have the potential to accelerate targeted covalent drug discovery.
Recently, the carbanion formation free energies as well as other ground-state
electronic properties from density functional theory (DFT) calculations
have been proposed as predictors of glutathione reactivities of Michael
acceptors; however, no clear consensus exists. By profiling the thiol-Michael
reactions of a diverse set of singly- and doubly-activated olefins,
including several model warheads related to afatinib, here we reexamined
the question of whether low-cost electronic properties can be used
as predictors of reaction barriers. The electronic properties related
to the carbanion intermediate were found to be strong predictors,
e.g., the change in the Cβ charge accompanying carbanion
formation. The least expensive reactant-only properties, the electrophilicity
index, and the Cβ charge also show strong rank correlations,
suggesting their utility as quantum descriptors. A second objective
of the work is to clarify the effect of the β-dimethylaminomethyl
(DMAM) substitution, which is incorporated in the warheads of several
FDA-approved covalent drugs. Our data suggest that the β-DMAM
substitution is cationic at neutral pH in solution and promotes acrylamide’s
intrinsic reactivity by enhancing the charge accumulation at Cα upon carbanion formation. In contrast, the inductive
effect of the β-trimethylaminomethyl substitution is diminished
due to steric hindrance. Together, these results reconcile the current
views of the intrinsic reactivities of acrylamides and contribute
to large-scale predictive modeling and an understanding of the structure–activity
relationships of Michael acceptors for rational TCI design.