Opening or closing the lock? when reactivity is the key to biological activity

Article abstract of DOI:10.1002/chem.201302117

Thiol-mediated processes play a key role to induce or inhibit inflammation proteins. Tailoring the reactivity of electrophiles can enhance the selectivity to address only certain surface cysteines. Fourteen 2',3,4,4'- tetramethoxychalcones with different α-X substituents (X=H, F, Cl, Br, I, CN, Me, p-NO₂-C₆H₄, Ph, p-OMe-C ₆H₄, NO₂, CF₃, COOEt, COOH) were synthesized, containing the potentially electrophilic α,β-unsaturated carbonyl unit. The assessment of their reactivity as electrophiles in thia-Michael additions with cysteamine shows a change in the reactivity of more than six orders of magnitude. Moreover, a clear correlation between their reactivity and an influence on the inflammation proteins heme oxygenase-1 (HO-1) and the inducible NO synthase (iNOS) is demonstrated. As the biologically most active compound, the α-CF₃-chalcone is shown to inhibit the NO production in RAW264.7 mouse macrophages in the nanomolar range. More than a million by only one substituent: The direct manipulation of the chemical reactivity of electrophilic agents could be proven for chalcones by simply exchanging the α-hydrogen atom of the α,β-unsaturated carbonyl unit with different substituents (X), leading to a change in reactivity of more than six orders of magnitude for thia-Michael additions with cysteamine, which correlates very well with two electrophile-sensitive biological readouts (see scheme).