Synthesis and evaluation of 4-(α-arylvinyl)pyridines as activated linker groups for application in antibody-drug...

With the aim of increasing the cysteine-selective bioconjugation reactivity of 4-vinylpyridines, a series of 4-(α-arylvinyl)pyridines were synthesised by Suzuki-Miyaura cross-coupling of 4-(α-bromovinyl)pyridine. The rate of thia-Michael addition of cysteine-containing glutathione correlated with σ_x of the aryl substituent (ρ = +0.94). Introduction of electron-donating and electron-withdrawing substituents at the 3-position of 2,6-dimethyl-4-vinylpyridine all resulted in a reduction in the rate of glutathione bioconjugation, and a shift from the optimum pK_a value of approximately 6-7 with the pK_a values determined by pH gradient NMR titration. Potential 'dual-armed' 2,6-disubstituted-4-vinylpyridine antibody-drug linker groups developed previously were modified by the α-vinyl arylation methodology. This resulted in an increase in the rate of glutathione bioconjugation of approximately an order of magnitude for the p-nitrophenyl derivatives, providing opportunities for the development of new antibody-drug conjugates.