Programmable wide-range pH gradients for NMR titrations: application to antibody–drug conjugate linker group modifications

Abstract

We generate pH gradients spanning more than six units in standard NMR tubes and determine all the pK_a values of polyprotic compounds in single 20 minutes chemical shift imaging (CSI) NMR experiments. The modest demands of our method in terms of sample quantity and preparation time allow it be performed as part of the routine characterisation and optimisation of organic molecules during synthesis campaigns. As proof of concept, we measure the pK_a values of a family of vinylpyridines employed as antibody drug conjugate linkers. Our analysis reveals a strong correlation between the experimental aqueous pK_a and the rate of conjugate addition of thiol nucleophiles to the vinyl group, representing a powerful predictive method.