Because conjugation selectivity as well as stability and hydrophobicity of linkers and payloads drastically influence the performance and safety profile antibody-drug conjugates, the requirements for novel bioconjugation reactions for the synthesis of ADCs are exceptionally high.
In a new article, published in the international edition of Angewandte Chemie, a journal of the German Chemical Society, Marc-André Kasper, Andreas Stengl, Philipp Ochtrop and colleagues describe Cys‐selective ethynylphosphonamidates as new reagents for the rapid generation of efficacious ADCs from native non‐engineered monoclonal antibodies, applying a simple one‐pot reduction and alkylation protocol.
According to the authors of the article, ethynylphosphonamidates can be easily substituted with hydrophilic residues, giving rise to electrophilic labeling reagents with tunable solubility properties. They demonstrate that ethynylphosphonamidate‐linked ADCs have excellent properties for next generation antibody therapeutics in terms of serum stability and in vivo antitumor activity.
Earlier this year the same researchers published an article in Angewandte Chemie describing a new technique in protein synthesis that extends the existing repertoire of methods for protein modification.
The technique includes a chemoselective reaction that induces reactivity for a subsequent bioconjugation. In this process, an azide‐modified building block reacts first with an ethynylphosphonite through a Staudinger‐phosphonite reaction (SPhR) to give an ethynylphosphonamidate. The resulting electron‐deficient triple bond subsequently undergoes a cysteine‐selective reaction with proteins or antibodies. The scientists demonstrated that ethynylphosphonamidates displays excellent cysteine‐selective reactivity combined with superior stability of the thiol adducts, when compared to classical maleimide linkages. This turns our technique into a versatile and powerful tool for the facile construction of stable functional protein conjugates.
 Kasper MA, Stengl A, Ochtrop P, Gerlach M, Stoschek T, Schumacher D, Helma J, et al. Ethynylphosphonamidates for the rapid and cysteine selective generation of efficacious Antibody-Drug-Conjugates. Angew Chem Int Ed Engl.2019 Jun 28. doi: 10.1002/anie.201904193. [Article]
 Kasper MA, Glanz M, Stengl A, Penkert M, Klenk S, Sauer T, Schumacher D, et al. Cysteine-Selective Phosphonamidate Electrophiles for Modular Protein Bioconjugations. Angew Chem Int Ed Engl. 2019 Mar 4. doi: 10.1002/anie.201814715. [Article]