Three-Component Protein Modification Using Mercaptobenzaldehyde Derivatives.

A chemoselective primary amine modification strategy that enables the three-component, one-pot bioconjugation is described. The specifically designed, mercaptobenzaldehyde-based bifunctional linker achieves highly selective and robust amine labeling under biocompatible conditions. This linker demonstrates wide functional group tolerance and is simple to prepare, which allowed facile payload incorporation. Finally, our studies have shown that the introduction of linker does not impair the function of modified protein such as insulin.

Coupling of sterically demanding peptides by ß-thiolactone-mediated native chemical ligation.

The ligation of sterically demanding peptidyl sites such as those involving Val-Val and Val-Pro linkages has proven to be extremely challenging with conventional NCL methods that rely on exogenous thiol additives. Herein, we report an efficient ß-thiolactone-mediated additive-free NCL protocol that enables the establishment of these connections in good yield. The rapid NCL was followed by in situ desulfurization. Reaction rates between ß-thiolactones and conventional thioesters towards NCL were also investigated, and direct aminolysis was ruled out as a possible pathway. Finally, the potent cytotoxic cyclic-peptide axinastatin 1 has been prepared using the developed methodology.