A Cysteine-Directed Proximity-Driven Crosslinking Method for Native Peptide Bicyclization

Efficient and site-specific modification of native peptides and proteins is desirable for synthesizing antibody-drug conjugates as well as for constructing chemically modified peptide libraries using genetically encoded platforms such as phage display. In particular, there is much interest in efficient multicyclization of native peptides due to the appeals of multicyclic peptides as therapeutics. However, conventional approaches for multicyclic peptide synthesis require orthogonal protecting groups or non-proteinogenic clickable handles. Herein, we report a cysteine-directed proximity-driven strategy for the constructing bicyclic peptides from simple natural peptide precursors. This linear to bicycle transformation initiates with rapid cysteine labeling, which then triggers proximity-driven amine-selective cyclization. This bicyclization proceeds rapidly under physiologic conditions, yielding bicyclic peptides with a Cys-Lys-Cys, Lys-Cys-Lys or N-terminus-Cys-Cys stapling pattern. We demonstrate the utility and power of this strategy by constructing bicyclic peptides fused to proteins as well as to the M13 phage, paving the way to phage display of novel bicyclic peptide libraries.

New Three-Component Bicyclization Leading to Densely Functionalized Pyrazolo[3,4-d]thiazolo[3,2-a]pyrimidines

A novel three-component bicyclization for the efficient synthesis of densely functionalized pyrazolo[3,4-d]thiazolo[3,2-a]pyrimidines has been established from readily accessible aryl aldehydes, α-thiocyanate ketones and pyrazol-5-amines. The reaction pathway involves nucleophilic addition/5-exo-trig /6-endo-trig bicyclization sequence, resulting in continuous multiple bond-forming events including C-N and C-C bonds to rapidly a molecular complexity.