Synthesis of Glycopeptide Antibiotic Peptide Substrates Using Knorr‐Pyrazole Chemistry

The glycopeptide antibiotics (GPAs) remain clinical antibiotics used against drug-resistant Gram-positive infections. The discovery of GPAs continues, with new type IIa and V GPAs, the kineomicins, the rimomycins, and corbomycin, being recently identified. Despite this larger repertoire of GPA scaffolds and crosslinking types, limitations remain with the in vitro exploration of the cytochrome P450 enzymes that install the essential crosslinks between the aromatic side chain residues of GPAs. While the chemoenzymatic synthesis of the more hydrophilic type I GPAs like vancomycin has aided our understanding of GPA crosslinking pathways, type II-V GPAs remain underexplored. This is due to the hydrophobic nature of these GPAs that makes access to peptidyl-CoA substrates difficult and reduces in vitro crosslinking activity. Here, we explore the use of modified Knorr-pyrazole chemistry to provide access to hydrophobic peptidyl-CoA substrates of the type II/IIa GPAs, kineomicin and actinoidin, and the type IV GPA, teicoplanin. Yields of peptidyl-CoAs were improved 3-7-fold through careful tuning of reaction solvents and the arylthiol used for displacement of the pyrazole. The type II/IIa GPA scaffolds explored in this study displayed the highest in vitro OxyC activity seen to date, likely due to both improved synthesis and their structural properties.