Facile Synthetic Access to Glycopeptide Antibiotic Precursor Peptides for the Investigation of Cytochrome P450 Action in Glycopeptide Antibiotic Biosynthesis

The glycopeptide antibiotics are an important class of complex, medically relevant peptide natural products. Given that the production of such compounds all stems from in vivo biosynthesis, understanding the mechanisms of the natural assembly system--consisting of a nonribosomal-peptide synthetase machinery (NRPS) and further modifying enzymes--is vital. In order to address the later steps of peptide biosynthesis, which are catalyzed by Cytochrome P450s that interact with the peptide-producing nonribosomal peptide synthetase, peptide substrates are required: these peptides must also be in a form that can be conjugated to carrier protein domains of the nonribosomal peptide synthetase machinery. Here, we describe a practical and effective route for the solid phase synthesis of glycopeptide antibiotic precursor peptides as their Coenzyme A (CoA) conjugates to allow enzymatic conjugation to carrier protein domains. This route utilizes Fmoc-chemistry suppressing epimerization of racemization-prone aryl glycine derivatives and affords high yields and excellent purities, requiring only a single step of simple solid phase extraction for chromatographic purification. With this, comprehensive investigations of interactions between various NRPS-bound substrates and Cytochrome P450s are enabled.

Rapid access to glycopeptide antibiotic precursor peptides coupled with cytochrome P450-mediated catalysis: towards a biomimetic synthesis of glycopeptide antibiotics

Understanding the mechanisms underpinning glycopeptide antibiotic biosynthesis is key to the future ability to reinvent these compounds. For effective in vitro characterization of the crucial later steps of the biosynthesis, facile access to a wide range of substrate peptides as their Coenzyme A (CoA) conjugates is essential. Here we report the development of a rapid route to glycopeptide precursor CoA conjugates that affords both high yields and excellent purities. This synthesis route is applicable to the synthesis of peptide CoA-conjugates containing racemization-prone arylglycine residues: such residues are hallmarks of non-ribosomal peptide synthesis and have previously been inaccessible to peptide synthesis using Fmoc-type chemistry. We have applied this route to generate glycopeptide precursor peptides in their carrier protein-bound form as substrates to explore the specificity of the first oxygenase enzyme from vancomycin biosynthesis (OxyBvan). Our results indicate that OxyBvan is a highly promiscuous catalyst for phenolic coupling of diverse glycopeptide precursors that accepts multiple carrier protein substrates, even on carrier protein domains from alternate glycopeptide biosynthetic machineries. These results represent the first important steps in the development of an in vitro biomimetic synthesis of modified glycopeptide aglycones.