Asymmetric Catalysis at a Distance: Catalytic, Site-Selective Phosphorylation of Teicoplanin

摘要

We report three distinct, peptide-based catalysts that enable site-selective phosphorylation of three distinct hydroxyl groups within the complex glycopeptide antibiotic teicoplanin A_2-2. Two of the catalysts are based on a design that capitalizes on a catalyst-substrate interaction that mimics the biological mechanism of action for teicoplanin. These catalysts are based on a DXaa-DXaa peptide motif that is known to target the teicoplanin structure in a specific manner. The third was identified through evaluation of a set of catalysts that had been developed for historically distinct projects. Each catalyst contains additional functionality designed to dispose a catalytic moiety (a nucleophilic alkylimidazole) at a different region of the glycopeptide structure. A combination of mass spectrometry and 2D-NMR spectroscopy allowed structural assignment of the distinct phosphorylated teicoplanin derivatives. Mechanistic studies are also reported that support the hypotheses that led to the discovery ot the catalysts. In this manner, small molecule catalysts have been achieved that allow rational, catalytic control over reactions at sites that are separated by 11.6, 16.5, and nearly 17.7 A, based on the X-ray crystal structure of teicoplanin A_2-2. Finally, we report the biological activity of the new phosphorylated teicoplanin analoes and compare the results to the natural product itself.