# Philipp E. Schilling > Chemist developing amide-forming KAT ligation and organoboron protecting groups that make chemical protein synthesis possible at micromolar concentrations. Philipp E. Schilling is a synthetic chemist working on chemical protein synthesis, chemoselective ligation, and organoboron chemistry. He received his Ph.D. from ETH Zurich in the group of Jeffrey W. Bode. As first author with Samuel Steiner and Jeffrey W. Bode (Science, 2026), he introduced ONNO, a tetradentate ligand that masks potassium acyltrifluoroborates (KATs) as zwitterionic organoboron complexes during Fmoc solid-phase peptide synthesis. The resulting C-terminal peptide KATs were joined by KAT ligation at 100 to 200 micromolar concentrations, with about 50% conversion even at 20 micromolar, far below the millimolar concentrations that established protein ligation methods require. He also contributed to a copper-catalyzed route from carboxylic acids to KATs (Angewandte Chemie, 2022). He is now at the Department of Pathology, Stanford University. Canonical name: Philipp E. Schilling. Also published as: P. E. Schilling, Philipp Schilling, P. Schilling, PE Schilling. ORCID: https://orcid.org/0000-0003-4996-5367 ## Publications - [Zwitterionic organoboron complexes for overcoming the concentration barrier in chemical protein synthesis](https://schillingp.com/publications/zwitterionic-organoboron-complexes-protein-synthesis-science-2026/): Science 2026, doi:10.1126/science.aea7511. Chemical protein synthesis builds proteins by chemoselectively joining unprotected peptide segments, but the leading ligations (native chemical ligation and the alpha-ketoacid-hydroxylamine, or KAHA, ligation) need millimolar concentrations. That requirement fails for large, hydrophobic, or aggregation-prone segments that cannot be dissolved that concentrated. KAT ligation between potassium acyltrifluoroborates (KATs) and hydroxylamines is fast at low concentration, but had never been usable for protein synthesis because no protecting group could carry a KAT through Fmoc solid-phase peptide synthesis (SPPS). This work solves that problem with ONNO, a tetradentate ligand that masks a KAT as a bench-stable, SPPS- and acid-stable zwitterionic organoboron complex, then releases it under mild conditions. - [DMB labelling for detection and analysis of capsular polysaccharides](https://schillingp.com/publications/dmb-labelling-capsular-polysaccharides-biorxiv-2025/): bioRxiv 2025, doi:10.1101/2025.01.29.635457. Bacterial capsules are major virulence factors and vaccine antigens, but routine methods to detect and analyze them have largely disappeared. This preprint reports a biochemical method that releases ABC transporter-dependent (group 2 and 3) capsular polysaccharides by mild acid hydrolysis of their Kdo linkages and fluorescently tags them with DMB (1,2-diamino-4,5-methylenedioxybenzene). Anion-exchange chromatography of the labelled material reveals the presence, relative abundance, and length distribution of these antigens in extraintestinal pathogenic Escherichia coli (ExPEC). Philipp E. Schilling contributed insights into the DMB labelling chemistry. - [Potassium Acyltrifluoroborates (KATs) for Chemical Protein Synthesis and Modifications](https://schillingp.com/publications/kats-for-chemical-protein-synthesis-phd-thesis-eth-2025/): ETH Zurich 2025, doi:. Doctoral thesis (ETH Zurich, group of Jeffrey W. Bode) on the use of potassium acyltrifluoroborates for chemical protein synthesis and protein modification, including the development of organoboron protecting-group strategies that enable KAT ligation of peptide segments at low concentration. - [Heterobifunctional Linker](https://schillingp.com/publications/heterobifunctional-linker-patent-2025/): European Patent Application 2025, doi:. European patent application describing a heterobifunctional linker for bioconjugation. Inventors include Philipp E. Schilling. - [Preparation of Potassium Acyltrifluoroborates (KATs) from Carboxylic Acids by Copper-Catalyzed Borylation of Mixed Anhydrides](https://schillingp.com/publications/potassium-acyltrifluoroborates-from-carboxylic-acids-angewandte-2021/): Angew. Chem. Int. Ed. 2021, doi:10.1002/anie.202114513. Potassium acyltrifluoroborates (KATs) are the acylboron partners in KAT ligation, but before this work the only route from a carboxylic acid used a hard-to-handle borylzinc reagent. Here carboxylic acids are activated as isobutyl mixed anhydrides with isobutyl chloroformate and N-methylmorpholine, then borylated with bis(pinacolato)diboron under a commercial N-heterocyclic-carbene copper catalyst (IMesCuCl) with sodium methoxide as base, and finally converted to the KAT with aqueous potassium bifluoride (KHF2). - [Mannosylated hemagglutinin peptides bind cyanovirin-N independent of disulfide-bonds in complementary binding sites](https://schillingp.com/publications/mannosylated-hemagglutinin-peptides-cyanovirin-n-rsc-advances-2020/): RSC Adv. 2020, doi:10.1039/d0ra01128b. Cyanovirin-N (CV-N) is an antiviral lectin that binds high-mannose glycans on enveloped viruses. This study synthesized influenza hemagglutinin-derived peptides carrying mannose units attached through triazole linkers and measured their binding to CV-N variants with reduced disulfide content, including a variant in which one disulfide was replaced by an engineered glutamate/arginine ion pair. - [Studies of the binding of glycosylated peptides and influenza glycoproteins to recombinantly expressed Cyanovirin-N](https://schillingp.com/publications/glycosylated-peptides-cyanovirin-n-msc-thesis-vienna-2018/): University of Vienna 2018, doi:. Master's thesis (University of Vienna) on the synthesis of glycosylated peptides and the binding of influenza glycoproteins to recombinantly expressed cyanovirin-N. This work is the basis of the 2020 RSC Advances paper on mannosylated hemagglutinin peptides and cyanovirin-N. ## Topics - [KAT ligation](https://schillingp.com/research/kat-ligation/): An overview of KAT ligation, the chemoselective amide-forming reaction between potassium acyltrifluoroborates and hydroxylamines, and its use in chemical protein synthesis and bioconjugation. ## Optional - [All references as BibTeX](https://schillingp.com/publications.bib) - [Google Scholar profile](https://scholar.google.com/citations?user=jJv11PUAAAAJ)