Complete set of detailed synthetic procedures and spectral data (PDF)

a-Ketoacid-hydroxylamine (KAHA) ligation allows the coupling of unprotected peptide segments through the chemoselective formation of an amide bond. Currently,t he most widely used variant employs a5 -membered cyclic hydroxylamine that forms ah omoserine ester as the primary ligation product. In order to directly form amide-linked threonine residues at the ligation site,w ep repared an ew 4membered cyclic hydroxylamine building block. This monomer was applied to the synthesis of wild-type ubiquitinconjugating enzyme UbcH5a (146 residues) and Titin protein domain TI I27 (89 residues). Both the resulting UbcH5a and the variant with two homoserine residues showed identical activity to ar ecombinant variant in aubiquitination assay.

A new method for the rapid preparation of chemically cross-linked hydrogels based on a multi-arm polyethylene glycol (PEG) bearing potassium acyl trifluoroborate (KAT) functional groups with multi-dentate amines is described.

We report the synthesis of monomers for atom‐transfer radical polymerization (ATRP) and a reversible addition‐fragmentation chain transfer (RAFT) agent bearing trifluoroborate iminiums (TIMs), which are quantitatively converted into potassium acyltrifluoroborates (KATs) after polymerization. The resulting KAT‐containing polymers are suitable for rapid amide‐forming ligations for both post‐polymerization modification and polymer conjugation. The polymer conjugation occurs rapidly, even under dilute (micromolar) aqueous conditions at ambient temperatures, thereby enabling the synthesis of a variety of linear and star‐shaped block copolymers. In addition, we applied post‐polymerization modification to the covalent linking of a photocaged cyclic antibiotic (gramicidin S) to the side chains of the KAT‐containing copolymer. Cellular assays revealed that the polymer–antibiotic conjugate is biocompatible and provides efficient light‐controlled release of the antibiotic on demand.

Synthetic folded insulin variants containing an ornithine‐hydroxylamine residue are readily modified in aqueous buffers by amide‐forming ligations with potassium acyltrifluoroborates (KATs). The synthetic insulin analogs were prepared by Fmoc‐SPPS, α‐ketoacid‐hydroxylamine (KAHA) ligation, and a prosthetic C‐peptide that delivers the correct disulfide pattern and allows facile incorporation at the B0 position of Glargine M2 of a new ornithine hydroxylamine protected with a photolabile group. The folded insulin is readily modified by photo‐deprotection followed by amide‐forming KAT ligation to give insulin variants labeled with dyes, lipids, and PEGs, as well as the formation of a covalent dimer.