Improved synthesis of (S)-N-Boc-5-oxaproline for protein synthesis with the α-ketoacid-hydroxylamine (KAHA) ligation

Advanced Pyrrolidine-Carbamate Self-Immolative Spacer with Tertiary Amine Handle Induces Superfast Cyclative Drug Release

Amine-carbamate self-immolative (SI) spacers represent practical and versatile tools in targeted prodrugs, but their slow degradation mechanism limits drug activation at the site of disease. We engineered a pyrrolidine-carbamate SI spacer with a tertiary amine handle which strongly accelerates the spacer cyclization to give a bicyclic urea and the free hydroxy groups of either cytotoxic (Camptothecin) or immunostimulatory (Resiquimod) drugs. In silico conformational analysis and p K a calculations suggest a plausible mechanism for the superior efficacy of the advanced SI spacer compared to state-of-art analogues.

Chemical Protein Synthesis by Chemoselective #x03B1;-Ketoacid-Hydroxylamine (KAHA) Ligations with 5-Oxaproline

Chemical protein synthesis enables the precise construction of proteins by employing solid-phase peptide synthesis and chemoselective ligations. One such chemoselective reaction suitable for protein synthesis is the α-Ketoacid-Hydroxylamine (KAHA) ligation. Fully unprotected peptides are ligated by a selective reaction between α-ketoacids and hydroxylamines to give native amide bonds. Herein, we describe the chemical synthesis of ubiquitin by a two-segment approach using the 5-oxaproline hydroxylamine.

Ligation Technologies for the Synthesis of Cyclic Peptides

Cyclic peptides have been attracting a lot of attention in recent decades, especially in the area of drug discovery, as more and more naturally occurring cyclic peptides with diverse biological activities have been discovered. Chemical synthesis of cyclic peptides is essential when studying their structure-activity relationships. Conventional peptide cyclization methods via direct coupling have inherent limitations, like the susceptibility to epimerization at the C-terminus, poor solubility of fully protected peptide precursors, and low yield caused by oligomerization. In this regard, chemoselective ligation-mediated cyclization methods have emerged as effective strategies for cyclic peptide synthesis. The toolbox for cyclic peptide synthesis has been expanded substantially in the past two decades, allowing more efficient synthesis of cyclic peptides with various scaffolds and modifications. This Review will explore different chemoselective ligation technologies used for cyclic peptide synthesis that generate both native and unnatural peptide linkages. The practical issues and limitations of different methods will be discussed. The advance in cyclic peptide synthesis will benefit the biological and medicinal study of cyclic peptides, an important class of macrocycles with potentials in numerous fields, notably in therapeutics.

Catalytic asymmetric aza-Michael addition of fumaric monoacids with multifunctional thiourea/boronic acids

Chiral multifunctional thiourea/boronic acid catalysts enabled the synthesis of N-hydroxyaspartate derivatives applicable for KAHA amidation through acid-β selective aza-Michael addition.

One-pot multi-segment condensation strategies for chemical protein synthesis

This paper describes recent advances of one-pot multi-segment condensation strategies based on kinetically controlled strategies and/or protecting group-removal strategies in chemical protein synthesis.