Hydrazide-Based Toolkit for Chemical Synthesis of Peptides and Proteins

Chemical protein synthesis offers a powerful platform for elucidating protein function and constructing engineered proteins with tailored properties. Despite its broad utility, several challenges remain in the synthesis and handling of peptides and proteins. In this account, we describe the development of a series of synthetic strategies that exploit the distinctive reactivity and versatility of peptide hydrazides. First, we established a method for the direct thioesterification of N-terminal thiazolidine-containing peptide hydrazides, effectively suppressing undesired thiazolidine ring-opening side reactions. Second, we introduced a late-stage solubilization technique based on reductive N-alkylation of hydrazides with hydrophilic tags, enabling improved purification and ligation of poorly soluble peptides. Third, we developed a solid-phase linker that generates alkyl hydrazides, dramatically enhancing HPLC peak resolution and purification yields. Finally, we synthesized aspartic acid hydrazides that suppress aspartimide formation during solid-phase synthesis, including under microwave-assisted conditions. Collectively, these hydrazide-based methodologies constitute a unified and practical toolkit for overcoming persistent bottlenecks in chemical peptide and protein synthesis.