Process Optimization for the Synthesis of Enzyme-Cleavable Val-Cit Dipeptide Linker in Antibody–Drug Conjugate Production

An optimized synthesis of the enzyme-cleavable Val-Cit dipeptide linker, a critical component in antibody–drug conjugates (ADCs) is reported. By substituting HATU for EEDQ as condensing agent, the revised synthetic route effectively suppresses side oxazolone formation and eliminates racemization, thereby significantly enhancing the yield. Additionally, the influence of various deprotecting agents was systematically evaluated, revealing that diethylamine and piperidine exhibit superior efficiency. MC-Val-Cit-PAB-MMAE was successfully synthesized in eight steps with an overall yield of 14%, which represents an 8% improvement in the key step compared to previously reported values. This study thus offers a more efficient and reliable method for ADC linker synthesis.