Recent Advances in Primary Amine-Targeted Bioconjugation for Selective Protein Modification and Biomedical Applications

Primary amine-targeted bioconjugation connects proteins and other biomacromolecules with functional payloads for diagnosis and targeted therapy. However, conventional reagents such as N-hydroxysuccinimide esters often modify multiple surface lysines, producing heterogeneous conjugates with compromised activity and clinical performance. Recent advances therefore focus on site-selective, biocompatible reagents that enhance conjugation precision while preserving biomolecular function.This review systematically summarizes recent advances in primary amine-targeted bioconjugation, focusing on emerging reagents such as beta-alkoxy enones, azaphilones, sulfonyl acrylates, and dioxazolones. Through distinctive electronic effects and steric design, these reagents enable efficient and highly selective modification of primary amines under physiological conditions, while generating few by-products and exerting minimal effects on protein conformation. Although these new reagents have substantially addressed the poor specificity and limited biocompatibility of traditional primary amine bioconjugation reagents, achieving complete residue-specific protein modification in complex biological systems remains a major challenge. Future development is expected to move toward intelligent and modular platforms and to integrate multiple disciplines, thereby supporting innovation in antibody-drug conjugates (ADCs), diagnostic agents, and protein modification.